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70 changed files (+17365/-4831)
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@@ -1,3 +1,3 @@WARNING: Please do not open a pull request in this repository. This is not the relevant repository to contribute to Mathematics in Lean. This repository is cloned by people who want to study the book. It is automatically created from the source repository which can be found at https://github.com/avigad/mathematics_in_lean_source and where you can open a pull-request. This is not the relevant repository to contribute to Mathematics in Lean. This repository is cloned by people who want to study the book. It is automatically created from the source repository which can be found at https://github.com/avigad/mathematics_in_lean_source and where you can open a pull-request.
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@@ -104,7 +104,7 @@ example (h : ¬FnHasUb f) : ∀ a, ∃ x, f x > a := byexample (h : ¬Monotone f) : ∃ x y, x ≤ y ∧ f y < f x := by rw [Monotone] at h push_neg at h push_neg at h exact h end
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@@ -57,7 +57,7 @@ theorem sb_injective (hf : Injective f) : Injective (sbFun f g) := bysimp [sbAux] exact ⟨x₁, hn, x₂eq.symm⟩ sorry push_neg at xA push_neg at xA sorry theorem sb_surjective (hg : Injective g) : Surjective (sbFun f g) := by
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@@ -59,7 +59,7 @@ theorem sb_injective (hf : Injective f) : Injective (sbFun f g) := byexact ⟨x₁, hn, x₂eq.symm⟩ rw [if_pos x₁A, if_pos x₂A] at hxeq exact hf hxeq push_neg at xA push_neg at xA rw [if_neg xA.1, if_neg xA.2] at hxeq rw [← sb_right_inv f g xA.1, hxeq, sb_right_inv f g xA.2]
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@@ -50,7 +50,7 @@ theorem primes_infinite : ∀ n, ∃ p > n, Nat.Prime p := byrefine ⟨p, ?_, pp⟩ show p > n by_contra ple push_neg at ple push_neg at ple have : p ∣ Nat.factorial (n + 1) := by sorry have : p ∣ 1 := by
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@@ -39,7 +39,7 @@ theorem primes_infinite : ∀ n, ∃ p > n, Nat.Prime p := byrefine ⟨p, ?_, pp⟩ show p > n by_contra ple push_neg at ple push_neg at ple have : p ∣ Nat.factorial (n + 1) := by apply Nat.dvd_factorial apply pp.pos
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@@ -171,7 +171,6 @@ theorem abs_mod'_le (a b : ℤ) (h : 0 < b) : |mod' a b| ≤ b / 2 := byhave := Int.emod_lt_of_pos (a + b / 2) h have := Int.ediv_add_emod b 2 have := Int.emod_lt_of_pos b zero_lt_two revert this; intro this -- FIXME, this should not be needed linarith theorem mod'_eq (a b : ℤ) : mod' a b = a - b * div' a b := by linarith [div'_add_mod' a b]
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@@ -247,7 +246,7 @@ theorem natAbs_norm_mod_lt (x y : GaussInt) (hy : y ≠ 0) :(x % y).norm.natAbs < y.norm.natAbs := by apply Int.ofNat_lt.1 simp only [Int.natCast_natAbs, abs_of_nonneg, norm_nonneg] apply norm_mod_lt x hy exact norm_mod_lt x hy theorem not_norm_mul_left_lt_norm (x : GaussInt) {y : GaussInt} (hy : y ≠ 0) : ¬(norm (x * y)).natAbs < (norm x).natAbs := by
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@@ -162,7 +162,6 @@ theorem abs_mod'_le (a b : ℤ) (h : 0 < b) : |mod' a b| ≤ b / 2 := byhave := Int.emod_lt_of_pos (a + b / 2) h have := Int.ediv_add_emod b 2 have := Int.emod_lt_of_pos b zero_lt_two revert this; intro this -- FIXME, this should not be needed linarith theorem mod'_eq (a b : ℤ) : mod' a b = a - b * div' a b := by linarith [div'_add_mod' a b]
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@@ -261,7 +260,7 @@ theorem natAbs_norm_mod_lt (x y : GaussInt) (hy : y ≠ 0) :(x % y).norm.natAbs < y.norm.natAbs := by apply Int.ofNat_lt.1 simp only [Int.natCast_natAbs, abs_of_nonneg, norm_nonneg] apply norm_mod_lt x hy exact norm_mod_lt x hy theorem not_norm_mul_left_lt_norm (x : GaussInt) {y : GaussInt} (hy : y ≠ 0) : ¬(norm (x * y)).natAbs < (norm x).natAbs := by
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@@ -3,8 +3,6 @@ import Mathlib.MeasureTheory.Integral.IntervalIntegralimport Mathlib.Analysis.SpecialFunctions.Integrals import Mathlib.Analysis.Convolution local macro_rules | `($x ^ $y) => `(HPow.hPow $x $y) open Set Filter open Topology Filter
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@@ -3,8 +3,6 @@ import Mathlib.MeasureTheory.Integral.IntervalIntegralimport Mathlib.Analysis.SpecialFunctions.Integrals import Mathlib.Analysis.Convolution local macro_rules | `($x ^ $y) => `(HPow.hPow $x $y) open Set Filter open Topology Filter
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@@ -36,7 +36,7 @@ Do the following:You can call the copy `my_files` or whatever you want and use it to create your own Lean files as well. At that point, you can open the textbook in a web browser At that point, you can open the textbook in a web browser at [https://leanprover-community.github.io/mathematics_in_lean/](https://leanprover-community.github.io/mathematics_in_lean/) and start reading and doing the exercises in VS Code.
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@@ -1,4 +1,4 @@# Sphinx build info version 1 # This file records the configuration used when building these files. When it is not found, a full rebuild will be done. config: 5f7d574404b36ea843014084d74003d7 # This file hashes the configuration used when building these files. When it is not found, a full rebuild will be done. config: 9821478498fa33697c987b601aae688f tags: 645f666f9bcd5a90fca523b33c5a78b7
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@@ -1,23 +1,23 @@<!DOCTYPE html> <html class="writer-html5" lang="en" data-content_root="./"> <html class="writer-html5" lang="en" > <head> <meta charset="utf-8" /><meta name="viewport" content="width=device-width, initial-scale=1" /> <meta charset="utf-8" /><meta name="generator" content="Docutils 0.17.1: http://docutils.sourceforge.net/" /> <meta name="viewport" content="width=device-width, initial-scale=1.0" /> <title>1. Introduction — Mathematics in Lean 0.1 documentation</title> <link rel="stylesheet" type="text/css" href="_static/pygments.css?v=80d5e7a1" /> <link rel="stylesheet" type="text/css" href="_static/css/theme.css?v=e59714d7" /> <link rel="stylesheet" type="text/css" href="_static/css/custom.css?v=0731ccc3" /> <link rel="stylesheet" href="_static/pygments.css" type="text/css" /> <link rel="stylesheet" href="_static/css/theme.css" type="text/css" /> <link rel="stylesheet" href="_static/css/custom.css" type="text/css" /> <link rel="shortcut icon" href="_static/favicon.ico"/> <script src="_static/jquery.js?v=5d32c60e"></script> <script src="_static/_sphinx_javascript_frameworks_compat.js?v=2cd50e6c"></script> <script src="_static/documentation_options.js?v=2709fde1"></script> <script src="_static/doctools.js?v=9bcbadda"></script> <script src="_static/sphinx_highlight.js?v=dc90522c"></script> <!--[if lt IE 9]> <script src="_static/js/html5shiv.min.js"></script> <![endif]--> <script data-url_root="./" id="documentation_options" src="_static/documentation_options.js"></script> <script src="_static/jquery.js"></script> <script src="_static/underscore.js"></script> <script src="_static/_sphinx_javascript_frameworks_compat.js"></script> <script src="_static/doctools.js"></script> <script src="_static/js/theme.js"></script> <link rel="index" title="Index" href="genindex.html" /> <link rel="search" title="Search" href="search.html" />
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@@ -30,15 +30,11 @@<nav data-toggle="wy-nav-shift" class="wy-nav-side"> <div class="wy-side-scroll"> <div class="wy-side-nav-search" > <a href="index.html" class="icon icon-home"> Mathematics in Lean <a href="index.html" class="icon icon-home"> Mathematics in Lean </a> <div role="search"> <form id="rtd-search-form" class="wy-form" action="search.html" method="get"> <input type="text" name="q" placeholder="Search docs" aria-label="Search docs" /> <input type="text" name="q" placeholder="Search docs" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form>
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@@ -79,8 +75,8 @@<div class="rst-content"> <div role="navigation" aria-label="Page navigation"> <ul class="wy-breadcrumbs"> <li><a href="index.html" class="icon icon-home" aria-label="Home"></a></li> <li class="breadcrumb-item active"><span class="section-number">1. </span>Introduction</li> <li><a href="index.html" class="icon icon-home"></a> »</li> <li><span class="section-number">1. </span>Introduction</li> <li class="wy-breadcrumbs-aside"> <a href="_sources/C01_Introduction.rst.txt" rel="nofollow"> View page source</a> </li>
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@@ -91,9 +87,9 @@<div itemprop="articleBody"> <section id="introduction"> <span id="id1"></span><h1><span class="section-number">1. </span>Introduction<a class="headerlink" href="#introduction" title="Link to this heading"></a></h1> <span id="id1"></span><h1><span class="section-number">1. </span>Introduction<a class="headerlink" href="#introduction" title="Permalink to this heading"></a></h1> <section id="getting-started"> <h2><span class="section-number">1.1. </span>Getting Started<a class="headerlink" href="#getting-started" title="Link to this heading"></a></h2> <h2><span class="section-number">1.1. </span>Getting Started<a class="headerlink" href="#getting-started" title="Permalink to this heading"></a></h2> <p>The goal of this book is to teach you to formalize mathematics using the Lean 4 interactive proof assistant. It assumes that you know some mathematics, but it does not require much.
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@@ -160,7 +156,7 @@ which is why we suggested making a copy.)</p><p>We intend for you to work on the exercises in the <code class="docutils literal notranslate"><span class="pre">MIL</span></code> folder while reading the textbook, which contains explanations, instructions, and hints. The text will often include examples, like this one:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#eval</span><span class="w"> </span><span class="s2">"Hello, World!"</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#eval</span> <span class="s2">"Hello, World!"</span> </pre></div> </div> <p>You should be able to find the corresponding example in the associated
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@@ -180,42 +176,42 @@ You can always compare your solutions to the ones in the <code class="docutils lfolder associated with each section.</p> </section> <section id="overview"> <h2><span class="section-number">1.2. </span>Overview<a class="headerlink" href="#overview" title="Link to this heading"></a></h2> <h2><span class="section-number">1.2. </span>Overview<a class="headerlink" href="#overview" title="Permalink to this heading"></a></h2> <p>Put simply, Lean is a tool for building complex expressions in a formal language known as <em>dependent type theory</em>.</p> <p id="index-0">Every expression has a <em>type</em>, and you can use the <cite>#check</cite> command to print it. Some expressions have types like <cite>ℕ</cite> or <cite>ℕ → ℕ</cite>. These are mathematical objects.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">2</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="mi">2</span> <span class="bp">+</span> <span class="mi">2</span> <span class="kd">def</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">3</span> <span class="kd">def</span> <span class="n">f</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">:=</span> <span class="n">x</span> <span class="bp">+</span> <span class="mi">3</span> <span class="k">#check</span><span class="w"> </span><span class="n">f</span> <span class="k">#check</span> <span class="n">f</span> </pre></div> </div> <p>Some expressions have type <cite>Prop</cite>. These are mathematical statements.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">4</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="mi">2</span> <span class="bp">+</span> <span class="mi">2</span> <span class="bp">=</span> <span class="mi">4</span> <span class="kd">def</span><span class="w"> </span><span class="n">FermatLastTheorem</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">,</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="n">n</span> <span class="kd">def</span> <span class="n">FermatLastTheorem</span> <span class="o">:=</span> <span class="bp">∀</span> <span class="n">x</span> <span class="n">y</span> <span class="n">z</span> <span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">,</span> <span class="n">n</span> <span class="bp">></span> <span class="mi">2</span> <span class="bp">∧</span> <span class="n">x</span> <span class="bp">*</span> <span class="n">y</span> <span class="bp">*</span> <span class="n">z</span> <span class="bp">≠</span> <span class="mi">0</span> <span class="bp">→</span> <span class="n">x</span> <span class="bp">^</span> <span class="n">n</span> <span class="bp">+</span> <span class="n">y</span> <span class="bp">^</span> <span class="n">n</span> <span class="bp">≠</span> <span class="n">z</span> <span class="bp">^</span> <span class="n">n</span> <span class="k">#check</span><span class="w"> </span><span class="n">FermatLastTheorem</span> <span class="k">#check</span> <span class="n">FermatLastTheorem</span> </pre></div> </div> <p>Some expressions have a type, <cite>P</cite>, where <cite>P</cite> itself has type <cite>Prop</cite>. Such an expression is a proof of the proposition <cite>P</cite>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">easy</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">easy</span> <span class="o">:</span> <span class="mi">2</span> <span class="bp">+</span> <span class="mi">2</span> <span class="bp">=</span> <span class="mi">4</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="k">#check</span><span class="w"> </span><span class="n">easy</span> <span class="k">#check</span> <span class="n">easy</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">hard</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FermatLastTheorem</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">theorem</span> <span class="n">hard</span> <span class="o">:</span> <span class="n">FermatLastTheorem</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="k">#check</span><span class="w"> </span><span class="n">hard</span> <span class="k">#check</span> <span class="n">hard</span> </pre></div> </div> <p>If you manage to construct an expression of type <code class="docutils literal notranslate"><span class="pre">FermatLastTheorem</span></code> and
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@@ -244,27 +240,27 @@ we can write down the expressions themselvesor we can provide Lean with <em>instructions</em> as to how to construct them. For example, the following expression represents a proof of the fact that if <code class="docutils literal notranslate"><span class="pre">n</span></code> is even then so is <code class="docutils literal notranslate"><span class="pre">m</span> <span class="pre">*</span> <span class="pre">n</span></code>:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat</span><span class="o">,</span><span class="w"> </span><span class="n">Even</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Even</span><span class="w"> </span><span class="o">(</span><span class="n">m</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">⟨</span><span class="n">k</span><span class="o">,</span><span class="w"> </span><span class="o">(</span><span class="n">hk</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">k</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">k</span><span class="o">)⟩</span><span class="w"> </span><span class="bp">↦</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">hmn</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">k</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">k</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">hk</span><span class="o">,</span><span class="w"> </span><span class="n">mul_add</span><span class="o">]</span> <span class="w"> </span><span class="k">show</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">l</span><span class="o">,</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">l</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">l</span><span class="w"> </span><span class="k">from</span><span class="w"> </span><span class="o">⟨</span><span class="n">_</span><span class="o">,</span><span class="w"> </span><span class="n">hmn</span><span class="o">⟩</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">m</span> <span class="n">n</span> <span class="o">:</span> <span class="n">Nat</span><span class="o">,</span> <span class="n">Even</span> <span class="n">n</span> <span class="bp">→</span> <span class="n">Even</span> <span class="o">(</span><span class="n">m</span> <span class="bp">*</span> <span class="n">n</span><span class="o">)</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">m</span> <span class="n">n</span> <span class="o">⟨</span><span class="n">k</span><span class="o">,</span> <span class="o">(</span><span class="n">hk</span> <span class="o">:</span> <span class="n">n</span> <span class="bp">=</span> <span class="n">k</span> <span class="bp">+</span> <span class="n">k</span><span class="o">)⟩</span> <span class="bp">↦</span> <span class="k">have</span> <span class="n">hmn</span> <span class="o">:</span> <span class="n">m</span> <span class="bp">*</span> <span class="n">n</span> <span class="bp">=</span> <span class="n">m</span> <span class="bp">*</span> <span class="n">k</span> <span class="bp">+</span> <span class="n">m</span> <span class="bp">*</span> <span class="n">k</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">hk</span><span class="o">,</span> <span class="n">mul_add</span><span class="o">]</span> <span class="k">show</span> <span class="bp">∃</span> <span class="n">l</span><span class="o">,</span> <span class="n">m</span> <span class="bp">*</span> <span class="n">n</span> <span class="bp">=</span> <span class="n">l</span> <span class="bp">+</span> <span class="n">l</span> <span class="k">from</span> <span class="o">⟨</span><span class="n">_</span><span class="o">,</span> <span class="n">hmn</span><span class="o">⟩</span> </pre></div> </div> <p>The <em>proof term</em> can be compressed to a single line:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat</span><span class="o">,</span><span class="w"> </span><span class="n">Even</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Even</span><span class="w"> </span><span class="o">(</span><span class="n">m</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="k">fun</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">⟨</span><span class="n">k</span><span class="o">,</span><span class="w"> </span><span class="n">hk</span><span class="o">⟩</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="o">⟨</span><span class="n">m</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">k</span><span class="o">,</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">hk</span><span class="o">,</span><span class="w"> </span><span class="n">mul_add</span><span class="o">]⟩</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">m</span> <span class="n">n</span> <span class="o">:</span> <span class="n">Nat</span><span class="o">,</span> <span class="n">Even</span> <span class="n">n</span> <span class="bp">→</span> <span class="n">Even</span> <span class="o">(</span><span class="n">m</span> <span class="bp">*</span> <span class="n">n</span><span class="o">)</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">m</span> <span class="n">n</span> <span class="o">⟨</span><span class="n">k</span><span class="o">,</span> <span class="n">hk</span><span class="o">⟩</span> <span class="bp">↦</span> <span class="o">⟨</span><span class="n">m</span> <span class="bp">*</span> <span class="n">k</span><span class="o">,</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">hk</span><span class="o">,</span> <span class="n">mul_add</span><span class="o">]⟩</span> </pre></div> </div> <p>The following is, instead, a <em>tactic-style</em> proof of the same theorem, where lines starting with <code class="docutils literal notranslate"><span class="pre">--</span></code> are comments, hence ignored by Lean:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat</span><span class="o">,</span><span class="w"> </span><span class="n">Even</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Even</span><span class="w"> </span><span class="o">(</span><span class="n">m</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="c1">-- Say `m` and `n` are natural numbers, and assume `n = 2 * k`.</span> <span class="w"> </span><span class="n">rintro</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">⟨</span><span class="n">k</span><span class="o">,</span><span class="w"> </span><span class="n">hk</span><span class="o">⟩</span> <span class="w"> </span><span class="c1">-- We need to prove `m * n` is twice a natural number. Let's show it's twice `m * k`.</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">k</span> <span class="w"> </span><span class="c1">-- Substitute for `n`,</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">hk</span><span class="o">]</span> <span class="w"> </span><span class="c1">-- and now it's obvious.</span> <span class="w"> </span><span class="n">ring</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">m</span> <span class="n">n</span> <span class="o">:</span> <span class="n">Nat</span><span class="o">,</span> <span class="n">Even</span> <span class="n">n</span> <span class="bp">→</span> <span class="n">Even</span> <span class="o">(</span><span class="n">m</span> <span class="bp">*</span> <span class="n">n</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="c1">-- Say `m` and `n` are natural numbers, and assume `n = 2 * k`.</span> <span class="n">rintro</span> <span class="n">m</span> <span class="n">n</span> <span class="o">⟨</span><span class="n">k</span><span class="o">,</span> <span class="n">hk</span><span class="o">⟩</span> <span class="c1">-- We need to prove `m * n` is twice a natural number. Let's show it's twice `m * k`.</span> <span class="n">use</span> <span class="n">m</span> <span class="bp">*</span> <span class="n">k</span> <span class="c1">-- Substitute for `n`,</span> <span class="n">rw</span> <span class="o">[</span><span class="n">hk</span><span class="o">]</span> <span class="c1">-- and now it's obvious.</span> <span class="n">ring</span> </pre></div> </div> <p>As you enter each line of such a proof in VS Code,
-
@@ -296,8 +292,8 @@ We will also see that, conversely,it is often useful to insert a short proof term in the middle of a tactic proof. That said, in this book, our emphasis will be on the use of tactics.</p> <p>In our example, the tactic proof can also be reduced to a one-liner:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat</span><span class="o">,</span><span class="w"> </span><span class="n">Even</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Even</span><span class="w"> </span><span class="o">(</span><span class="n">m</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rintro</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">⟨</span><span class="n">k</span><span class="o">,</span><span class="w"> </span><span class="n">hk</span><span class="o">⟩</span><span class="bp">;</span><span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">k</span><span class="bp">;</span><span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">hk</span><span class="o">]</span><span class="bp">;</span><span class="w"> </span><span class="n">ring</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">m</span> <span class="n">n</span> <span class="o">:</span> <span class="n">Nat</span><span class="o">,</span> <span class="n">Even</span> <span class="n">n</span> <span class="bp">→</span> <span class="n">Even</span> <span class="o">(</span><span class="n">m</span> <span class="bp">*</span> <span class="n">n</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rintro</span> <span class="n">m</span> <span class="n">n</span> <span class="o">⟨</span><span class="n">k</span><span class="o">,</span> <span class="n">hk</span><span class="o">⟩</span><span class="bp">;</span> <span class="n">use</span> <span class="n">m</span> <span class="bp">*</span> <span class="n">k</span><span class="bp">;</span> <span class="n">rw</span> <span class="o">[</span><span class="n">hk</span><span class="o">]</span><span class="bp">;</span> <span class="n">ring</span> </pre></div> </div> <p>Here we have used tactics to carry out small proof steps.
-
@@ -306,8 +302,8 @@ and justify longer calculations and bigger inferential steps.For example, we can invoke Lean’s simplifier with specific rules for simplifying statements about parity to prove our theorem automatically.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat</span><span class="o">,</span><span class="w"> </span><span class="n">Even</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Even</span><span class="w"> </span><span class="o">(</span><span class="n">m</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intros</span><span class="bp">;</span><span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="o">[</span><span class="bp">*</span><span class="o">,</span><span class="w"> </span><span class="n">parity_simps</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">m</span> <span class="n">n</span> <span class="o">:</span> <span class="n">Nat</span><span class="o">,</span> <span class="n">Even</span> <span class="n">n</span> <span class="bp">→</span> <span class="n">Even</span> <span class="o">(</span><span class="n">m</span> <span class="bp">*</span> <span class="n">n</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intros</span><span class="bp">;</span> <span class="n">simp</span> <span class="o">[</span><span class="bp">*</span><span class="o">,</span> <span class="n">parity_simps</span><span class="o">]</span> </pre></div> </div> <p>Another big difference between the two introductions is that
-
@@ -354,9 +350,9 @@ Marc Huisinga,Benjamin Jones, Julian Külshammer, Victor Liu, Jimmy Lu, Martin C. Martin, Giovanni Mascellani, John McDowell, Isaiah Mindich, Hunter Monroe, Pietro Monticone, Oliver Nash, Emanuelle Natale, Martin C. Martin, Giovanni Mascellani, John McDowell, Bhavik Mehta, Isaiah Mindich, Kabelo Moiloa, Hunter Monroe, Pietro Monticone, Oliver Nash, Emanuelle Natale, Filippo A. E. Nuccio, Pim Otte, Bartosz Piotrowski, Nicolas Rolland, Keith Rush,
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-
-
@@ -1,24 +1,24 @@<!DOCTYPE html> <html class="writer-html5" lang="en" data-content_root="./"> <html class="writer-html5" lang="en" > <head> <meta charset="utf-8" /><meta name="viewport" content="width=device-width, initial-scale=1" /> <meta charset="utf-8" /><meta name="generator" content="Docutils 0.17.1: http://docutils.sourceforge.net/" /> <meta name="viewport" content="width=device-width, initial-scale=1.0" /> <title>2. Basics — Mathematics in Lean 0.1 documentation</title> <link rel="stylesheet" type="text/css" href="_static/pygments.css?v=80d5e7a1" /> <link rel="stylesheet" type="text/css" href="_static/css/theme.css?v=e59714d7" /> <link rel="stylesheet" type="text/css" href="_static/css/custom.css?v=0731ccc3" /> <link rel="stylesheet" href="_static/pygments.css" type="text/css" /> <link rel="stylesheet" href="_static/css/theme.css" type="text/css" /> <link rel="stylesheet" href="_static/css/custom.css" type="text/css" /> <link rel="shortcut icon" href="_static/favicon.ico"/> <script src="_static/jquery.js?v=5d32c60e"></script> <script src="_static/_sphinx_javascript_frameworks_compat.js?v=2cd50e6c"></script> <script src="_static/documentation_options.js?v=2709fde1"></script> <script src="_static/doctools.js?v=9bcbadda"></script> <script src="_static/sphinx_highlight.js?v=dc90522c"></script> <script async="async" src="https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js"></script> <!--[if lt IE 9]> <script src="_static/js/html5shiv.min.js"></script> <![endif]--> <script data-url_root="./" id="documentation_options" src="_static/documentation_options.js"></script> <script src="_static/jquery.js"></script> <script src="_static/underscore.js"></script> <script src="_static/_sphinx_javascript_frameworks_compat.js"></script> <script src="_static/doctools.js"></script> <script async="async" src="https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js"></script> <script src="_static/js/theme.js"></script> <link rel="index" title="Index" href="genindex.html" /> <link rel="search" title="Search" href="search.html" />
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@@ -31,15 +31,11 @@<nav data-toggle="wy-nav-shift" class="wy-nav-side"> <div class="wy-side-scroll"> <div class="wy-side-nav-search" > <a href="index.html" class="icon icon-home"> Mathematics in Lean <a href="index.html" class="icon icon-home"> Mathematics in Lean </a> <div role="search"> <form id="rtd-search-form" class="wy-form" action="search.html" method="get"> <input type="text" name="q" placeholder="Search docs" aria-label="Search docs" /> <input type="text" name="q" placeholder="Search docs" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form>
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@@ -83,8 +79,8 @@<div class="rst-content"> <div role="navigation" aria-label="Page navigation"> <ul class="wy-breadcrumbs"> <li><a href="index.html" class="icon icon-home" aria-label="Home"></a></li> <li class="breadcrumb-item active"><span class="section-number">2. </span>Basics</li> <li><a href="index.html" class="icon icon-home"></a> »</li> <li><span class="section-number">2. </span>Basics</li> <li class="wy-breadcrumbs-aside"> <a href="_sources/C02_Basics.rst.txt" rel="nofollow"> View page source</a> </li>
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@@ -95,13 +91,13 @@<div itemprop="articleBody"> <section id="basics"> <span id="id1"></span><h1><span class="section-number">2. </span>Basics<a class="headerlink" href="#basics" title="Link to this heading"></a></h1> <span id="id1"></span><h1><span class="section-number">2. </span>Basics<a class="headerlink" href="#basics" title="Permalink to this heading"></a></h1> <p>This chapter is designed to introduce you to the nuts and bolts of mathematical reasoning in Lean: calculating, applying lemmas and theorems, and reasoning about generic structures.</p> <section id="calculating"> <h2><span class="section-number">2.1. </span>Calculating<a class="headerlink" href="#calculating" title="Link to this heading"></a></h2> <h2><span class="section-number">2.1. </span>Calculating<a class="headerlink" href="#calculating" title="Permalink to this heading"></a></h2> <p>We generally learn to carry out mathematical calculations without thinking of them as proofs. But when we justify each step in a calculation,
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@@ -123,9 +119,9 @@ so the left-hand side of <code class="docutils literal notranslate"><span class=However, it is generally good style to be mindful of Lean’s notational conventions and leave out parentheses when Lean does as well.</p> <p>Let’s try out <code class="docutils literal notranslate"><span class="pre">rw</span></code>.</p> <div class="highlight-lean notranslate" id="index-1"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">mul_comm</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="o">]</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">mul_assoc</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">c</span><span class="o">]</span> <div class="highlight-lean notranslate" id="index-1"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">c</span> <span class="bp">=</span> <span class="n">b</span> <span class="bp">*</span> <span class="o">(</span><span class="n">a</span> <span class="bp">*</span> <span class="n">c</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">mul_comm</span> <span class="n">a</span> <span class="n">b</span><span class="o">]</span> <span class="n">rw</span> <span class="o">[</span><span class="n">mul_assoc</span> <span class="n">b</span> <span class="n">a</span> <span class="n">c</span><span class="o">]</span> </pre></div> </div> <p>The <code class="docutils literal notranslate"><span class="pre">import</span></code> lines at the beginning of the associated examples file
-
@@ -149,12 +145,12 @@ Lean reports on the current <em>proof state</em> in theAs you move your cursor past each step of the proof, you can see the state change. A typical proof state in Lean might look as follows:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="mi">1</span><span class="w"> </span><span class="n">goal</span> <span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">,</span> <span class="n">h₁</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Prime</span><span class="w"> </span><span class="n">x</span><span class="o">,</span> <span class="n">h₂</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬</span><span class="n">Even</span><span class="w"> </span><span class="n">x</span><span class="o">,</span> <span class="n">h₃</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="n">x</span> <span class="bp">⊢</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">≥</span><span class="w"> </span><span class="mi">4</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="mi">1</span> <span class="n">goal</span> <span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">,</span> <span class="n">h₁</span> <span class="o">:</span> <span class="n">Prime</span> <span class="n">x</span><span class="o">,</span> <span class="n">h₂</span> <span class="o">:</span> <span class="bp">¬</span><span class="n">Even</span> <span class="n">x</span><span class="o">,</span> <span class="n">h₃</span> <span class="o">:</span> <span class="n">y</span> <span class="bp">></span> <span class="n">x</span> <span class="bp">⊢</span> <span class="n">y</span> <span class="bp">≥</span> <span class="mi">4</span> </pre></div> </div> <p>The lines before the one that begins with <code class="docutils literal notranslate"><span class="pre">⊢</span></code> denote the <em>context</em>:
-
@@ -181,20 +177,20 @@ For example, <code class="docutils literal notranslate"><span class="pre">rw</spreplaces <code class="docutils literal notranslate"><span class="pre">a</span> <span class="pre">*</span> <span class="pre">(b</span> <span class="pre">*</span> <span class="pre">c)</span></code> by <code class="docutils literal notranslate"><span class="pre">a</span> <span class="pre">*</span> <span class="pre">b</span> <span class="pre">*</span> <span class="pre">c</span></code> in the current goal. Note that the left-pointing arrow refers to going from right to left in the identity provided by <code class="docutils literal notranslate"><span class="pre">mul_assoc</span></code>, it has nothing to do with the left or right side of the goal.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="n">c</span> <span class="bp">*</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">=</span> <span class="n">b</span> <span class="bp">*</span> <span class="o">(</span><span class="n">a</span> <span class="bp">*</span> <span class="n">c</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">*</span> <span class="o">(</span><span class="n">b</span> <span class="bp">*</span> <span class="n">c</span><span class="o">)</span> <span class="bp">=</span> <span class="n">b</span> <span class="bp">*</span> <span class="o">(</span><span class="n">a</span> <span class="bp">*</span> <span class="n">c</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>You can also use identities like <code class="docutils literal notranslate"><span class="pre">mul_assoc</span></code> and <code class="docutils literal notranslate"><span class="pre">mul_comm</span></code> without arguments. In this case, the rewrite tactic tries to match the left-hand side with an expression in the goal, using the first pattern it finds.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">mul_assoc</span><span class="o">]</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">mul_comm</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">c</span> <span class="bp">=</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">c</span> <span class="bp">*</span> <span class="n">a</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">mul_assoc</span><span class="o">]</span> <span class="n">rw</span> <span class="o">[</span><span class="n">mul_comm</span><span class="o">]</span> </pre></div> </div> <p>You can also provide <em>partial</em> information.
-
@@ -203,43 +199,43 @@ For example, <code class="docutils literal notranslate"><span class="pre">mul_coTry doing the first of these examples without providing any arguments at all, and the second with only one argument.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">c</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">*</span> <span class="o">(</span><span class="n">b</span> <span class="bp">*</span> <span class="n">c</span><span class="o">)</span> <span class="bp">=</span> <span class="n">b</span> <span class="bp">*</span> <span class="o">(</span><span class="n">c</span> <span class="bp">*</span> <span class="n">a</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">*</span> <span class="o">(</span><span class="n">b</span> <span class="bp">*</span> <span class="n">c</span><span class="o">)</span> <span class="bp">=</span> <span class="n">b</span> <span class="bp">*</span> <span class="o">(</span><span class="n">a</span> <span class="bp">*</span> <span class="n">c</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>You can also use <code class="docutils literal notranslate"><span class="pre">rw</span></code> with facts from the local context.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="n">e</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">d</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">e</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">e</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">d</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">h'</span><span class="o">]</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="bp">←</span><span class="w"> </span><span class="n">mul_assoc</span><span class="o">]</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">h</span><span class="o">]</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">mul_assoc</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="n">d</span> <span class="n">e</span> <span class="n">f</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">c</span> <span class="bp">*</span> <span class="n">d</span><span class="o">)</span> <span class="o">(</span><span class="n">h'</span> <span class="o">:</span> <span class="n">e</span> <span class="bp">=</span> <span class="n">f</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">*</span> <span class="o">(</span><span class="n">b</span> <span class="bp">*</span> <span class="n">e</span><span class="o">)</span> <span class="bp">=</span> <span class="n">c</span> <span class="bp">*</span> <span class="o">(</span><span class="n">d</span> <span class="bp">*</span> <span class="n">f</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">h'</span><span class="o">]</span> <span class="n">rw</span> <span class="o">[</span><span class="bp">←</span> <span class="n">mul_assoc</span><span class="o">]</span> <span class="n">rw</span> <span class="o">[</span><span class="n">h</span><span class="o">]</span> <span class="n">rw</span> <span class="o">[</span><span class="n">mul_assoc</span><span class="o">]</span> </pre></div> </div> <p>Try these, using the theorem <code class="docutils literal notranslate"><span class="pre">sub_self</span></code> for the second one:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="n">e</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">e</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">e</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="n">d</span> <span class="n">e</span> <span class="n">f</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">c</span> <span class="bp">=</span> <span class="n">e</span> <span class="bp">*</span> <span class="n">f</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">c</span> <span class="bp">*</span> <span class="n">d</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">e</span> <span class="bp">*</span> <span class="n">f</span> <span class="bp">*</span> <span class="n">d</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hyp</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">d</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hyp'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="n">d</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">hyp</span> <span class="o">:</span> <span class="n">c</span> <span class="bp">=</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">-</span> <span class="n">d</span><span class="o">)</span> <span class="o">(</span><span class="n">hyp'</span> <span class="o">:</span> <span class="n">d</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">b</span><span class="o">)</span> <span class="o">:</span> <span class="n">c</span> <span class="bp">=</span> <span class="mi">0</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>Multiple rewrite commands can be carried out with a single command, by listing the relevant identities separated by commas inside the square brackets.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="n">e</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">d</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">e</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">e</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">d</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">h'</span><span class="o">,</span><span class="w"> </span><span class="bp">←</span><span class="w"> </span><span class="n">mul_assoc</span><span class="o">,</span><span class="w"> </span><span class="n">h</span><span class="o">,</span><span class="w"> </span><span class="n">mul_assoc</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="n">d</span> <span class="n">e</span> <span class="n">f</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">c</span> <span class="bp">*</span> <span class="n">d</span><span class="o">)</span> <span class="o">(</span><span class="n">h'</span> <span class="o">:</span> <span class="n">e</span> <span class="bp">=</span> <span class="n">f</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">*</span> <span class="o">(</span><span class="n">b</span> <span class="bp">*</span> <span class="n">e</span><span class="o">)</span> <span class="bp">=</span> <span class="n">c</span> <span class="bp">*</span> <span class="o">(</span><span class="n">d</span> <span class="bp">*</span> <span class="n">f</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">h'</span><span class="o">,</span> <span class="bp">←</span> <span class="n">mul_assoc</span><span class="o">,</span> <span class="n">h</span><span class="o">,</span> <span class="n">mul_assoc</span><span class="o">]</span> </pre></div> </div> <p>You still see the incremental progress by placing the cursor after a comma in any list of rewrites.</p> <p>Another trick is that we can declare variables once and for all outside an example or theorem. Lean then includes them automatically.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="n">e</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="n">d</span> <span class="n">e</span> <span class="n">f</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">d</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">e</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">e</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">d</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">h'</span><span class="o">,</span><span class="w"> </span><span class="bp">←</span><span class="w"> </span><span class="n">mul_assoc</span><span class="o">,</span><span class="w"> </span><span class="n">h</span><span class="o">,</span><span class="w"> </span><span class="n">mul_assoc</span><span class="o">]</span> <span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">c</span> <span class="bp">*</span> <span class="n">d</span><span class="o">)</span> <span class="o">(</span><span class="n">h'</span> <span class="o">:</span> <span class="n">e</span> <span class="bp">=</span> <span class="n">f</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">*</span> <span class="o">(</span><span class="n">b</span> <span class="bp">*</span> <span class="n">e</span><span class="o">)</span> <span class="bp">=</span> <span class="n">c</span> <span class="bp">*</span> <span class="o">(</span><span class="n">d</span> <span class="bp">*</span> <span class="n">f</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">h'</span><span class="o">,</span> <span class="bp">←</span> <span class="n">mul_assoc</span><span class="o">,</span> <span class="n">h</span><span class="o">,</span> <span class="n">mul_assoc</span><span class="o">]</span> </pre></div> </div> <p>Inspection of the tactic state at the beginning of the above proof
-
@@ -249,16 +245,16 @@ in a <code class="docutils literal notranslate"><span class="pre">section</span>Finally, recall from the introduction that Lean provides us with a command to determine the type of an expression:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">section</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="n">a</span> <span class="k">#check</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="n">mul_comm</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">mul_comm</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="n">mul_assoc</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span> <span class="k">#check</span><span class="w"> </span><span class="n">mul_comm</span><span class="w"> </span><span class="n">a</span> <span class="k">#check</span><span class="w"> </span><span class="n">mul_comm</span> <span class="k">#check</span> <span class="n">a</span> <span class="k">#check</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">b</span> <span class="k">#check</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="k">#check</span> <span class="n">mul_comm</span> <span class="n">a</span> <span class="n">b</span> <span class="k">#check</span> <span class="o">(</span><span class="n">mul_comm</span> <span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">a</span><span class="o">)</span> <span class="k">#check</span> <span class="n">mul_assoc</span> <span class="n">c</span> <span class="n">a</span> <span class="n">b</span> <span class="k">#check</span> <span class="n">mul_comm</span> <span class="n">a</span> <span class="k">#check</span> <span class="n">mul_comm</span> <span class="kd">end</span> </pre></div>
-
@@ -278,10 +274,10 @@ that <code class="docutils literal notranslate"><span class="pre">2</span> <spanexpress the distributivity of multiplication over addition, and the theorem <code class="docutils literal notranslate"><span class="pre">add_assoc</span></code> expresses the associativity of addition. Use the <code class="docutils literal notranslate"><span class="pre">#check</span></code> command to see the precise statements.</p> <div class="highlight-lean notranslate" id="index-3"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">mul_add</span><span class="o">,</span><span class="w"> </span><span class="n">add_mul</span><span class="o">,</span><span class="w"> </span><span class="n">add_mul</span><span class="o">]</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="bp">←</span><span class="w"> </span><span class="n">add_assoc</span><span class="o">,</span><span class="w"> </span><span class="n">add_assoc</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="o">)]</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">mul_comm</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="bp">←</span><span class="w"> </span><span class="n">two_mul</span><span class="o">]</span> <div class="highlight-lean notranslate" id="index-3"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="bp">*</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">+</span> <span class="mi">2</span> <span class="bp">*</span> <span class="o">(</span><span class="n">a</span> <span class="bp">*</span> <span class="n">b</span><span class="o">)</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">b</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">mul_add</span><span class="o">,</span> <span class="n">add_mul</span><span class="o">,</span> <span class="n">add_mul</span><span class="o">]</span> <span class="n">rw</span> <span class="o">[</span><span class="bp">←</span> <span class="n">add_assoc</span><span class="o">,</span> <span class="n">add_assoc</span> <span class="o">(</span><span class="n">a</span> <span class="bp">*</span> <span class="n">a</span><span class="o">)]</span> <span class="n">rw</span> <span class="o">[</span><span class="n">mul_comm</span> <span class="n">b</span> <span class="n">a</span><span class="o">,</span> <span class="bp">←</span> <span class="n">two_mul</span><span class="o">]</span> </pre></div> </div> <p>Whereas it is possible to figure out what it going on in this proof
-
@@ -289,14 +285,14 @@ by stepping through it in the editor,it is hard to read on its own. Lean provides a more structured way of writing proofs like this using the <code class="docutils literal notranslate"><span class="pre">calc</span></code> keyword.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="k">calc</span> <span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">mul_add</span><span class="o">,</span><span class="w"> </span><span class="n">add_mul</span><span class="o">,</span><span class="w"> </span><span class="n">add_mul</span><span class="o">]</span> <span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="o">(</span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="bp">←</span><span class="w"> </span><span class="n">add_assoc</span><span class="o">,</span><span class="w"> </span><span class="n">add_assoc</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="o">)]</span> <span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">mul_comm</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="bp">←</span><span class="w"> </span><span class="n">two_mul</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="bp">*</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">+</span> <span class="mi">2</span> <span class="bp">*</span> <span class="o">(</span><span class="n">a</span> <span class="bp">*</span> <span class="n">b</span><span class="o">)</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">b</span> <span class="o">:=</span> <span class="k">calc</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="bp">*</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">+</span> <span class="o">(</span><span class="n">a</span> <span class="bp">*</span> <span class="n">b</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">b</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">mul_add</span><span class="o">,</span> <span class="n">add_mul</span><span class="o">,</span> <span class="n">add_mul</span><span class="o">]</span> <span class="n">_</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">+</span> <span class="o">(</span><span class="n">b</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">b</span><span class="o">)</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">b</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="bp">←</span> <span class="n">add_assoc</span><span class="o">,</span> <span class="n">add_assoc</span> <span class="o">(</span><span class="n">a</span> <span class="bp">*</span> <span class="n">a</span><span class="o">)]</span> <span class="n">_</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">+</span> <span class="mi">2</span> <span class="bp">*</span> <span class="o">(</span><span class="n">a</span> <span class="bp">*</span> <span class="n">b</span><span class="o">)</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">b</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">mul_comm</span> <span class="n">b</span> <span class="n">a</span><span class="o">,</span> <span class="bp">←</span> <span class="n">two_mul</span><span class="o">]</span> </pre></div> </div> <p>Notice that the proof does <em>not</em> begin with <code class="docutils literal notranslate"><span class="pre">by</span></code>:
-
@@ -313,44 +309,44 @@ try changing the indentation in the proof above to see what happens.</p>using the <code class="docutils literal notranslate"><span class="pre">sorry</span></code> tactic for justification, make sure Lean accepts the expression modulo these, and then justify the individual steps using tactics.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="k">calc</span> <span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="o">(</span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="bp">*</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">+</span> <span class="mi">2</span> <span class="bp">*</span> <span class="o">(</span><span class="n">a</span> <span class="bp">*</span> <span class="n">b</span><span class="o">)</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">b</span> <span class="o">:=</span> <span class="k">calc</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="bp">*</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">+</span> <span class="o">(</span><span class="n">a</span> <span class="bp">*</span> <span class="n">b</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">b</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="n">_</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">+</span> <span class="o">(</span><span class="n">b</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">b</span><span class="o">)</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">b</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="n">_</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">+</span> <span class="mi">2</span> <span class="bp">*</span> <span class="o">(</span><span class="n">a</span> <span class="bp">*</span> <span class="n">b</span><span class="o">)</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">b</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>Try proving the following identity using both a pure <code class="docutils literal notranslate"><span class="pre">rw</span></code> proof and a more structured <code class="docutils literal notranslate"><span class="pre">calc</span></code> proof:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">c</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">d</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="bp">*</span> <span class="o">(</span><span class="n">c</span> <span class="bp">+</span> <span class="n">d</span><span class="o">)</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">c</span> <span class="bp">+</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">d</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">c</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">d</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>The following exercise is a little more challenging. You can use the theorems listed underneath.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="bp">*</span> <span class="o">(</span><span class="n">a</span> <span class="bp">-</span> <span class="n">b</span><span class="o">)</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">-</span> <span class="n">b</span> <span class="bp">^</span> <span class="mi">2</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="k">#check</span><span class="w"> </span><span class="n">pow_two</span><span class="w"> </span><span class="n">a</span> <span class="k">#check</span><span class="w"> </span><span class="n">mul_sub</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span> <span class="k">#check</span><span class="w"> </span><span class="n">add_mul</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span> <span class="k">#check</span><span class="w"> </span><span class="n">add_sub</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span> <span class="k">#check</span><span class="w"> </span><span class="n">sub_sub</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span> <span class="k">#check</span><span class="w"> </span><span class="n">add_zero</span><span class="w"> </span><span class="n">a</span> <span class="k">#check</span> <span class="n">pow_two</span> <span class="n">a</span> <span class="k">#check</span> <span class="n">mul_sub</span> <span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="k">#check</span> <span class="n">add_mul</span> <span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="k">#check</span> <span class="n">add_sub</span> <span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="k">#check</span> <span class="n">sub_sub</span> <span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="k">#check</span> <span class="n">add_zero</span> <span class="n">a</span> </pre></div> </div> <p id="index-4">We can also perform rewriting in an assumption in the context. For example, <code class="docutils literal notranslate"><span class="pre">rw</span> <span class="pre">[mul_comm</span> <span class="pre">a</span> <span class="pre">b]</span> <span class="pre">at</span> <span class="pre">hyp</span></code> replaces <code class="docutils literal notranslate"><span class="pre">a</span> <span class="pre">*</span> <span class="pre">b</span></code> by <code class="docutils literal notranslate"><span class="pre">b</span> <span class="pre">*</span> <span class="pre">a</span></code> in the assumption <code class="docutils literal notranslate"><span class="pre">hyp</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hyp</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hyp'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">d</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">hyp'</span><span class="o">]</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">hyp</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">mul_comm</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="n">a</span><span class="o">]</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">hyp</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="bp">←</span><span class="w"> </span><span class="n">two_mul</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">d</span><span class="o">)]</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">hyp</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="bp">←</span><span class="w"> </span><span class="n">mul_assoc</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">d</span><span class="o">]</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">hyp</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">hyp</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="n">d</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">hyp</span> <span class="o">:</span> <span class="n">c</span> <span class="bp">=</span> <span class="n">d</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="o">(</span><span class="n">hyp'</span> <span class="o">:</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">d</span><span class="o">)</span> <span class="o">:</span> <span class="n">c</span> <span class="bp">=</span> <span class="mi">2</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">d</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">hyp'</span><span class="o">]</span> <span class="n">at</span> <span class="n">hyp</span> <span class="n">rw</span> <span class="o">[</span><span class="n">mul_comm</span> <span class="n">d</span> <span class="n">a</span><span class="o">]</span> <span class="n">at</span> <span class="n">hyp</span> <span class="n">rw</span> <span class="o">[</span><span class="bp">←</span> <span class="n">two_mul</span> <span class="o">(</span><span class="n">a</span> <span class="bp">*</span> <span class="n">d</span><span class="o">)]</span> <span class="n">at</span> <span class="n">hyp</span> <span class="n">rw</span> <span class="o">[</span><span class="bp">←</span> <span class="n">mul_assoc</span> <span class="mi">2</span> <span class="n">a</span> <span class="n">d</span><span class="o">]</span> <span class="n">at</span> <span class="n">hyp</span> <span class="n">exact</span> <span class="n">hyp</span> </pre></div> </div> <p id="index-5">In the last step, the <code class="docutils literal notranslate"><span class="pre">exact</span></code> tactic can use <code class="docutils literal notranslate"><span class="pre">hyp</span></code> to solve the goal
-
@@ -359,18 +355,18 @@ because at that point <code class="docutils literal notranslate"><span class="pruseful bit of automation with a <code class="docutils literal notranslate"><span class="pre">ring</span></code> tactic, which is designed to prove identities in any commutative ring as long as they follow purely from the ring axioms, without using any local assumption.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">ring</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">c</span> <span class="bp">*</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">=</span> <span class="n">b</span> <span class="bp">*</span> <span class="o">(</span><span class="n">a</span> <span class="bp">*</span> <span class="n">c</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">ring</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">ring</span> <span class="kd">example</span> <span class="o">:</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="bp">*</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">+</span> <span class="mi">2</span> <span class="bp">*</span> <span class="o">(</span><span class="n">a</span> <span class="bp">*</span> <span class="n">b</span><span class="o">)</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">b</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">ring</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">ring</span> <span class="kd">example</span> <span class="o">:</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="bp">*</span> <span class="o">(</span><span class="n">a</span> <span class="bp">-</span> <span class="n">b</span><span class="o">)</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">-</span> <span class="n">b</span> <span class="bp">^</span> <span class="mi">2</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">ring</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">hyp</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hyp'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">d</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">hyp</span><span class="o">,</span><span class="w"> </span><span class="n">hyp'</span><span class="o">]</span> <span class="w"> </span><span class="n">ring</span> <span class="kd">example</span> <span class="o">(</span><span class="n">hyp</span> <span class="o">:</span> <span class="n">c</span> <span class="bp">=</span> <span class="n">d</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="o">(</span><span class="n">hyp'</span> <span class="o">:</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">d</span><span class="o">)</span> <span class="o">:</span> <span class="n">c</span> <span class="bp">=</span> <span class="mi">2</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">d</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">hyp</span><span class="o">,</span> <span class="n">hyp'</span><span class="o">]</span> <span class="n">ring</span> </pre></div> </div> <p>The <code class="docutils literal notranslate"><span class="pre">ring</span></code> tactic is imported indirectly when we
-
@@ -385,14 +381,14 @@ structures.</p>Possible matches are enumerated starting with 1, so in the following example, <code class="docutils literal notranslate"><span class="pre">nth_rw</span> <span class="pre">2</span> <span class="pre">[h]</span></code> replaces the second occurrence of <code class="docutils literal notranslate"><span class="pre">a</span> <span class="pre">+</span> <span class="pre">b</span></code> with <code class="docutils literal notranslate"><span class="pre">c</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">c</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">nth_rw</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">[</span><span class="n">h</span><span class="o">]</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">add_mul</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">c</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="bp">*</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">c</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">c</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">nth_rw</span> <span class="mi">2</span> <span class="o">[</span><span class="n">h</span><span class="o">]</span> <span class="n">rw</span> <span class="o">[</span><span class="n">add_mul</span><span class="o">]</span> </pre></div> </div> </section> <section id="proving-identities-in-algebraic-structures"> <span id="id2"></span><h2><span class="section-number">2.2. </span>Proving Identities in Algebraic Structures<a class="headerlink" href="#proving-identities-in-algebraic-structures" title="Link to this heading"></a></h2> <span id="id2"></span><h2><span class="section-number">2.2. </span>Proving Identities in Algebraic Structures<a class="headerlink" href="#proving-identities-in-algebraic-structures" title="Permalink to this heading"></a></h2> <p id="index-7">Mathematically, a ring consists of a collection of objects, <span class="math notranslate nohighlight">\(R\)</span>, operations <span class="math notranslate nohighlight">\(+\)</span> <span class="math notranslate nohighlight">\(\times\)</span>, and constants <span class="math notranslate nohighlight">\(0\)</span> and <span class="math notranslate nohighlight">\(1\)</span>, and an operation <span class="math notranslate nohighlight">\(x \mapsto -x\)</span> such that:</p>
-
@@ -404,17 +400,17 @@ and multiplication distributes over addition.</p></li></ul> <p>In Lean, the collection of objects is represented as a <em>type</em>, <code class="docutils literal notranslate"><span class="pre">R</span></code>. The ring axioms are as follows:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">R</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">Ring</span><span class="w"> </span><span class="n">R</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">(</span><span class="n">R</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">)</span> <span class="o">[</span><span class="n">Ring</span> <span class="n">R</span><span class="o">]</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">add_assoc</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="o">(</span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">c</span><span class="o">))</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">add_comm</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">a</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">zero_add</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">,</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">neg_add_cancel</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">,</span><span class="w"> </span><span class="bp">-</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">mul_assoc</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="o">))</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">mul_one</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">one_mul</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">,</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">mul_add</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">c</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">add_mul</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">,</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">add_assoc</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">R</span><span class="o">,</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">+</span> <span class="n">c</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">+</span> <span class="o">(</span><span class="n">b</span> <span class="bp">+</span> <span class="n">c</span><span class="o">))</span> <span class="k">#check</span> <span class="o">(</span><span class="n">add_comm</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">R</span><span class="o">,</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">b</span> <span class="bp">+</span> <span class="n">a</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">zero_add</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span> <span class="o">:</span> <span class="n">R</span><span class="o">,</span> <span class="mi">0</span> <span class="bp">+</span> <span class="n">a</span> <span class="bp">=</span> <span class="n">a</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">neg_add_cancel</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span> <span class="o">:</span> <span class="n">R</span><span class="o">,</span> <span class="bp">-</span><span class="n">a</span> <span class="bp">+</span> <span class="n">a</span> <span class="bp">=</span> <span class="mi">0</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">mul_assoc</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">R</span><span class="o">,</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">c</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">*</span> <span class="o">(</span><span class="n">b</span> <span class="bp">*</span> <span class="n">c</span><span class="o">))</span> <span class="k">#check</span> <span class="o">(</span><span class="n">mul_one</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span> <span class="o">:</span> <span class="n">R</span><span class="o">,</span> <span class="n">a</span> <span class="bp">*</span> <span class="mi">1</span> <span class="bp">=</span> <span class="n">a</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">one_mul</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span> <span class="o">:</span> <span class="n">R</span><span class="o">,</span> <span class="mi">1</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">=</span> <span class="n">a</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">mul_add</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">R</span><span class="o">,</span> <span class="n">a</span> <span class="bp">*</span> <span class="o">(</span><span class="n">b</span> <span class="bp">+</span> <span class="n">c</span><span class="o">)</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">b</span> <span class="bp">+</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">c</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">add_mul</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">R</span><span class="o">,</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="bp">*</span> <span class="n">c</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">c</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">c</span><span class="o">)</span> </pre></div> </div> <p>You will learn more about the square brackets in the first line later,
-
@@ -451,18 +447,18 @@ form a ring in which commutativity usually fails. If we declare <code class="doc<em>commutative</em> ring, in fact, all the theorems in the last section continue to hold when we replace <code class="docutils literal notranslate"><span class="pre">ℝ</span></code> by <code class="docutils literal notranslate"><span class="pre">R</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">R</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">CommRing</span><span class="w"> </span><span class="n">R</span><span class="o">]</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">(</span><span class="n">R</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">)</span> <span class="o">[</span><span class="n">CommRing</span> <span class="n">R</span><span class="o">]</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="n">d</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">ring</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">c</span> <span class="bp">*</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">=</span> <span class="n">b</span> <span class="bp">*</span> <span class="o">(</span><span class="n">a</span> <span class="bp">*</span> <span class="n">c</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">ring</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">ring</span> <span class="kd">example</span> <span class="o">:</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="bp">*</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">+</span> <span class="mi">2</span> <span class="bp">*</span> <span class="o">(</span><span class="n">a</span> <span class="bp">*</span> <span class="n">b</span><span class="o">)</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">b</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">ring</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">ring</span> <span class="kd">example</span> <span class="o">:</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="bp">*</span> <span class="o">(</span><span class="n">a</span> <span class="bp">-</span> <span class="n">b</span><span class="o">)</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">-</span> <span class="n">b</span> <span class="bp">^</span> <span class="mi">2</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">ring</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">hyp</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hyp'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">d</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">hyp</span><span class="o">,</span><span class="w"> </span><span class="n">hyp'</span><span class="o">]</span> <span class="w"> </span><span class="n">ring</span> <span class="kd">example</span> <span class="o">(</span><span class="n">hyp</span> <span class="o">:</span> <span class="n">c</span> <span class="bp">=</span> <span class="n">d</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="o">(</span><span class="n">hyp'</span> <span class="o">:</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">d</span><span class="o">)</span> <span class="o">:</span> <span class="n">c</span> <span class="bp">=</span> <span class="mi">2</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">d</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">hyp</span><span class="o">,</span> <span class="n">hyp'</span><span class="o">]</span> <span class="n">ring</span> </pre></div> </div> <p>We leave it to you to check that all the other proofs go through unchanged.
-
@@ -491,17 +487,17 @@ in the next example we put our versions of the librarytheorems in a new namespace called <code class="docutils literal notranslate"><span class="pre">MyRing.</span></code></p> <p>The next example shows that we do not need <code class="docutils literal notranslate"><span class="pre">add_zero</span></code> or <code class="docutils literal notranslate"><span class="pre">add_right_neg</span></code> as ring axioms, because they follow from the other axioms.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">namespace</span><span class="w"> </span><span class="n">MyRing</span> <span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">R</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Ring</span><span class="w"> </span><span class="n">R</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">namespace</span> <span class="n">MyRing</span> <span class="kd">variable</span> <span class="o">{</span><span class="n">R</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Ring</span> <span class="n">R</span><span class="o">]</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">add_zero</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">add_comm</span><span class="o">,</span><span class="w"> </span><span class="n">zero_add</span><span class="o">]</span> <span class="kd">theorem</span> <span class="n">add_zero</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">+</span> <span class="mi">0</span> <span class="bp">=</span> <span class="n">a</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">add_comm</span><span class="o">,</span> <span class="n">zero_add</span><span class="o">]</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">add_right_neg</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="bp">-</span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">add_comm</span><span class="o">,</span><span class="w"> </span><span class="n">neg_add_cancel</span><span class="o">]</span> <span class="kd">theorem</span> <span class="n">add_right_neg</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">+</span> <span class="bp">-</span><span class="n">a</span> <span class="bp">=</span> <span class="mi">0</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">add_comm</span><span class="o">,</span> <span class="n">neg_add_cancel</span><span class="o">]</span> <span class="k">#check</span><span class="w"> </span><span class="n">MyRing.add_zero</span> <span class="k">#check</span><span class="w"> </span><span class="n">add_zero</span> <span class="k">#check</span> <span class="n">MyRing.add_zero</span> <span class="k">#check</span> <span class="n">add_zero</span> <span class="kd">end</span><span class="w"> </span><span class="n">MyRing</span> <span class="kd">end</span> <span class="n">MyRing</span> </pre></div> </div> <p>The net effect is that we can temporarily reprove a theorem in the library,
-
@@ -516,21 +512,21 @@ This declares <code class="docutils literal notranslate"><span class="pre">R</spWe will explain what this means in a moment, but don’t worry about it in the meanwhile.)</p> <p>Here is a useful theorem:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">neg_add_cancel_left</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">-</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="bp">←</span><span class="w"> </span><span class="n">add_assoc</span><span class="o">,</span><span class="w"> </span><span class="n">neg_add_cancel</span><span class="o">,</span><span class="w"> </span><span class="n">zero_add</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">neg_add_cancel_left</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="o">:</span> <span class="bp">-</span><span class="n">a</span> <span class="bp">+</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="bp">=</span> <span class="n">b</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="bp">←</span> <span class="n">add_assoc</span><span class="o">,</span> <span class="n">neg_add_cancel</span><span class="o">,</span> <span class="n">zero_add</span><span class="o">]</span> </pre></div> </div> <p>Prove the companion version:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">add_neg_cancel_right</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="bp">-</span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">add_neg_cancel_right</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">+</span> <span class="bp">-</span><span class="n">b</span> <span class="bp">=</span> <span class="n">a</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>Use these to prove the following:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">add_left_cancel</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">c</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">add_left_cancel</span> <span class="o">{</span><span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">R</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">c</span><span class="o">)</span> <span class="o">:</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">c</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">add_right_cancel</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">theorem</span> <span class="n">add_right_cancel</span> <span class="o">{</span><span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">R</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">c</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">=</span> <span class="n">c</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>With enough planning, you can do each of them with three rewrites.</p>
-
@@ -558,10 +554,10 @@ So, given the statement of the theorem above,the correct expression is simply <code class="docutils literal notranslate"><span class="pre">add_left_cancel</span> <span class="pre">h</span></code>.</p> <p>To illustrate, let us show that <code class="docutils literal notranslate"><span class="pre">a</span> <span class="pre">*</span> <span class="pre">0</span> <span class="pre">=</span> <span class="pre">0</span></code> follows from the ring axioms.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">mul_zero</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="bp">←</span><span class="w"> </span><span class="n">mul_add</span><span class="o">,</span><span class="w"> </span><span class="n">add_zero</span><span class="o">,</span><span class="w"> </span><span class="n">add_zero</span><span class="o">]</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">add_left_cancel</span><span class="w"> </span><span class="n">h</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">mul_zero</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">*</span> <span class="mi">0</span> <span class="bp">=</span> <span class="mi">0</span> <span class="o">:=</span> <span class="kd">by</span> <span class="k">have</span> <span class="n">h</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">*</span> <span class="mi">0</span> <span class="bp">+</span> <span class="n">a</span> <span class="bp">*</span> <span class="mi">0</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">*</span> <span class="mi">0</span> <span class="bp">+</span> <span class="mi">0</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="bp">←</span> <span class="n">mul_add</span><span class="o">,</span> <span class="n">add_zero</span><span class="o">,</span> <span class="n">add_zero</span><span class="o">]</span> <span class="n">rw</span> <span class="o">[</span><span class="n">add_left_cancel</span> <span class="n">h</span><span class="o">]</span> </pre></div> </div> <p id="index-11">We have used a new trick!
-
@@ -591,26 +587,26 @@ than <code class="docutils literal notranslate"><span class="pre">apply</span></human readers and easier to maintain when the library evolves.</p> <p>Remember that multiplication is not assumed to be commutative, so the following theorem also requires some work.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">zero_mul</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">zero_mul</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">=</span> <span class="mi">0</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>By now, you should also be able replace each <code class="docutils literal notranslate"><span class="pre">sorry</span></code> in the next exercise with a proof, still using only facts about rings that we have established in this section.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">neg_eq_of_add_eq_zero</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">-</span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">neg_eq_of_add_eq_zero</span> <span class="o">{</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">R</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">=</span> <span class="mi">0</span><span class="o">)</span> <span class="o">:</span> <span class="bp">-</span><span class="n">a</span> <span class="bp">=</span> <span class="n">b</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">eq_neg_of_add_eq_zero</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">-</span><span class="n">b</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">theorem</span> <span class="n">eq_neg_of_add_eq_zero</span> <span class="o">{</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">R</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">=</span> <span class="mi">0</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">=</span> <span class="bp">-</span><span class="n">b</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">neg_zero</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="bp">-</span><span class="mi">0</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">neg_eq_of_add_eq_zero</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">add_zero</span><span class="o">]</span> <span class="kd">theorem</span> <span class="n">neg_zero</span> <span class="o">:</span> <span class="o">(</span><span class="bp">-</span><span class="mi">0</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="bp">=</span> <span class="mi">0</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">apply</span> <span class="n">neg_eq_of_add_eq_zero</span> <span class="n">rw</span> <span class="o">[</span><span class="n">add_zero</span><span class="o">]</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">neg_neg</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="bp">-</span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">theorem</span> <span class="n">neg_neg</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="o">:</span> <span class="bp">-</span> <span class="bp">-</span><span class="n">a</span> <span class="bp">=</span> <span class="n">a</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>We had to use the annotation <code class="docutils literal notranslate"><span class="pre">(-0</span> <span class="pre">:</span> <span class="pre">R)</span></code> instead of <code class="docutils literal notranslate"><span class="pre">0</span></code> in the third theorem
-
@@ -619,16 +615,16 @@ it is impossible for Lean to infer which <code class="docutils literal notranslaand by default it would be interpreted as a natural number.</p> <p>In Lean, subtraction in a ring is provably equal to addition of the additive inverse.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="bp">-</span><span class="n">b</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">sub_eq_add_neg</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">-</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">+</span> <span class="bp">-</span><span class="n">b</span> <span class="o">:=</span> <span class="n">sub_eq_add_neg</span> <span class="n">a</span> <span class="n">b</span> </pre></div> </div> <p>On the real numbers, it is <em>defined</em> that way:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="bp">-</span><span class="n">b</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">-</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">+</span> <span class="bp">-</span><span class="n">b</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="bp">-</span><span class="n">b</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">example</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">-</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">+</span> <span class="bp">-</span><span class="n">b</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rfl</span> </pre></div> </div> <p id="index-13">The proof term <code class="docutils literal notranslate"><span class="pre">rfl</span></code> is short for “reflexivity”.
-
@@ -643,8 +639,8 @@ but in some contexts, when dealing with the real numbers,you can use the two sides of the equation interchangeably. For example, you now have enough information to prove the theorem <code class="docutils literal notranslate"><span class="pre">self_sub</span></code> from the last section:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">self_sub</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">self_sub</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">-</span> <span class="n">a</span> <span class="bp">=</span> <span class="mi">0</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>Show that you can prove this using <code class="docutils literal notranslate"><span class="pre">rw</span></code>,
-
@@ -655,11 +651,11 @@ using either <code class="docutils literal notranslate"><span class="pre">apply<With a bit of effort, you can use that to prove the theorem <code class="docutils literal notranslate"><span class="pre">two_mul</span></code> from the last section:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">one_add_one_eq_two</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">(</span><span class="mi">2</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">norm_num</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">one_add_one_eq_two</span> <span class="o">:</span> <span class="mi">1</span> <span class="bp">+</span> <span class="mi">1</span> <span class="bp">=</span> <span class="o">(</span><span class="mi">2</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">norm_num</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">two_mul</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">theorem</span> <span class="n">two_mul</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="o">:</span> <span class="mi">2</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">a</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p id="index-14">We close this section by noting that some of the facts about
-
@@ -667,11 +663,11 @@ addition and negation that we established above do notneed the full strength of the ring axioms, or even commutativity of addition. The weaker notion of a <em>group</em> can be axiomatized as follows:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">A</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">AddGroup</span><span class="w"> </span><span class="n">A</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">(</span><span class="n">A</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">)</span> <span class="o">[</span><span class="n">AddGroup</span> <span class="n">A</span><span class="o">]</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">add_assoc</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">A</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="o">(</span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">c</span><span class="o">))</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">zero_add</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">A</span><span class="o">,</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">neg_add_cancel</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">A</span><span class="o">,</span><span class="w"> </span><span class="bp">-</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">add_assoc</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">A</span><span class="o">,</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">+</span> <span class="n">c</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">+</span> <span class="o">(</span><span class="n">b</span> <span class="bp">+</span> <span class="n">c</span><span class="o">))</span> <span class="k">#check</span> <span class="o">(</span><span class="n">zero_add</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span> <span class="o">:</span> <span class="n">A</span><span class="o">,</span> <span class="mi">0</span> <span class="bp">+</span> <span class="n">a</span> <span class="bp">=</span> <span class="n">a</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">neg_add_cancel</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span> <span class="o">:</span> <span class="n">A</span><span class="o">,</span> <span class="bp">-</span><span class="n">a</span> <span class="bp">+</span> <span class="n">a</span> <span class="bp">=</span> <span class="mi">0</span><span class="o">)</span> </pre></div> </div> <p>It is conventional to use additive notation when
-
@@ -680,25 +676,25 @@ and multiplicative notation otherwise.So Lean defines a multiplicative version as well as the additive version (and also their abelian variants, <code class="docutils literal notranslate"><span class="pre">AddCommGroup</span></code> and <code class="docutils literal notranslate"><span class="pre">CommGroup</span></code>).</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">mul_assoc</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="o">))</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">one_mul</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="o">,</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">inv_mul_cancel</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="bp">⁻¹</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">mul_assoc</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">G</span><span class="o">,</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">c</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">*</span> <span class="o">(</span><span class="n">b</span> <span class="bp">*</span> <span class="n">c</span><span class="o">))</span> <span class="k">#check</span> <span class="o">(</span><span class="n">one_mul</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span> <span class="o">:</span> <span class="n">G</span><span class="o">,</span> <span class="mi">1</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">=</span> <span class="n">a</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">inv_mul_cancel</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span> <span class="o">:</span> <span class="n">G</span><span class="o">,</span> <span class="n">a</span><span class="bp">⁻¹</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">=</span> <span class="mi">1</span><span class="o">)</span> </pre></div> </div> <p>If you are feeling cocky, try proving the following facts about groups, using only these axioms. You will need to prove a number of helper lemmas along the way. The proofs we have carried out in this section provide some hints.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">mul_inv_cancel</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="bp">⁻¹</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">mul_inv_cancel</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">G</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">a</span><span class="bp">⁻¹</span> <span class="bp">=</span> <span class="mi">1</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">mul_one</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">theorem</span> <span class="n">mul_one</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">G</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">*</span> <span class="mi">1</span> <span class="bp">=</span> <span class="n">a</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">mul_inv_rev</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="bp">⁻¹</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">b</span><span class="bp">⁻¹</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="bp">⁻¹</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">theorem</span> <span class="n">mul_inv_rev</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">G</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">a</span> <span class="bp">*</span> <span class="n">b</span><span class="o">)</span><span class="bp">⁻¹</span> <span class="bp">=</span> <span class="n">b</span><span class="bp">⁻¹</span> <span class="bp">*</span> <span class="n">a</span><span class="bp">⁻¹</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p id="index-15">Explicitly invoking those lemmas is tedious, so Mathlib provides
-
@@ -712,7 +708,7 @@ but also for the convenience of using a shorter name for thetactic that deals with commutative rings, since it is used more often.</p> </section> <section id="using-theorems-and-lemmas"> <span id="id3"></span><h2><span class="section-number">2.3. </span>Using Theorems and Lemmas<a class="headerlink" href="#using-theorems-and-lemmas" title="Link to this heading"></a></h2> <span id="id3"></span><h2><span class="section-number">2.3. </span>Using Theorems and Lemmas<a class="headerlink" href="#using-theorems-and-lemmas" title="Permalink to this heading"></a></h2> <p id="index-16">Rewriting is great for proving equations, but what about other sorts of theorems? For example, how can we prove an inequality,
-
@@ -721,8 +717,8 @@ We have already seen that theorems can be applied to arguments and hypotheses,and that the <code class="docutils literal notranslate"><span class="pre">apply</span></code> and <code class="docutils literal notranslate"><span class="pre">exact</span></code> tactics can be used to solve goals. In this section, we will make good use of these tools.</p> <p>Consider the library theorems <code class="docutils literal notranslate"><span class="pre">le_refl</span></code> and <code class="docutils literal notranslate"><span class="pre">le_trans</span></code>:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">le_refl</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">a</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">le_trans</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">c</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="o">(</span><span class="n">le_refl</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">,</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">a</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">le_trans</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">b</span> <span class="bp">→</span> <span class="n">b</span> <span class="bp">≤</span> <span class="n">c</span> <span class="bp">→</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">c</span><span class="o">)</span> </pre></div> </div> <p>As we explain in more detail in <a class="reference internal" href="C03_Logic.html#implication-and-the-universal-quantifier"><span class="std std-numref">Section 3.1</span></a>,
-
@@ -735,13 +731,13 @@ Rather, it expects to infer them from the context in which they are used.For example, when hypotheses <code class="docutils literal notranslate"><span class="pre">h</span> <span class="pre">:</span> <span class="pre">a</span> <span class="pre">≤</span> <span class="pre">b</span></code> and <code class="docutils literal notranslate"><span class="pre">h'</span> <span class="pre">:</span> <span class="pre">b</span> <span class="pre">≤</span> <span class="pre">c</span></code> are in the context, all the following work:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">c</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">b</span><span class="o">)</span> <span class="o">(</span><span class="n">h'</span> <span class="o">:</span> <span class="n">b</span> <span class="bp">≤</span> <span class="n">c</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">le_refl</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Real</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">a</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">le_refl</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">a</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">le_trans</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">c</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">le_trans</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">c</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">le_trans</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="n">h'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">c</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">le_refl</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span> <span class="o">:</span> <span class="n">Real</span><span class="o">,</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">a</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">le_refl</span> <span class="n">a</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">a</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">le_trans</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">b</span> <span class="bp">→</span> <span class="n">b</span> <span class="bp">≤</span> <span class="n">c</span> <span class="bp">→</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">c</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">le_trans</span> <span class="n">h</span> <span class="o">:</span> <span class="n">b</span> <span class="bp">≤</span> <span class="n">c</span> <span class="bp">→</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">c</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">le_trans</span> <span class="n">h</span> <span class="n">h'</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">c</span><span class="o">)</span> </pre></div> </div> <p id="index-17">The <code class="docutils literal notranslate"><span class="pre">apply</span></code> tactic takes a proof of a general statement or implication,
-
@@ -751,23 +747,23 @@ If the given proof matches the goal exactly(modulo <em>definitional</em> equality), you can use the <code class="docutils literal notranslate"><span class="pre">exact</span></code> tactic instead of <code class="docutils literal notranslate"><span class="pre">apply</span></code>. So, all of these work:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h₀</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h₁</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">z</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">le_trans</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">h₀</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">h₁</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="n">z</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">h₀</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">y</span><span class="o">)</span> <span class="o">(</span><span class="n">h₁</span> <span class="o">:</span> <span class="n">y</span> <span class="bp">≤</span> <span class="n">z</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">z</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">apply</span> <span class="n">le_trans</span> <span class="bp">·</span> <span class="n">apply</span> <span class="n">h₀</span> <span class="bp">·</span> <span class="n">apply</span> <span class="n">h₁</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h₀</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h₁</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">z</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">le_trans</span><span class="w"> </span><span class="n">h₀</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">h₁</span> <span class="kd">example</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="n">z</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">h₀</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">y</span><span class="o">)</span> <span class="o">(</span><span class="n">h₁</span> <span class="o">:</span> <span class="n">y</span> <span class="bp">≤</span> <span class="n">z</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">z</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">apply</span> <span class="n">le_trans</span> <span class="n">h₀</span> <span class="n">apply</span> <span class="n">h₁</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h₀</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h₁</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">z</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">le_trans</span><span class="w"> </span><span class="n">h₀</span><span class="w"> </span><span class="n">h₁</span> <span class="kd">example</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="n">z</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">h₀</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">y</span><span class="o">)</span> <span class="o">(</span><span class="n">h₁</span> <span class="o">:</span> <span class="n">y</span> <span class="bp">≤</span> <span class="n">z</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">z</span> <span class="o">:=</span> <span class="n">le_trans</span> <span class="n">h₀</span> <span class="n">h₁</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">le_refl</span> <span class="kd">example</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">apply</span> <span class="n">le_refl</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">le_refl</span><span class="w"> </span><span class="n">x</span> <span class="kd">example</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">x</span> <span class="o">:=</span> <span class="n">le_refl</span> <span class="n">x</span> </pre></div> </div> <p>In the first example, applying <code class="docutils literal notranslate"><span class="pre">le_trans</span></code>
-
@@ -778,30 +774,30 @@ within the block introduced by the dot, only one goal is visible,and it must be completed before the end of the block. Here we end the first block by starting a new one with another dot. We could just as well have decreased the indentation. In the fourth example and in the last example, In the third example and in the last example, we avoid going into tactic mode entirely: <code class="docutils literal notranslate"><span class="pre">le_trans</span> <span class="pre">h₀</span> <span class="pre">h₁</span></code> and <code class="docutils literal notranslate"><span class="pre">le_refl</span> <span class="pre">x</span></code> are the proof terms we need.</p> <p>Here are a few more library theorems:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">le_refl</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">a</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">le_trans</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">c</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">lt_of_le_of_lt</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">c</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">lt_of_lt_of_le</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">c</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">lt_trans</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">c</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="o">(</span><span class="n">le_refl</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span><span class="o">,</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">a</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">le_trans</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">b</span> <span class="bp">→</span> <span class="n">b</span> <span class="bp">≤</span> <span class="n">c</span> <span class="bp">→</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">c</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">lt_of_le_of_lt</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">b</span> <span class="bp">→</span> <span class="n">b</span> <span class="bp"><</span> <span class="n">c</span> <span class="bp">→</span> <span class="n">a</span> <span class="bp"><</span> <span class="n">c</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">lt_of_lt_of_le</span> <span class="o">:</span> <span class="n">a</span> <span class="bp"><</span> <span class="n">b</span> <span class="bp">→</span> <span class="n">b</span> <span class="bp">≤</span> <span class="n">c</span> <span class="bp">→</span> <span class="n">a</span> <span class="bp"><</span> <span class="n">c</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">lt_trans</span> <span class="o">:</span> <span class="n">a</span> <span class="bp"><</span> <span class="n">b</span> <span class="bp">→</span> <span class="n">b</span> <span class="bp"><</span> <span class="n">c</span> <span class="bp">→</span> <span class="n">a</span> <span class="bp"><</span> <span class="n">c</span><span class="o">)</span> </pre></div> </div> <p>Use them together with <code class="docutils literal notranslate"><span class="pre">apply</span></code> and <code class="docutils literal notranslate"><span class="pre">exact</span></code> to prove the following:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h₀</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h₁</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">c</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h₂</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">d</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h₃</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">e</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">e</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">h₀</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">b</span><span class="o">)</span> <span class="o">(</span><span class="n">h₁</span> <span class="o">:</span> <span class="n">b</span> <span class="bp"><</span> <span class="n">c</span><span class="o">)</span> <span class="o">(</span><span class="n">h₂</span> <span class="o">:</span> <span class="n">c</span> <span class="bp">≤</span> <span class="n">d</span><span class="o">)</span> <span class="o">(</span><span class="n">h₃</span> <span class="o">:</span> <span class="n">d</span> <span class="bp"><</span> <span class="n">e</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp"><</span> <span class="n">e</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p id="index-18">In fact, Lean has a tactic that does this sort of thing automatically:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h₀</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h₁</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">c</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h₂</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">d</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h₃</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">e</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">e</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">linarith</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">h₀</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">b</span><span class="o">)</span> <span class="o">(</span><span class="n">h₁</span> <span class="o">:</span> <span class="n">b</span> <span class="bp"><</span> <span class="n">c</span><span class="o">)</span> <span class="o">(</span><span class="n">h₂</span> <span class="o">:</span> <span class="n">c</span> <span class="bp">≤</span> <span class="n">d</span><span class="o">)</span> <span class="o">(</span><span class="n">h₃</span> <span class="o">:</span> <span class="n">d</span> <span class="bp"><</span> <span class="n">e</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp"><</span> <span class="n">e</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">linarith</span> </pre></div> </div> <p>The <code class="docutils literal notranslate"><span class="pre">linarith</span></code> tactic is designed to handle <em>linear arithmetic</em>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h''</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">linarith</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="mi">2</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">≤</span> <span class="mi">3</span> <span class="bp">*</span> <span class="n">b</span><span class="o">)</span> <span class="o">(</span><span class="n">h'</span> <span class="o">:</span> <span class="mi">1</span> <span class="bp">≤</span> <span class="n">a</span><span class="o">)</span> <span class="o">(</span><span class="n">h''</span> <span class="o">:</span> <span class="n">d</span> <span class="bp">=</span> <span class="mi">2</span><span class="o">)</span> <span class="o">:</span> <span class="n">d</span> <span class="bp">+</span> <span class="n">a</span> <span class="bp">≤</span> <span class="mi">5</span> <span class="bp">*</span> <span class="n">b</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">linarith</span> </pre></div> </div> <p>In addition to equations and inequalities in the context,
-
@@ -815,40 +811,40 @@ applying a fact or theorem <code class="docutils literal notranslate"><span clasParentheses are only needed for compound arguments, as in <code class="docutils literal notranslate"><span class="pre">f</span> <span class="pre">(x</span> <span class="pre">+</span> <span class="pre">y)</span></code>. Without the parentheses, <code class="docutils literal notranslate"><span class="pre">f</span> <span class="pre">x</span> <span class="pre">+</span> <span class="pre">y</span></code> would be parsed as <code class="docutils literal notranslate"><span class="pre">(f</span> <span class="pre">x)</span> <span class="pre">+</span> <span class="pre">y</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">c</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">exp</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">exp</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">linarith</span><span class="w"> </span><span class="o">[</span><span class="n">exp_le_exp.mpr</span><span class="w"> </span><span class="n">h'</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="mi">1</span> <span class="bp">≤</span> <span class="n">a</span><span class="o">)</span> <span class="o">(</span><span class="n">h'</span> <span class="o">:</span> <span class="n">b</span> <span class="bp">≤</span> <span class="n">c</span><span class="o">)</span> <span class="o">:</span> <span class="mi">2</span> <span class="bp">+</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">exp</span> <span class="n">b</span> <span class="bp">≤</span> <span class="mi">3</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">exp</span> <span class="n">c</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">linarith</span> <span class="o">[</span><span class="n">exp_le_exp.mpr</span> <span class="n">h'</span><span class="o">]</span> </pre></div> </div> <p id="index-19">Here are some more theorems in the library that can be used to establish inequalities on the real numbers.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">exp_le_exp</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">exp</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">exp</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">exp_lt_exp</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">exp</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">exp</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">b</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">log_le_log</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">log</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">log</span><span class="w"> </span><span class="n">b</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">log_lt_log</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">log</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">log</span><span class="w"> </span><span class="n">b</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">add_le_add</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">d</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">add_le_add_left</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">c</span><span class="o">,</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">add_le_add_right</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">c</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">c</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">add_lt_add_of_le_of_lt</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">d</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">add_lt_add_of_lt_of_le</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">d</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">add_lt_add_left</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">c</span><span class="o">,</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">add_lt_add_right</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">c</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">c</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">add_nonneg</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">add_pos</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">add_pos_of_pos_of_nonneg</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">exp_pos</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">exp</span><span class="w"> </span><span class="n">a</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="n">add_le_add_left</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="o">(</span><span class="n">exp_le_exp</span> <span class="o">:</span> <span class="n">exp</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">exp</span> <span class="n">b</span> <span class="bp">↔</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">b</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">exp_lt_exp</span> <span class="o">:</span> <span class="n">exp</span> <span class="n">a</span> <span class="bp"><</span> <span class="n">exp</span> <span class="n">b</span> <span class="bp">↔</span> <span class="n">a</span> <span class="bp"><</span> <span class="n">b</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">log_le_log</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp"><</span> <span class="n">a</span> <span class="bp">→</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">b</span> <span class="bp">→</span> <span class="n">log</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">log</span> <span class="n">b</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">log_lt_log</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp"><</span> <span class="n">a</span> <span class="bp">→</span> <span class="n">a</span> <span class="bp"><</span> <span class="n">b</span> <span class="bp">→</span> <span class="n">log</span> <span class="n">a</span> <span class="bp"><</span> <span class="n">log</span> <span class="n">b</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">add_le_add</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">b</span> <span class="bp">→</span> <span class="n">c</span> <span class="bp">≤</span> <span class="n">d</span> <span class="bp">→</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">c</span> <span class="bp">≤</span> <span class="n">b</span> <span class="bp">+</span> <span class="n">d</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">add_le_add_left</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">b</span> <span class="bp">→</span> <span class="bp">∀</span> <span class="n">c</span><span class="o">,</span> <span class="n">c</span> <span class="bp">+</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">c</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">add_le_add_right</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">b</span> <span class="bp">→</span> <span class="bp">∀</span> <span class="n">c</span><span class="o">,</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">c</span> <span class="bp">≤</span> <span class="n">b</span> <span class="bp">+</span> <span class="n">c</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">add_lt_add_of_le_of_lt</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">b</span> <span class="bp">→</span> <span class="n">c</span> <span class="bp"><</span> <span class="n">d</span> <span class="bp">→</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">c</span> <span class="bp"><</span> <span class="n">b</span> <span class="bp">+</span> <span class="n">d</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">add_lt_add_of_lt_of_le</span> <span class="o">:</span> <span class="n">a</span> <span class="bp"><</span> <span class="n">b</span> <span class="bp">→</span> <span class="n">c</span> <span class="bp">≤</span> <span class="n">d</span> <span class="bp">→</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">c</span> <span class="bp"><</span> <span class="n">b</span> <span class="bp">+</span> <span class="n">d</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">add_lt_add_left</span> <span class="o">:</span> <span class="n">a</span> <span class="bp"><</span> <span class="n">b</span> <span class="bp">→</span> <span class="bp">∀</span> <span class="n">c</span><span class="o">,</span> <span class="n">c</span> <span class="bp">+</span> <span class="n">a</span> <span class="bp"><</span> <span class="n">c</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">add_lt_add_right</span> <span class="o">:</span> <span class="n">a</span> <span class="bp"><</span> <span class="n">b</span> <span class="bp">→</span> <span class="bp">∀</span> <span class="n">c</span><span class="o">,</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">c</span> <span class="bp"><</span> <span class="n">b</span> <span class="bp">+</span> <span class="n">c</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">add_nonneg</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp">≤</span> <span class="n">a</span> <span class="bp">→</span> <span class="mi">0</span> <span class="bp">≤</span> <span class="n">b</span> <span class="bp">→</span> <span class="mi">0</span> <span class="bp">≤</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">add_pos</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp"><</span> <span class="n">a</span> <span class="bp">→</span> <span class="mi">0</span> <span class="bp"><</span> <span class="n">b</span> <span class="bp">→</span> <span class="mi">0</span> <span class="bp"><</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">add_pos_of_pos_of_nonneg</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp"><</span> <span class="n">a</span> <span class="bp">→</span> <span class="mi">0</span> <span class="bp">≤</span> <span class="n">b</span> <span class="bp">→</span> <span class="mi">0</span> <span class="bp"><</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">exp_pos</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span><span class="o">,</span> <span class="mi">0</span> <span class="bp"><</span> <span class="n">exp</span> <span class="n">a</span><span class="o">)</span> <span class="k">#check</span> <span class="n">add_le_add_left</span> </pre></div> </div> <p>Some of the theorems, <code class="docutils literal notranslate"><span class="pre">exp_le_exp</span></code>, <code class="docutils literal notranslate"><span class="pre">exp_lt_exp</span></code> use a <em>bi-implication</em>, which represents the phrase “if and only if.” (You can type it in VS Code with <code class="docutils literal notranslate"><span class="pre">\lr</span></code> of <code class="docutils literal notranslate"><span class="pre">\iff</span></code>). (You can type it in VS Code with <code class="docutils literal notranslate"><span class="pre">\lr</span></code> or <code class="docutils literal notranslate"><span class="pre">\iff</span></code>). We will discuss this connective in greater detail in the next chapter. Such a theorem can be used with <code class="docutils literal notranslate"><span class="pre">rw</span></code> to rewrite a goal to an equivalent one:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">exp</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">exp</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">exp_le_exp</span><span class="o">]</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">h</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">b</span><span class="o">)</span> <span class="o">:</span> <span class="n">exp</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">exp</span> <span class="n">b</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">exp_le_exp</span><span class="o">]</span> <span class="n">exact</span> <span class="n">h</span> </pre></div> </div> <p>In this section, however, we will use the fact that if <code class="docutils literal notranslate"><span class="pre">h</span> <span class="pre">:</span> <span class="pre">A</span> <span class="pre">↔</span> <span class="pre">B</span></code>
-
@@ -860,11 +856,11 @@ Here, <code class="docutils literal notranslate"><span class="pre">mp</span></coYou can also use <code class="docutils literal notranslate"><span class="pre">h.1</span></code> and <code class="docutils literal notranslate"><span class="pre">h.2</span></code> for <code class="docutils literal notranslate"><span class="pre">h.mp</span></code> and <code class="docutils literal notranslate"><span class="pre">h.mpr</span></code>, respectively, if you prefer. Thus the following proof works:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h₀</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h₁</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">d</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">exp</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">e</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">exp</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">e</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">add_lt_add_of_lt_of_le</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">add_lt_add_of_le_of_lt</span><span class="w"> </span><span class="n">h₀</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">exp_lt_exp.mpr</span><span class="w"> </span><span class="n">h₁</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">le_refl</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">h₀</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">b</span><span class="o">)</span> <span class="o">(</span><span class="n">h₁</span> <span class="o">:</span> <span class="n">c</span> <span class="bp"><</span> <span class="n">d</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">exp</span> <span class="n">c</span> <span class="bp">+</span> <span class="n">e</span> <span class="bp"><</span> <span class="n">b</span> <span class="bp">+</span> <span class="n">exp</span> <span class="n">d</span> <span class="bp">+</span> <span class="n">e</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">apply</span> <span class="n">add_lt_add_of_lt_of_le</span> <span class="bp">·</span> <span class="n">apply</span> <span class="n">add_lt_add_of_le_of_lt</span> <span class="n">h₀</span> <span class="n">apply</span> <span class="n">exp_lt_exp.mpr</span> <span class="n">h₁</span> <span class="n">apply</span> <span class="n">le_refl</span> </pre></div> </div> <p>The first line, <code class="docutils literal notranslate"><span class="pre">apply</span> <span class="pre">add_lt_add_of_lt_of_le</span></code>,
-
@@ -874,14 +870,14 @@ proof of the first from the proof of the second.</p><p id="index-20">Try the following examples on your own. The example in the middle shows you that the <code class="docutils literal notranslate"><span class="pre">norm_num</span></code> tactic can be used to solve concrete numeric goals.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h₀</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">e</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">exp</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">d</span><span class="o">)</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">exp</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">e</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">h₀</span> <span class="o">:</span> <span class="n">d</span> <span class="bp">≤</span> <span class="n">e</span><span class="o">)</span> <span class="o">:</span> <span class="n">c</span> <span class="bp">+</span> <span class="n">exp</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">d</span><span class="o">)</span> <span class="bp">≤</span> <span class="n">c</span> <span class="bp">+</span> <span class="n">exp</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">e</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="mi">0</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">norm_num</span> <span class="kd">example</span> <span class="o">:</span> <span class="o">(</span><span class="mi">0</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="bp"><</span> <span class="mi">1</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">norm_num</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">log</span><span class="w"> </span><span class="o">(</span><span class="mi">1</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">exp</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">log</span><span class="w"> </span><span class="o">(</span><span class="mi">1</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">exp</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">h₀</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">exp</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">log_le_log</span><span class="w"> </span><span class="n">h₀</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">b</span><span class="o">)</span> <span class="o">:</span> <span class="n">log</span> <span class="o">(</span><span class="mi">1</span> <span class="bp">+</span> <span class="n">exp</span> <span class="n">a</span><span class="o">)</span> <span class="bp">≤</span> <span class="n">log</span> <span class="o">(</span><span class="mi">1</span> <span class="bp">+</span> <span class="n">exp</span> <span class="n">b</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="k">have</span> <span class="n">h₀</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp"><</span> <span class="mi">1</span> <span class="bp">+</span> <span class="n">exp</span> <span class="n">a</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="n">apply</span> <span class="n">log_le_log</span> <span class="n">h₀</span> <span class="gr">sorry</span> </pre></div> </div> <p>From these examples, it should be clear that being able to
-
@@ -911,9 +907,9 @@ and you can find similar theorems nearby.</p></li><li><p>You can use the <code class="docutils literal notranslate"><span class="pre">apply?</span></code> tactic, which tries to find the relevant theorem in the library.</p></li> </ul> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="c1">-- apply?</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">sq_nonneg</span><span class="w"> </span><span class="n">a</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp">≤</span> <span class="n">a</span> <span class="bp">^</span> <span class="mi">2</span> <span class="o">:=</span> <span class="kd">by</span> <span class="c1">-- apply?</span> <span class="n">exact</span> <span class="n">sq_nonneg</span> <span class="n">a</span> </pre></div> </div> <p>To try out <code class="docutils literal notranslate"><span class="pre">apply?</span></code> in this example,
-
@@ -921,23 +917,23 @@ delete the <code class="docutils literal notranslate"><span class="pre">exact</sUsing these tricks, see if you can find what you need to do the next example:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">exp</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">exp</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">b</span><span class="o">)</span> <span class="o">:</span> <span class="n">c</span> <span class="bp">-</span> <span class="n">exp</span> <span class="n">b</span> <span class="bp">≤</span> <span class="n">c</span> <span class="bp">-</span> <span class="n">exp</span> <span class="n">a</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>Using the same tricks, confirm that <code class="docutils literal notranslate"><span class="pre">linarith</span></code> instead of <code class="docutils literal notranslate"><span class="pre">apply?</span></code> can also finish the job.</p> <p>Here is another example of an inequality:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="bp">*</span><span class="n">a</span><span class="bp">*</span><span class="n">b</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">a</span><span class="bp">^</span><span class="mi">2</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="bp">^</span><span class="mi">2</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">a</span><span class="bp">^</span><span class="mi">2</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="mi">2</span><span class="bp">*</span><span class="n">a</span><span class="bp">*</span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="bp">^</span><span class="mi">2</span> <span class="w"> </span><span class="k">calc</span> <span class="w"> </span><span class="n">a</span><span class="bp">^</span><span class="mi">2</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="mi">2</span><span class="bp">*</span><span class="n">a</span><span class="bp">*</span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="bp">^</span><span class="mi">2</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="bp">^</span><span class="mi">2</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">ring</span> <span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">≥</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">pow_two_nonneg</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="mi">2</span><span class="bp">*</span><span class="n">a</span><span class="bp">*</span><span class="n">b</span> <span class="bp">≤</span> <span class="n">a</span><span class="bp">^</span><span class="mi">2</span> <span class="bp">+</span> <span class="n">b</span><span class="bp">^</span><span class="mi">2</span> <span class="o">:=</span> <span class="kd">by</span> <span class="k">have</span> <span class="n">h</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp">≤</span> <span class="n">a</span><span class="bp">^</span><span class="mi">2</span> <span class="bp">-</span> <span class="mi">2</span><span class="bp">*</span><span class="n">a</span><span class="bp">*</span><span class="n">b</span> <span class="bp">+</span> <span class="n">b</span><span class="bp">^</span><span class="mi">2</span> <span class="k">calc</span> <span class="n">a</span><span class="bp">^</span><span class="mi">2</span> <span class="bp">-</span> <span class="mi">2</span><span class="bp">*</span><span class="n">a</span><span class="bp">*</span><span class="n">b</span> <span class="bp">+</span> <span class="n">b</span><span class="bp">^</span><span class="mi">2</span> <span class="bp">=</span> <span class="o">(</span><span class="n">a</span> <span class="bp">-</span> <span class="n">b</span><span class="o">)</span><span class="bp">^</span><span class="mi">2</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">ring</span> <span class="n">_</span> <span class="bp">≥</span> <span class="mi">0</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">apply</span> <span class="n">pow_two_nonneg</span> <span class="w"> </span><span class="k">calc</span> <span class="w"> </span><span class="mi">2</span><span class="bp">*</span><span class="n">a</span><span class="bp">*</span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">2</span><span class="bp">*</span><span class="n">a</span><span class="bp">*</span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">ring</span> <span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="mi">2</span><span class="bp">*</span><span class="n">a</span><span class="bp">*</span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="bp">^</span><span class="mi">2</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="mi">2</span><span class="bp">*</span><span class="n">a</span><span class="bp">*</span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="bp">^</span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">add_le_add</span><span class="w"> </span><span class="o">(</span><span class="n">le_refl</span><span class="w"> </span><span class="n">_</span><span class="o">)</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="bp">^</span><span class="mi">2</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="bp">^</span><span class="mi">2</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">ring</span> <span class="k">calc</span> <span class="mi">2</span><span class="bp">*</span><span class="n">a</span><span class="bp">*</span><span class="n">b</span> <span class="bp">=</span> <span class="mi">2</span><span class="bp">*</span><span class="n">a</span><span class="bp">*</span><span class="n">b</span> <span class="bp">+</span> <span class="mi">0</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">ring</span> <span class="n">_</span> <span class="bp">≤</span> <span class="mi">2</span><span class="bp">*</span><span class="n">a</span><span class="bp">*</span><span class="n">b</span> <span class="bp">+</span> <span class="o">(</span><span class="n">a</span><span class="bp">^</span><span class="mi">2</span> <span class="bp">-</span> <span class="mi">2</span><span class="bp">*</span><span class="n">a</span><span class="bp">*</span><span class="n">b</span> <span class="bp">+</span> <span class="n">b</span><span class="bp">^</span><span class="mi">2</span><span class="o">)</span> <span class="o">:=</span> <span class="n">add_le_add</span> <span class="o">(</span><span class="n">le_refl</span> <span class="n">_</span><span class="o">)</span> <span class="n">h</span> <span class="n">_</span> <span class="bp">=</span> <span class="n">a</span><span class="bp">^</span><span class="mi">2</span> <span class="bp">+</span> <span class="n">b</span><span class="bp">^</span><span class="mi">2</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">ring</span> </pre></div> </div> <p>Mathlib tends to put spaces around binary operations like <code class="docutils literal notranslate"><span class="pre">*</span></code> and <code class="docutils literal notranslate"><span class="pre">^</span></code>,
-
@@ -957,34 +953,34 @@ we can simply write the proof term <code class="docutils literal notranslate"><sout the hypothesis <code class="docutils literal notranslate"><span class="pre">h</span></code>. Once we have it, the second calculation involves only linear arithmetic, and <code class="docutils literal notranslate"><span class="pre">linarith</span></code> can handle it:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="bp">*</span><span class="n">a</span><span class="bp">*</span><span class="n">b</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">a</span><span class="bp">^</span><span class="mi">2</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="bp">^</span><span class="mi">2</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">a</span><span class="bp">^</span><span class="mi">2</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="mi">2</span><span class="bp">*</span><span class="n">a</span><span class="bp">*</span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="bp">^</span><span class="mi">2</span> <span class="w"> </span><span class="k">calc</span> <span class="w"> </span><span class="n">a</span><span class="bp">^</span><span class="mi">2</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="mi">2</span><span class="bp">*</span><span class="n">a</span><span class="bp">*</span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="bp">^</span><span class="mi">2</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="bp">^</span><span class="mi">2</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">ring</span> <span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">≥</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">pow_two_nonneg</span> <span class="w"> </span><span class="n">linarith</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="mi">2</span><span class="bp">*</span><span class="n">a</span><span class="bp">*</span><span class="n">b</span> <span class="bp">≤</span> <span class="n">a</span><span class="bp">^</span><span class="mi">2</span> <span class="bp">+</span> <span class="n">b</span><span class="bp">^</span><span class="mi">2</span> <span class="o">:=</span> <span class="kd">by</span> <span class="k">have</span> <span class="n">h</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp">≤</span> <span class="n">a</span><span class="bp">^</span><span class="mi">2</span> <span class="bp">-</span> <span class="mi">2</span><span class="bp">*</span><span class="n">a</span><span class="bp">*</span><span class="n">b</span> <span class="bp">+</span> <span class="n">b</span><span class="bp">^</span><span class="mi">2</span> <span class="k">calc</span> <span class="n">a</span><span class="bp">^</span><span class="mi">2</span> <span class="bp">-</span> <span class="mi">2</span><span class="bp">*</span><span class="n">a</span><span class="bp">*</span><span class="n">b</span> <span class="bp">+</span> <span class="n">b</span><span class="bp">^</span><span class="mi">2</span> <span class="bp">=</span> <span class="o">(</span><span class="n">a</span> <span class="bp">-</span> <span class="n">b</span><span class="o">)</span><span class="bp">^</span><span class="mi">2</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">ring</span> <span class="n">_</span> <span class="bp">≥</span> <span class="mi">0</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">apply</span> <span class="n">pow_two_nonneg</span> <span class="n">linarith</span> </pre></div> </div> <p>How nice! We challenge you to use these ideas to prove the following theorem. You can use the theorem <code class="docutils literal notranslate"><span class="pre">abs_le'.mpr</span></code>. You will also need the <code class="docutils literal notranslate"><span class="pre">constructor</span></code> tactic to split a conjunction to two goals; see <a class="reference internal" href="C03_Logic.html#conjunction-and-biimplication"><span class="std std-numref">Section 3.4</span></a>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">|</span><span class="n">a</span><span class="bp">*</span><span class="n">b</span><span class="bp">|</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="bp">^</span><span class="mi">2</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="bp">^</span><span class="mi">2</span><span class="o">)</span><span class="bp">/</span><span class="mi">2</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="bp">|</span><span class="n">a</span><span class="bp">*</span><span class="n">b</span><span class="bp">|</span> <span class="bp">≤</span> <span class="o">(</span><span class="n">a</span><span class="bp">^</span><span class="mi">2</span> <span class="bp">+</span> <span class="n">b</span><span class="bp">^</span><span class="mi">2</span><span class="o">)</span><span class="bp">/</span><span class="mi">2</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="k">#check</span><span class="w"> </span><span class="n">abs_le'.mpr</span> <span class="k">#check</span> <span class="n">abs_le'.mpr</span> </pre></div> </div> <p>If you managed to solve this, congratulations! You are well on your way to becoming a master formalizer.</p> </section> <section id="more-examples-using-apply-and-rw"> <span id="more-on-order-and-divisibility"></span><h2><span class="section-number">2.4. </span>More examples using apply and rw<a class="headerlink" href="#more-examples-using-apply-and-rw" title="Link to this heading"></a></h2> <span id="more-on-order-and-divisibility"></span><h2><span class="section-number">2.4. </span>More examples using apply and rw<a class="headerlink" href="#more-examples-using-apply-and-rw" title="Permalink to this heading"></a></h2> <p id="index-21">The <code class="docutils literal notranslate"><span class="pre">min</span></code> function on the real numbers is uniquely characterized by the following three facts:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">min_le_left</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">min</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">a</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">min_le_right</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">min</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">le_min</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">min</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="o">(</span><span class="n">min_le_left</span> <span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">min</span> <span class="n">a</span> <span class="n">b</span> <span class="bp">≤</span> <span class="n">a</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">min_le_right</span> <span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">min</span> <span class="n">a</span> <span class="n">b</span> <span class="bp">≤</span> <span class="n">b</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">le_min</span> <span class="o">:</span> <span class="n">c</span> <span class="bp">≤</span> <span class="n">a</span> <span class="bp">→</span> <span class="n">c</span> <span class="bp">≤</span> <span class="n">b</span> <span class="bp">→</span> <span class="n">c</span> <span class="bp">≤</span> <span class="n">min</span> <span class="n">a</span> <span class="n">b</span><span class="o">)</span> </pre></div> </div> <p>Can you guess the names of the theorems that characterize
-
@@ -1009,16 +1005,16 @@ With time, these conventions will become second nature.</p>real numbers are equal if each is less than or equal to the other. Using this and the facts above, we can show that <code class="docutils literal notranslate"><span class="pre">min</span></code> is commutative:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">min</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">min</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">le_antisymm</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="k">show</span><span class="w"> </span><span class="n">min</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">min</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">a</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">le_min</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">min_le_right</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">min_le_left</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="k">show</span><span class="w"> </span><span class="n">min</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">min</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">le_min</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">min_le_right</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">min_le_left</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">min</span> <span class="n">a</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">min</span> <span class="n">b</span> <span class="n">a</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">apply</span> <span class="n">le_antisymm</span> <span class="bp">·</span> <span class="k">show</span> <span class="n">min</span> <span class="n">a</span> <span class="n">b</span> <span class="bp">≤</span> <span class="n">min</span> <span class="n">b</span> <span class="n">a</span> <span class="n">apply</span> <span class="n">le_min</span> <span class="bp">·</span> <span class="n">apply</span> <span class="n">min_le_right</span> <span class="n">apply</span> <span class="n">min_le_left</span> <span class="bp">·</span> <span class="k">show</span> <span class="n">min</span> <span class="n">b</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">min</span> <span class="n">a</span> <span class="n">b</span> <span class="n">apply</span> <span class="n">le_min</span> <span class="bp">·</span> <span class="n">apply</span> <span class="n">min_le_right</span> <span class="n">apply</span> <span class="n">min_le_left</span> </pre></div> </div> <p id="index-22">Here we have used dots to separate proofs of
-
@@ -1038,15 +1034,15 @@ but using them makes the proof easier to read and maintain.</p>To foreshadow skills you will learn later on, we note that one way to avoid the repetition is to state a local lemma and then use it:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">min</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">min</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">,</span><span class="w"> </span><span class="n">min</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">min</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">le_min</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">min_le_right</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">min_le_left</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">le_antisymm</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">h</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">min</span> <span class="n">a</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">min</span> <span class="n">b</span> <span class="n">a</span> <span class="o">:=</span> <span class="kd">by</span> <span class="k">have</span> <span class="n">h</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">,</span> <span class="n">min</span> <span class="n">x</span> <span class="n">y</span> <span class="bp">≤</span> <span class="n">min</span> <span class="n">y</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">x</span> <span class="n">y</span> <span class="n">apply</span> <span class="n">le_min</span> <span class="n">apply</span> <span class="n">min_le_right</span> <span class="n">apply</span> <span class="n">min_le_left</span> <span class="n">apply</span> <span class="n">le_antisymm</span> <span class="n">apply</span> <span class="n">h</span> <span class="n">apply</span> <span class="n">h</span> </pre></div> </div> <p>We will say more about the universal quantifier in
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@@ -1061,20 +1057,20 @@ uses <code class="docutils literal notranslate"><span class="pre">h</span> <span<p id="index-23">Another solution is to use the <code class="docutils literal notranslate"><span class="pre">repeat</span></code> tactic, which applies a tactic (or a block) as many times as it can.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">min</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">min</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">le_antisymm</span> <span class="w"> </span><span class="n">repeat</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">le_min</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">min_le_right</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">min_le_left</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">min</span> <span class="n">a</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">min</span> <span class="n">b</span> <span class="n">a</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">apply</span> <span class="n">le_antisymm</span> <span class="n">repeat</span> <span class="n">apply</span> <span class="n">le_min</span> <span class="n">apply</span> <span class="n">min_le_right</span> <span class="n">apply</span> <span class="n">min_le_left</span> </pre></div> </div> <p>We encourage you to prove the following as exercises. You can use either of the tricks just described to shorten the first.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">max</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">max</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">min</span><span class="w"> </span><span class="o">(</span><span class="n">min</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">min</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">(</span><span class="n">min</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">max</span> <span class="n">a</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">max</span> <span class="n">b</span> <span class="n">a</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">min</span> <span class="o">(</span><span class="n">min</span> <span class="n">a</span> <span class="n">b</span><span class="o">)</span> <span class="n">c</span> <span class="bp">=</span> <span class="n">min</span> <span class="n">a</span> <span class="o">(</span><span class="n">min</span> <span class="n">b</span> <span class="n">c</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>Of course, you are welcome to prove the associativity of <code class="docutils literal notranslate"><span class="pre">max</span></code> as well.</p>
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@@ -1097,10 +1093,10 @@ and in the second case, we have <code class="docutils literal notranslate"><spanWe will learn how to reason by cases in <a class="reference internal" href="C03_Logic.html#disjunction"><span class="std std-numref">Section 3.5</span></a>, but for now we will stick to examples that don’t require the case split.</p> <p>Here is one such example:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">aux</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">min</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">min</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">c</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">c</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">min</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">min</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">c</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">c</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">aux</span> <span class="o">:</span> <span class="n">min</span> <span class="n">a</span> <span class="n">b</span> <span class="bp">+</span> <span class="n">c</span> <span class="bp">≤</span> <span class="n">min</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">c</span><span class="o">)</span> <span class="o">(</span><span class="n">b</span> <span class="bp">+</span> <span class="n">c</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">min</span> <span class="n">a</span> <span class="n">b</span> <span class="bp">+</span> <span class="n">c</span> <span class="bp">=</span> <span class="n">min</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">c</span><span class="o">)</span> <span class="o">(</span><span class="n">b</span> <span class="bp">+</span> <span class="n">c</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>It is clear that <code class="docutils literal notranslate"><span class="pre">aux</span></code> provides one of the two inequalities
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@@ -1111,12 +1107,12 @@ As a hint, you can use the theorem <code class="docutils literal notranslate"><sand the <code class="docutils literal notranslate"><span class="pre">linarith</span></code> tactic.</p> <p id="index-24">Lean’s naming convention is made manifest in the library’s name for the triangle inequality:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">abs_add</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">,</span><span class="w"> </span><span class="bp">|</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="bp">|</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="bp">|</span><span class="n">a</span><span class="bp">|</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="bp">|</span><span class="n">b</span><span class="bp">|</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="o">(</span><span class="n">abs_add</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">,</span> <span class="bp">|</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="bp">|</span> <span class="bp">≤</span> <span class="bp">|</span><span class="n">a</span><span class="bp">|</span> <span class="bp">+</span> <span class="bp">|</span><span class="n">b</span><span class="bp">|</span><span class="o">)</span> </pre></div> </div> <p>Use it to prove the following variant, using also <code class="docutils literal notranslate"><span class="pre">add_sub_cancel_right</span></code>:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">|</span><span class="n">a</span><span class="bp">|</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="bp">|</span><span class="n">b</span><span class="bp">|</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="bp">|</span><span class="n">a</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">b</span><span class="bp">|</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="bp">|</span><span class="n">a</span><span class="bp">|</span> <span class="bp">-</span> <span class="bp">|</span><span class="n">b</span><span class="bp">|</span> <span class="bp">≤</span> <span class="bp">|</span><span class="n">a</span> <span class="bp">-</span> <span class="n">b</span><span class="bp">|</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="kd">end</span> </pre></div> </div>
-
@@ -1131,15 +1127,15 @@ Rather, it is a unicode character obtained bytyping <code class="docutils literal notranslate"><span class="pre">\|</span></code> in VS Code. By convention, Mathlib uses <code class="docutils literal notranslate"><span class="pre">dvd</span></code> to refer to it in theorem names.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h₀</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h₁</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">z</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">dvd_trans</span><span class="w"> </span><span class="n">h₀</span><span class="w"> </span><span class="n">h₁</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">h₀</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">∣</span> <span class="n">y</span><span class="o">)</span> <span class="o">(</span><span class="n">h₁</span> <span class="o">:</span> <span class="n">y</span> <span class="bp">∣</span> <span class="n">z</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">∣</span> <span class="n">z</span> <span class="o">:=</span> <span class="n">dvd_trans</span> <span class="n">h₀</span> <span class="n">h₁</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">dvd_mul_of_dvd_left</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">dvd_mul_left</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">∣</span> <span class="n">y</span> <span class="bp">*</span> <span class="n">x</span> <span class="bp">*</span> <span class="n">z</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">apply</span> <span class="n">dvd_mul_of_dvd_left</span> <span class="n">apply</span> <span class="n">dvd_mul_left</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">dvd_mul_left</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">∣</span> <span class="n">x</span> <span class="bp">^</span> <span class="mi">2</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">apply</span> <span class="n">dvd_mul_left</span> </pre></div> </div> <p>In the last example, the exponent is a natural
-
@@ -1148,8 +1144,8 @@ forces Lean to expand the definition of <code class="docutils literal notranslat<code class="docutils literal notranslate"><span class="pre">x^1</span> <span class="pre">*</span> <span class="pre">x</span></code>. See if you can guess the names of the theorems you need to prove the following:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">w</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">z</span><span class="o">)</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">w</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">∣</span> <span class="n">w</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">∣</span> <span class="n">y</span> <span class="bp">*</span> <span class="o">(</span><span class="n">x</span> <span class="bp">*</span> <span class="n">z</span><span class="o">)</span> <span class="bp">+</span> <span class="n">x</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">+</span> <span class="n">w</span> <span class="bp">^</span> <span class="mi">2</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">end</span> </pre></div> </div>
-
@@ -1158,18 +1154,18 @@ you need to prove the following:</p>are analogous to <code class="docutils literal notranslate"><span class="pre">min</span></code> and <code class="docutils literal notranslate"><span class="pre">max</span></code>. Since every number divides <code class="docutils literal notranslate"><span class="pre">0</span></code>, <code class="docutils literal notranslate"><span class="pre">0</span></code> is really the greatest element with respect to divisibility:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">(</span><span class="n">m</span> <span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">Nat.gcd_zero_right</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat.gcd</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">n</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">Nat.gcd_zero_left</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat.gcd</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">n</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">Nat.lcm_zero_right</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat.lcm</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">Nat.lcm_zero_left</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat.lcm</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">Nat.gcd_zero_right</span> <span class="n">n</span> <span class="o">:</span> <span class="n">Nat.gcd</span> <span class="n">n</span> <span class="mi">0</span> <span class="bp">=</span> <span class="n">n</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">Nat.gcd_zero_left</span> <span class="n">n</span> <span class="o">:</span> <span class="n">Nat.gcd</span> <span class="mi">0</span> <span class="n">n</span> <span class="bp">=</span> <span class="n">n</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">Nat.lcm_zero_right</span> <span class="n">n</span> <span class="o">:</span> <span class="n">Nat.lcm</span> <span class="n">n</span> <span class="mi">0</span> <span class="bp">=</span> <span class="mi">0</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">Nat.lcm_zero_left</span> <span class="n">n</span> <span class="o">:</span> <span class="n">Nat.lcm</span> <span class="mi">0</span> <span class="n">n</span> <span class="bp">=</span> <span class="mi">0</span><span class="o">)</span> </pre></div> </div> <p>See if you can guess the names of the theorems you will need to prove the following:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat.gcd</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">Nat.gcd</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">Nat.gcd</span> <span class="n">m</span> <span class="n">n</span> <span class="bp">=</span> <span class="n">Nat.gcd</span> <span class="n">n</span> <span class="n">m</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>Hint: you can use <code class="docutils literal notranslate"><span class="pre">dvd_antisymm</span></code>, but if you do, Lean will
-
@@ -1180,7 +1176,7 @@ You can use <code class="docutils literal notranslate"><span class="pre">_root_.either one will work.</p> </section> <section id="proving-facts-about-algebraic-structures"> <span id="id4"></span><h2><span class="section-number">2.5. </span>Proving Facts about Algebraic Structures<a class="headerlink" href="#proving-facts-about-algebraic-structures" title="Link to this heading"></a></h2> <span id="id4"></span><h2><span class="section-number">2.5. </span>Proving Facts about Algebraic Structures<a class="headerlink" href="#proving-facts-about-algebraic-structures" title="Permalink to this heading"></a></h2> <p id="index-27">In <a class="reference internal" href="#proving-identities-in-algebraic-structures"><span class="std std-numref">Section 2.2</span></a>, we saw that many common identities governing the real numbers hold in more general classes of algebraic structures,
-
@@ -1191,13 +1187,13 @@ For example, a <em>partial order</em> consists of a set with abinary relation that is reflexive, transitive, and antisymmetric. like <code class="docutils literal notranslate"><span class="pre">≤</span></code> on the real numbers. Lean knows about partial orders:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">PartialOrder</span><span class="w"> </span><span class="n">α</span><span class="o">]</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">PartialOrder</span> <span class="n">α</span><span class="o">]</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="n">z</span> <span class="o">:</span> <span class="n">α</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">le_refl</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">x</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">le_trans</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">z</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">le_antisymm</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">y</span><span class="o">)</span> <span class="k">#check</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">y</span> <span class="k">#check</span> <span class="o">(</span><span class="n">le_refl</span> <span class="n">x</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">x</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">le_trans</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">y</span> <span class="bp">→</span> <span class="n">y</span> <span class="bp">≤</span> <span class="n">z</span> <span class="bp">→</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">z</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">le_antisymm</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">y</span> <span class="bp">→</span> <span class="n">y</span> <span class="bp">≤</span> <span class="n">x</span> <span class="bp">→</span> <span class="n">x</span> <span class="bp">=</span> <span class="n">y</span><span class="o">)</span> </pre></div> </div> <p>Here we are adopting the Mathlib convention of using
-
@@ -1216,14 +1212,14 @@ which acts somewhat like <code class="docutils literal notranslate"><span class=Saying that <code class="docutils literal notranslate"><span class="pre">x</span></code> is less than <code class="docutils literal notranslate"><span class="pre">y</span></code> in this order is equivalent to saying that it is less-than-or-equal to <code class="docutils literal notranslate"><span class="pre">y</span></code> and not equal to <code class="docutils literal notranslate"><span class="pre">y</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">y</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">lt_irrefl</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">x</span><span class="o">))</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">lt_trans</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">z</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">lt_of_le_of_lt</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">z</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">lt_of_lt_of_le</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">z</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="n">x</span> <span class="bp"><</span> <span class="n">y</span> <span class="k">#check</span> <span class="o">(</span><span class="n">lt_irrefl</span> <span class="n">x</span> <span class="o">:</span> <span class="bp">¬</span> <span class="o">(</span><span class="n">x</span> <span class="bp"><</span> <span class="n">x</span><span class="o">))</span> <span class="k">#check</span> <span class="o">(</span><span class="n">lt_trans</span> <span class="o">:</span> <span class="n">x</span> <span class="bp"><</span> <span class="n">y</span> <span class="bp">→</span> <span class="n">y</span> <span class="bp"><</span> <span class="n">z</span> <span class="bp">→</span> <span class="n">x</span> <span class="bp"><</span> <span class="n">z</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">lt_of_le_of_lt</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">y</span> <span class="bp">→</span> <span class="n">y</span> <span class="bp"><</span> <span class="n">z</span> <span class="bp">→</span> <span class="n">x</span> <span class="bp"><</span> <span class="n">z</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">lt_of_lt_of_le</span> <span class="o">:</span> <span class="n">x</span> <span class="bp"><</span> <span class="n">y</span> <span class="bp">→</span> <span class="n">y</span> <span class="bp">≤</span> <span class="n">z</span> <span class="bp">→</span> <span class="n">x</span> <span class="bp"><</span> <span class="n">z</span><span class="o">)</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">lt_iff_le_and_ne</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">x</span> <span class="bp"><</span> <span class="n">y</span> <span class="bp">↔</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">y</span> <span class="bp">∧</span> <span class="n">x</span> <span class="bp">≠</span> <span class="n">y</span> <span class="o">:=</span> <span class="n">lt_iff_le_and_ne</span> </pre></div> </div> <p>In this example, the symbol <code class="docutils literal notranslate"><span class="pre">∧</span></code> stands for “and,”
-
@@ -1235,17 +1231,17 @@ has the properties indicated.</p><p id="index-28">A <em>lattice</em> is a structure that extends a partial order with operations <code class="docutils literal notranslate"><span class="pre">⊓</span></code> and <code class="docutils literal notranslate"><span class="pre">⊔</span></code> that are analogous to <code class="docutils literal notranslate"><span class="pre">min</span></code> and <code class="docutils literal notranslate"><span class="pre">max</span></code> on the real numbers:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Lattice</span><span class="w"> </span><span class="n">α</span><span class="o">]</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Lattice</span> <span class="n">α</span><span class="o">]</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="n">z</span> <span class="o">:</span> <span class="n">α</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">y</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">inf_le_left</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">x</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">inf_le_right</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">le_inf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">y</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">y</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">le_sup_left</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">y</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">le_sup_right</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">y</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">sup_le</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">z</span><span class="o">)</span> <span class="k">#check</span> <span class="n">x</span> <span class="bp">⊓</span> <span class="n">y</span> <span class="k">#check</span> <span class="o">(</span><span class="n">inf_le_left</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">⊓</span> <span class="n">y</span> <span class="bp">≤</span> <span class="n">x</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">inf_le_right</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">⊓</span> <span class="n">y</span> <span class="bp">≤</span> <span class="n">y</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">le_inf</span> <span class="o">:</span> <span class="n">z</span> <span class="bp">≤</span> <span class="n">x</span> <span class="bp">→</span> <span class="n">z</span> <span class="bp">≤</span> <span class="n">y</span> <span class="bp">→</span> <span class="n">z</span> <span class="bp">≤</span> <span class="n">x</span> <span class="bp">⊓</span> <span class="n">y</span><span class="o">)</span> <span class="k">#check</span> <span class="n">x</span> <span class="bp">⊔</span> <span class="n">y</span> <span class="k">#check</span> <span class="o">(</span><span class="n">le_sup_left</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">x</span> <span class="bp">⊔</span> <span class="n">y</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">le_sup_right</span> <span class="o">:</span> <span class="n">y</span> <span class="bp">≤</span> <span class="n">x</span> <span class="bp">⊔</span> <span class="n">y</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">sup_le</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">z</span> <span class="bp">→</span> <span class="n">y</span> <span class="bp">≤</span> <span class="n">z</span> <span class="bp">→</span> <span class="n">x</span> <span class="bp">⊔</span> <span class="n">y</span> <span class="bp">≤</span> <span class="n">z</span><span class="o">)</span> </pre></div> </div> <p>The characterizations of <code class="docutils literal notranslate"><span class="pre">⊓</span></code> and <code class="docutils literal notranslate"><span class="pre">⊔</span></code> justify calling them
-
@@ -1300,28 +1296,28 @@ which takes <code class="docutils literal notranslate"><span class="pre">y</spanOf course you can also avoid this issue by providing directly a full proof such as <code class="docutils literal notranslate"><span class="pre">exact</span> <span class="pre">le_trans</span> <span class="pre">inf_le_left</span> <span class="pre">inf_le_right</span></code>, but this requires a lot more planning.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">⊓</span> <span class="n">y</span> <span class="bp">=</span> <span class="n">y</span> <span class="bp">⊓</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="o">(</span><span class="n">y</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">z</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">⊓</span> <span class="n">y</span> <span class="bp">⊓</span> <span class="n">z</span> <span class="bp">=</span> <span class="n">x</span> <span class="bp">⊓</span> <span class="o">(</span><span class="n">y</span> <span class="bp">⊓</span> <span class="n">z</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">⊔</span> <span class="n">y</span> <span class="bp">=</span> <span class="n">y</span> <span class="bp">⊔</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="o">(</span><span class="n">y</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">z</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">⊔</span> <span class="n">y</span> <span class="bp">⊔</span> <span class="n">z</span> <span class="bp">=</span> <span class="n">x</span> <span class="bp">⊔</span> <span class="o">(</span><span class="n">y</span> <span class="bp">⊔</span> <span class="n">z</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>You can find these theorems in the Mathlib as <code class="docutils literal notranslate"><span class="pre">inf_comm</span></code>, <code class="docutils literal notranslate"><span class="pre">inf_assoc</span></code>, <code class="docutils literal notranslate"><span class="pre">sup_comm</span></code>, and <code class="docutils literal notranslate"><span class="pre">sup_assoc</span></code>, respectively.</p> <p>Another good exercise is to prove the <em>absorption laws</em> using only those axioms:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">absorb1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">absorb1</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">⊓</span> <span class="o">(</span><span class="n">x</span> <span class="bp">⊔</span> <span class="n">y</span><span class="o">)</span> <span class="bp">=</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">absorb2</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">theorem</span> <span class="n">absorb2</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">⊔</span> <span class="n">x</span> <span class="bp">⊓</span> <span class="n">y</span> <span class="bp">=</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>These can be found in Mathlib with the names <code class="docutils literal notranslate"><span class="pre">inf_sup_self</span></code> and <code class="docutils literal notranslate"><span class="pre">sup_inf_self</span></code>.</p>
-
@@ -1329,13 +1325,13 @@ using only those axioms:</p><code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">⊓</span> <span class="pre">(y</span> <span class="pre">⊔</span> <span class="pre">z)</span> <span class="pre">=</span> <span class="pre">(x</span> <span class="pre">⊓</span> <span class="pre">y)</span> <span class="pre">⊔</span> <span class="pre">(x</span> <span class="pre">⊓</span> <span class="pre">z)</span></code> and <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">⊔</span> <span class="pre">(y</span> <span class="pre">⊓</span> <span class="pre">z)</span> <span class="pre">=</span> <span class="pre">(x</span> <span class="pre">⊔</span> <span class="pre">y)</span> <span class="pre">⊓</span> <span class="pre">(x</span> <span class="pre">⊔</span> <span class="pre">z)</span></code> is called a <em>distributive lattice</em>. Lean knows about these too:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">DistribLattice</span><span class="w"> </span><span class="n">α</span><span class="o">]</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">DistribLattice</span> <span class="n">α</span><span class="o">]</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="n">z</span> <span class="o">:</span> <span class="n">α</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">inf_sup_left</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="o">(</span><span class="n">y</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">z</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">z</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">inf_sup_right</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">z</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">sup_inf_left</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">z</span><span class="o">))</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">sup_inf_right</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">z</span><span class="o">)</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="o">(</span><span class="n">y</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">z</span><span class="o">))</span> <span class="k">#check</span> <span class="o">(</span><span class="n">inf_sup_left</span> <span class="n">x</span> <span class="n">y</span> <span class="n">z</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">⊓</span> <span class="o">(</span><span class="n">y</span> <span class="bp">⊔</span> <span class="n">z</span><span class="o">)</span> <span class="bp">=</span> <span class="n">x</span> <span class="bp">⊓</span> <span class="n">y</span> <span class="bp">⊔</span> <span class="n">x</span> <span class="bp">⊓</span> <span class="n">z</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">inf_sup_right</span> <span class="n">x</span> <span class="n">y</span> <span class="n">z</span> <span class="o">:</span> <span class="o">(</span><span class="n">x</span> <span class="bp">⊔</span> <span class="n">y</span><span class="o">)</span> <span class="bp">⊓</span> <span class="n">z</span> <span class="bp">=</span> <span class="n">x</span> <span class="bp">⊓</span> <span class="n">z</span> <span class="bp">⊔</span> <span class="n">y</span> <span class="bp">⊓</span> <span class="n">z</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">sup_inf_left</span> <span class="n">x</span> <span class="n">y</span> <span class="n">z</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">⊔</span> <span class="n">y</span> <span class="bp">⊓</span> <span class="n">z</span> <span class="bp">=</span> <span class="o">(</span><span class="n">x</span> <span class="bp">⊔</span> <span class="n">y</span><span class="o">)</span> <span class="bp">⊓</span> <span class="o">(</span><span class="n">x</span> <span class="bp">⊔</span> <span class="n">z</span><span class="o">))</span> <span class="k">#check</span> <span class="o">(</span><span class="n">sup_inf_right</span> <span class="n">x</span> <span class="n">y</span> <span class="n">z</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">⊓</span> <span class="n">y</span> <span class="bp">⊔</span> <span class="n">z</span> <span class="bp">=</span> <span class="o">(</span><span class="n">x</span> <span class="bp">⊔</span> <span class="n">z</span><span class="o">)</span> <span class="bp">⊓</span> <span class="o">(</span><span class="n">y</span> <span class="bp">⊔</span> <span class="n">z</span><span class="o">))</span> </pre></div> </div> <p>The left and right versions are easily shown to be
-
@@ -1346,14 +1342,14 @@ by providing an explicit description of anondistributive lattice with finitely many elements. It is also a good exercise to show that in any lattice, either distributivity law implies the other:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Lattice</span><span class="w"> </span><span class="n">α</span><span class="o">]</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Lattice</span> <span class="n">α</span><span class="o">]</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">α</span><span class="o">)</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">,</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="o">(</span><span class="n">y</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">z</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">z</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">c</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span> <span class="n">y</span> <span class="n">z</span> <span class="o">:</span> <span class="n">α</span><span class="o">,</span> <span class="n">x</span> <span class="bp">⊓</span> <span class="o">(</span><span class="n">y</span> <span class="bp">⊔</span> <span class="n">z</span><span class="o">)</span> <span class="bp">=</span> <span class="n">x</span> <span class="bp">⊓</span> <span class="n">y</span> <span class="bp">⊔</span> <span class="n">x</span> <span class="bp">⊓</span> <span class="n">z</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">⊔</span> <span class="n">b</span> <span class="bp">⊓</span> <span class="n">c</span> <span class="bp">=</span> <span class="o">(</span><span class="n">a</span> <span class="bp">⊔</span> <span class="n">b</span><span class="o">)</span> <span class="bp">⊓</span> <span class="o">(</span><span class="n">a</span> <span class="bp">⊔</span> <span class="n">c</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">,</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">z</span><span class="o">))</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="o">(</span><span class="n">b</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">c</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span> <span class="n">y</span> <span class="n">z</span> <span class="o">:</span> <span class="n">α</span><span class="o">,</span> <span class="n">x</span> <span class="bp">⊔</span> <span class="n">y</span> <span class="bp">⊓</span> <span class="n">z</span> <span class="bp">=</span> <span class="o">(</span><span class="n">x</span> <span class="bp">⊔</span> <span class="n">y</span><span class="o">)</span> <span class="bp">⊓</span> <span class="o">(</span><span class="n">x</span> <span class="bp">⊔</span> <span class="n">z</span><span class="o">))</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">⊓</span> <span class="o">(</span><span class="n">b</span> <span class="bp">⊔</span> <span class="n">c</span><span class="o">)</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">⊓</span> <span class="n">b</span> <span class="bp">⊔</span> <span class="n">a</span> <span class="bp">⊓</span> <span class="n">c</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>It is possible to combine axiomatic structures into larger ones.
-
@@ -1361,16 +1357,16 @@ For example, a <em>strict ordered ring</em> consists of a ring togetherwith a partial order on the carrier satisfying additional axioms that say that the ring operations are compatible with the order:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">R</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">StrictOrderedRing</span><span class="w"> </span><span class="n">R</span><span class="o">]</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">R</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">StrictOrderedRing</span> <span class="n">R</span><span class="o">]</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">add_le_add_left</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">c</span><span class="o">,</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">mul_pos</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">add_le_add_left</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">b</span> <span class="bp">→</span> <span class="bp">∀</span> <span class="n">c</span><span class="o">,</span> <span class="n">c</span> <span class="bp">+</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">c</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">mul_pos</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp"><</span> <span class="n">a</span> <span class="bp">→</span> <span class="mi">0</span> <span class="bp"><</span> <span class="n">b</span> <span class="bp">→</span> <span class="mi">0</span> <span class="bp"><</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">b</span><span class="o">)</span> </pre></div> </div> <p><a class="reference internal" href="C03_Logic.html#logic"><span class="std std-numref">Chapter 3</span></a> will provide the means to derive the following from <code class="docutils literal notranslate"><span class="pre">mul_pos</span></code> and the definition of <code class="docutils literal notranslate"><span class="pre"><</span></code>:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">mul_nonneg</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="o">(</span><span class="n">mul_nonneg</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp">≤</span> <span class="n">a</span> <span class="bp">→</span> <span class="mi">0</span> <span class="bp">≤</span> <span class="n">b</span> <span class="bp">→</span> <span class="mi">0</span> <span class="bp">≤</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">b</span><span class="o">)</span> </pre></div> </div> <p>It is then an extended exercise to show that many common facts
-
@@ -1380,14 +1376,14 @@ Here are a couple of examples you can try,using only properties of rings, partial orders, and the facts enumerated in the last two examples (beware that those rings are not assumed to be commutative, so the <cite>ring</cite> tactic is not available):</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">b</span><span class="o">)</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp">≤</span> <span class="n">b</span> <span class="bp">-</span> <span class="n">a</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">h</span><span class="o">:</span> <span class="mi">0</span> <span class="bp">≤</span> <span class="n">b</span> <span class="bp">-</span> <span class="n">a</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">b</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">c</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">b</span><span class="o">)</span> <span class="o">(</span><span class="n">h'</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp">≤</span> <span class="n">c</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">c</span> <span class="bp">≤</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">c</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p id="index-30">Finally, here is one last example.
-
@@ -1395,19 +1391,19 @@ A <em>metric space</em> consists of a set equipped with a notion ofdistance, <code class="docutils literal notranslate"><span class="pre">dist</span> <span class="pre">x</span> <span class="pre">y</span></code>, mapping any pair of elements to a real number. The distance function is assumed to satisfy the following axioms:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">X</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">MetricSpace</span><span class="w"> </span><span class="n">X</span><span class="o">]</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">X</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">MetricSpace</span> <span class="n">X</span><span class="o">]</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="n">z</span> <span class="o">:</span> <span class="n">X</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">dist_self</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">dist_comm</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">x</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">dist_triangle</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">z</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">dist_self</span> <span class="n">x</span> <span class="o">:</span> <span class="n">dist</span> <span class="n">x</span> <span class="n">x</span> <span class="bp">=</span> <span class="mi">0</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">dist_comm</span> <span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">dist</span> <span class="n">x</span> <span class="n">y</span> <span class="bp">=</span> <span class="n">dist</span> <span class="n">y</span> <span class="n">x</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">dist_triangle</span> <span class="n">x</span> <span class="n">y</span> <span class="n">z</span> <span class="o">:</span> <span class="n">dist</span> <span class="n">x</span> <span class="n">z</span> <span class="bp">≤</span> <span class="n">dist</span> <span class="n">x</span> <span class="n">y</span> <span class="bp">+</span> <span class="n">dist</span> <span class="n">y</span> <span class="n">z</span><span class="o">)</span> </pre></div> </div> <p>Having mastered this section, you can show that it follows from these axioms that distances are always nonnegative:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">X</span><span class="o">)</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp">≤</span> <span class="n">dist</span> <span class="n">x</span> <span class="n">y</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>We recommend making use of the theorem <code class="docutils literal notranslate"><span class="pre">nonneg_of_mul_nonneg_left</span></code>.
-
-
-
@@ -1,24 +1,24 @@<!DOCTYPE html> <html class="writer-html5" lang="en" data-content_root="./"> <html class="writer-html5" lang="en" > <head> <meta charset="utf-8" /><meta name="viewport" content="width=device-width, initial-scale=1" /> <meta charset="utf-8" /><meta name="generator" content="Docutils 0.17.1: http://docutils.sourceforge.net/" /> <meta name="viewport" content="width=device-width, initial-scale=1.0" /> <title>3. Logic — Mathematics in Lean 0.1 documentation</title> <link rel="stylesheet" type="text/css" href="_static/pygments.css?v=80d5e7a1" /> <link rel="stylesheet" type="text/css" href="_static/css/theme.css?v=e59714d7" /> <link rel="stylesheet" type="text/css" href="_static/css/custom.css?v=0731ccc3" /> <link rel="stylesheet" href="_static/pygments.css" type="text/css" /> <link rel="stylesheet" href="_static/css/theme.css" type="text/css" /> <link rel="stylesheet" href="_static/css/custom.css" type="text/css" /> <link rel="shortcut icon" href="_static/favicon.ico"/> <script src="_static/jquery.js?v=5d32c60e"></script> <script src="_static/_sphinx_javascript_frameworks_compat.js?v=2cd50e6c"></script> <script src="_static/documentation_options.js?v=2709fde1"></script> <script src="_static/doctools.js?v=9bcbadda"></script> <script src="_static/sphinx_highlight.js?v=dc90522c"></script> <script async="async" src="https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js"></script> <!--[if lt IE 9]> <script src="_static/js/html5shiv.min.js"></script> <![endif]--> <script data-url_root="./" id="documentation_options" src="_static/documentation_options.js"></script> <script src="_static/jquery.js"></script> <script src="_static/underscore.js"></script> <script src="_static/_sphinx_javascript_frameworks_compat.js"></script> <script src="_static/doctools.js"></script> <script async="async" src="https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js"></script> <script src="_static/js/theme.js"></script> <link rel="index" title="Index" href="genindex.html" /> <link rel="search" title="Search" href="search.html" />
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@@ -31,15 +31,11 @@<nav data-toggle="wy-nav-shift" class="wy-nav-side"> <div class="wy-side-scroll"> <div class="wy-side-nav-search" > <a href="index.html" class="icon icon-home"> Mathematics in Lean <a href="index.html" class="icon icon-home"> Mathematics in Lean </a> <div role="search"> <form id="rtd-search-form" class="wy-form" action="search.html" method="get"> <input type="text" name="q" placeholder="Search docs" aria-label="Search docs" /> <input type="text" name="q" placeholder="Search docs" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form>
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@@ -84,8 +80,8 @@<div class="rst-content"> <div role="navigation" aria-label="Page navigation"> <ul class="wy-breadcrumbs"> <li><a href="index.html" class="icon icon-home" aria-label="Home"></a></li> <li class="breadcrumb-item active"><span class="section-number">3. </span>Logic</li> <li><a href="index.html" class="icon icon-home"></a> »</li> <li><span class="section-number">3. </span>Logic</li> <li class="wy-breadcrumbs-aside"> <a href="_sources/C03_Logic.rst.txt" rel="nofollow"> View page source</a> </li>
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@@ -96,7 +92,7 @@<div itemprop="articleBody"> <section id="logic"> <span id="id1"></span><h1><span class="section-number">3. </span>Logic<a class="headerlink" href="#logic" title="Link to this heading"></a></h1> <span id="id1"></span><h1><span class="section-number">3. </span>Logic<a class="headerlink" href="#logic" title="Permalink to this heading"></a></h1> <p>In the last chapter, we dealt with equations, inequalities, and basic mathematical statements like “<span class="math notranslate nohighlight">\(x\)</span> divides <span class="math notranslate nohighlight">\(y\)</span>.”
-
@@ -107,15 +103,15 @@ using logical terms like “and,” “or,” “not,”In this chapter, we show you how to work with statements that are built up in this way.</p> <section id="implication-and-the-universal-quantifier"> <span id="id2"></span><h2><span class="section-number">3.1. </span>Implication and the Universal Quantifier<a class="headerlink" href="#implication-and-the-universal-quantifier" title="Link to this heading"></a></h2> <span id="id2"></span><h2><span class="section-number">3.1. </span>Implication and the Universal Quantifier<a class="headerlink" href="#implication-and-the-universal-quantifier" title="Permalink to this heading"></a></h2> <p>Consider the statement after the <code class="docutils literal notranslate"><span class="pre">#check</span></code>:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">,</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="bp">|</span><span class="n">x</span><span class="bp">|</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="bp">∀</span> <span class="n">x</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">,</span> <span class="mi">0</span> <span class="bp">≤</span> <span class="n">x</span> <span class="bp">→</span> <span class="bp">|</span><span class="n">x</span><span class="bp">|</span> <span class="bp">=</span> <span class="n">x</span> </pre></div> </div> <p>In words, we would say “for every real number <code class="docutils literal notranslate"><span class="pre">x</span></code>, if <code class="docutils literal notranslate"><span class="pre">0</span> <span class="pre">≤</span> <span class="pre">x</span></code> then the absolute value of <code class="docutils literal notranslate"><span class="pre">x</span></code> equals <code class="docutils literal notranslate"><span class="pre">x</span></code>”. We can also have more complicated statements like:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">,</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="bp">|</span><span class="n">x</span><span class="bp">|</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="bp">|</span><span class="n">y</span><span class="bp">|</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="bp">|</span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y</span><span class="bp">|</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="bp">∀</span> <span class="n">x</span> <span class="n">y</span> <span class="n">ε</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">,</span> <span class="mi">0</span> <span class="bp"><</span> <span class="n">ε</span> <span class="bp">→</span> <span class="n">ε</span> <span class="bp">≤</span> <span class="mi">1</span> <span class="bp">→</span> <span class="bp">|</span><span class="n">x</span><span class="bp">|</span> <span class="bp"><</span> <span class="n">ε</span> <span class="bp">→</span> <span class="bp">|</span><span class="n">y</span><span class="bp">|</span> <span class="bp"><</span> <span class="n">ε</span> <span class="bp">→</span> <span class="bp">|</span><span class="n">x</span> <span class="bp">*</span> <span class="n">y</span><span class="bp">|</span> <span class="bp"><</span> <span class="n">ε</span> </pre></div> </div> <p>In words, we would say “for every <code class="docutils literal notranslate"><span class="pre">x</span></code>, <code class="docutils literal notranslate"><span class="pre">y</span></code>, and <code class="docutils literal notranslate"><span class="pre">ε</span></code>,
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@@ -136,17 +132,17 @@ In particular, if you have proved a theorem of that form,you can apply it to objects and hypotheses in the same way. We will use as an example the following statement that we will help you to prove a bit later:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">my_lemma</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">,</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="bp">|</span><span class="n">x</span><span class="bp">|</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="bp">|</span><span class="n">y</span><span class="bp">|</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="bp">|</span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y</span><span class="bp">|</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">my_lemma</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span> <span class="n">y</span> <span class="n">ε</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">,</span> <span class="mi">0</span> <span class="bp"><</span> <span class="n">ε</span> <span class="bp">→</span> <span class="n">ε</span> <span class="bp">≤</span> <span class="mi">1</span> <span class="bp">→</span> <span class="bp">|</span><span class="n">x</span><span class="bp">|</span> <span class="bp"><</span> <span class="n">ε</span> <span class="bp">→</span> <span class="bp">|</span><span class="n">y</span><span class="bp">|</span> <span class="bp"><</span> <span class="n">ε</span> <span class="bp">→</span> <span class="bp">|</span><span class="n">x</span> <span class="bp">*</span> <span class="n">y</span><span class="bp">|</span> <span class="bp"><</span> <span class="n">ε</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="kn">section</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">δ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">h₀</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">δ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h₁</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">δ</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">ha</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">|</span><span class="n">a</span><span class="bp">|</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">δ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hb</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">|</span><span class="n">b</span><span class="bp">|</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">δ</span><span class="o">)</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="n">δ</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">h₀</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp"><</span> <span class="n">δ</span><span class="o">)</span> <span class="o">(</span><span class="n">h₁</span> <span class="o">:</span> <span class="n">δ</span> <span class="bp">≤</span> <span class="mi">1</span><span class="o">)</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">ha</span> <span class="o">:</span> <span class="bp">|</span><span class="n">a</span><span class="bp">|</span> <span class="bp"><</span> <span class="n">δ</span><span class="o">)</span> <span class="o">(</span><span class="n">hb</span> <span class="o">:</span> <span class="bp">|</span><span class="n">b</span><span class="bp">|</span> <span class="bp"><</span> <span class="n">δ</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="n">my_lemma</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">δ</span> <span class="k">#check</span><span class="w"> </span><span class="n">my_lemma</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">δ</span><span class="w"> </span><span class="n">h₀</span><span class="w"> </span><span class="n">h₁</span> <span class="k">#check</span><span class="w"> </span><span class="n">my_lemma</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">δ</span><span class="w"> </span><span class="n">h₀</span><span class="w"> </span><span class="n">h₁</span><span class="w"> </span><span class="n">ha</span><span class="w"> </span><span class="n">hb</span> <span class="k">#check</span> <span class="n">my_lemma</span> <span class="n">a</span> <span class="n">b</span> <span class="n">δ</span> <span class="k">#check</span> <span class="n">my_lemma</span> <span class="n">a</span> <span class="n">b</span> <span class="n">δ</span> <span class="n">h₀</span> <span class="n">h₁</span> <span class="k">#check</span> <span class="n">my_lemma</span> <span class="n">a</span> <span class="n">b</span> <span class="n">δ</span> <span class="n">h₀</span> <span class="n">h₁</span> <span class="n">ha</span> <span class="n">hb</span> <span class="kd">end</span> </pre></div>
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@@ -156,15 +152,15 @@ to use curly brackets to make quantified variables implicitwhen they can be inferred from subsequent hypotheses. When we do that, we can just apply a lemma to the hypotheses without mentioning the objects.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">my_lemma2</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">},</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="bp">|</span><span class="n">x</span><span class="bp">|</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="bp">|</span><span class="n">y</span><span class="bp">|</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="bp">|</span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y</span><span class="bp">|</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">my_lemma2</span> <span class="o">:</span> <span class="bp">∀</span> <span class="o">{</span><span class="n">x</span> <span class="n">y</span> <span class="n">ε</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">},</span> <span class="mi">0</span> <span class="bp"><</span> <span class="n">ε</span> <span class="bp">→</span> <span class="n">ε</span> <span class="bp">≤</span> <span class="mi">1</span> <span class="bp">→</span> <span class="bp">|</span><span class="n">x</span><span class="bp">|</span> <span class="bp"><</span> <span class="n">ε</span> <span class="bp">→</span> <span class="bp">|</span><span class="n">y</span><span class="bp">|</span> <span class="bp"><</span> <span class="n">ε</span> <span class="bp">→</span> <span class="bp">|</span><span class="n">x</span> <span class="bp">*</span> <span class="n">y</span><span class="bp">|</span> <span class="bp"><</span> <span class="n">ε</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="kn">section</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">δ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">h₀</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">δ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h₁</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">δ</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">ha</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">|</span><span class="n">a</span><span class="bp">|</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">δ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hb</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">|</span><span class="n">b</span><span class="bp">|</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">δ</span><span class="o">)</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="n">δ</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">h₀</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp"><</span> <span class="n">δ</span><span class="o">)</span> <span class="o">(</span><span class="n">h₁</span> <span class="o">:</span> <span class="n">δ</span> <span class="bp">≤</span> <span class="mi">1</span><span class="o">)</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">ha</span> <span class="o">:</span> <span class="bp">|</span><span class="n">a</span><span class="bp">|</span> <span class="bp"><</span> <span class="n">δ</span><span class="o">)</span> <span class="o">(</span><span class="n">hb</span> <span class="o">:</span> <span class="bp">|</span><span class="n">b</span><span class="bp">|</span> <span class="bp"><</span> <span class="n">δ</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="n">my_lemma2</span><span class="w"> </span><span class="n">h₀</span><span class="w"> </span><span class="n">h₁</span><span class="w"> </span><span class="n">ha</span><span class="w"> </span><span class="n">hb</span> <span class="k">#check</span> <span class="n">my_lemma2</span> <span class="n">h₀</span> <span class="n">h₁</span> <span class="n">ha</span> <span class="n">hb</span> <span class="kd">end</span> </pre></div>
-
@@ -172,14 +168,14 @@ mentioning the objects.</p><p>At this stage, you also know that if you use the <code class="docutils literal notranslate"><span class="pre">apply</span></code> tactic to apply <code class="docutils literal notranslate"><span class="pre">my_lemma</span></code> to a goal of the form <code class="docutils literal notranslate"><span class="pre">|a</span> <span class="pre">*</span> <span class="pre">b|</span> <span class="pre"><</span> <span class="pre">δ</span></code>, you are left with new goals that require you to prove you are left with new goals that require you to prove each of the hypotheses.</p> <p id="index-0">To prove a statement like this, use the <code class="docutils literal notranslate"><span class="pre">intro</span></code> tactic. Take a look at what it does in this example:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">my_lemma3</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">},</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="bp">|</span><span class="n">x</span><span class="bp">|</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="bp">|</span><span class="n">y</span><span class="bp">|</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="bp">|</span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y</span><span class="bp">|</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="n">epos</span><span class="w"> </span><span class="n">ele1</span><span class="w"> </span><span class="n">xlt</span><span class="w"> </span><span class="n">ylt</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">my_lemma3</span> <span class="o">:</span> <span class="bp">∀</span> <span class="o">{</span><span class="n">x</span> <span class="n">y</span> <span class="n">ε</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">},</span> <span class="mi">0</span> <span class="bp"><</span> <span class="n">ε</span> <span class="bp">→</span> <span class="n">ε</span> <span class="bp">≤</span> <span class="mi">1</span> <span class="bp">→</span> <span class="bp">|</span><span class="n">x</span><span class="bp">|</span> <span class="bp"><</span> <span class="n">ε</span> <span class="bp">→</span> <span class="bp">|</span><span class="n">y</span><span class="bp">|</span> <span class="bp"><</span> <span class="n">ε</span> <span class="bp">→</span> <span class="bp">|</span><span class="n">x</span> <span class="bp">*</span> <span class="n">y</span><span class="bp">|</span> <span class="bp"><</span> <span class="n">ε</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">x</span> <span class="n">y</span> <span class="n">ε</span> <span class="n">epos</span> <span class="n">ele1</span> <span class="n">xlt</span> <span class="n">ylt</span> <span class="gr">sorry</span> </pre></div> </div> <p>We can use any names we want for the universally quantified variables;
-
@@ -197,14 +193,14 @@ as we did in the last section.In a moment, we will see why it is sometimes necessary to introduce variables and hypotheses after the proof begins.</p> <p>To help you prove the lemma, we will start you off:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">my_lemma4</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">},</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="bp">|</span><span class="n">x</span><span class="bp">|</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="bp">|</span><span class="n">y</span><span class="bp">|</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="bp">|</span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y</span><span class="bp">|</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="n">epos</span><span class="w"> </span><span class="n">ele1</span><span class="w"> </span><span class="n">xlt</span><span class="w"> </span><span class="n">ylt</span> <span class="w"> </span><span class="k">calc</span> <span class="w"> </span><span class="bp">|</span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y</span><span class="bp">|</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">|</span><span class="n">x</span><span class="bp">|</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="bp">|</span><span class="n">y</span><span class="bp">|</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="bp">|</span><span class="n">x</span><span class="bp">|</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">my_lemma4</span> <span class="o">:</span> <span class="bp">∀</span> <span class="o">{</span><span class="n">x</span> <span class="n">y</span> <span class="n">ε</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">},</span> <span class="mi">0</span> <span class="bp"><</span> <span class="n">ε</span> <span class="bp">→</span> <span class="n">ε</span> <span class="bp">≤</span> <span class="mi">1</span> <span class="bp">→</span> <span class="bp">|</span><span class="n">x</span><span class="bp">|</span> <span class="bp"><</span> <span class="n">ε</span> <span class="bp">→</span> <span class="bp">|</span><span class="n">y</span><span class="bp">|</span> <span class="bp"><</span> <span class="n">ε</span> <span class="bp">→</span> <span class="bp">|</span><span class="n">x</span> <span class="bp">*</span> <span class="n">y</span><span class="bp">|</span> <span class="bp"><</span> <span class="n">ε</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">x</span> <span class="n">y</span> <span class="n">ε</span> <span class="n">epos</span> <span class="n">ele1</span> <span class="n">xlt</span> <span class="n">ylt</span> <span class="k">calc</span> <span class="bp">|</span><span class="n">x</span> <span class="bp">*</span> <span class="n">y</span><span class="bp">|</span> <span class="bp">=</span> <span class="bp">|</span><span class="n">x</span><span class="bp">|</span> <span class="bp">*</span> <span class="bp">|</span><span class="n">y</span><span class="bp">|</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="n">_</span> <span class="bp">≤</span> <span class="bp">|</span><span class="n">x</span><span class="bp">|</span> <span class="bp">*</span> <span class="n">ε</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="n">_</span> <span class="bp"><</span> <span class="mi">1</span> <span class="bp">*</span> <span class="n">ε</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="n">_</span> <span class="bp">=</span> <span class="n">ε</span> <span class="o">:=</span> <span class="gr">sorry</span> </pre></div> </div> <p>Finish the proof using the theorems
-
@@ -225,22 +221,22 @@ The first says that <code class="docutils literal notranslate"><span class="pre"values of <code class="docutils literal notranslate"><span class="pre">f</span></code>, and the second says that <code class="docutils literal notranslate"><span class="pre">a</span></code> is a lower bound on the values of <code class="docutils literal notranslate"><span class="pre">f</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">FnUb</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Prop</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">a</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">FnUb</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="kt">Prop</span> <span class="o">:=</span> <span class="bp">∀</span> <span class="n">x</span><span class="o">,</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">a</span> <span class="kd">def</span><span class="w"> </span><span class="n">FnLb</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Prop</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span> <span class="kd">def</span> <span class="n">FnLb</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="kt">Prop</span> <span class="o">:=</span> <span class="bp">∀</span> <span class="n">x</span><span class="o">,</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">f</span> <span class="n">x</span> </pre></div> </div> <p id="index-1">In the next example, <code class="docutils literal notranslate"><span class="pre">fun</span> <span class="pre">x</span> <span class="pre">↦</span> <span class="pre">f</span> <span class="pre">x</span> <span class="pre">+</span> <span class="pre">g</span> <span class="pre">x</span></code> is the function that maps <code class="docutils literal notranslate"><span class="pre">x</span></code> to <code class="docutils literal notranslate"><span class="pre">f</span> <span class="pre">x</span> <span class="pre">+</span> <span class="pre">g</span> <span class="pre">x</span></code>. Going from the expression <code class="docutils literal notranslate"><span class="pre">f</span> <span class="pre">x</span> <span class="pre">+</span> <span class="pre">g</span> <span class="pre">x</span></code> to this function is called a lambda abstraction in type theory.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">hfa</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnUb</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hgb</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnUb</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnUb</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">x</span> <span class="w"> </span><span class="n">dsimp</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">add_le_add</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">hfa</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">hgb</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">hfa</span> <span class="o">:</span> <span class="n">FnUb</span> <span class="n">f</span> <span class="n">a</span><span class="o">)</span> <span class="o">(</span><span class="n">hgb</span> <span class="o">:</span> <span class="n">FnUb</span> <span class="n">g</span> <span class="n">b</span><span class="o">)</span> <span class="o">:</span> <span class="n">FnUb</span> <span class="o">(</span><span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">g</span> <span class="n">x</span><span class="o">)</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">x</span> <span class="n">dsimp</span> <span class="n">apply</span> <span class="n">add_le_add</span> <span class="n">apply</span> <span class="n">hfa</span> <span class="n">apply</span> <span class="n">hgb</span> </pre></div> </div> <p id="index-2">Applying <code class="docutils literal notranslate"><span class="pre">intro</span></code> to the goal <code class="docutils literal notranslate"><span class="pre">FnUb</span> <span class="pre">(fun</span> <span class="pre">x</span> <span class="pre">↦</span> <span class="pre">f</span> <span class="pre">x</span> <span class="pre">+</span> <span class="pre">g</span> <span class="pre">x)</span> <span class="pre">(a</span> <span class="pre">+</span> <span class="pre">b)</span></code>
-
@@ -263,15 +259,15 @@ and gives you more control over how the goal is transformed.</p>The last two <code class="docutils literal notranslate"><span class="pre">apply</span></code> commands force Lean to unfold the definitions of <code class="docutils literal notranslate"><span class="pre">FnUb</span></code> in the hypotheses. Try carrying out similar proofs of these:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">hfa</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnLb</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hgb</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnLb</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnLb</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">hfa</span> <span class="o">:</span> <span class="n">FnLb</span> <span class="n">f</span> <span class="n">a</span><span class="o">)</span> <span class="o">(</span><span class="n">hgb</span> <span class="o">:</span> <span class="n">FnLb</span> <span class="n">g</span> <span class="n">b</span><span class="o">)</span> <span class="o">:</span> <span class="n">FnLb</span> <span class="o">(</span><span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">g</span> <span class="n">x</span><span class="o">)</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">nnf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnLb</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">nng</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnLb</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnLb</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">nnf</span> <span class="o">:</span> <span class="n">FnLb</span> <span class="n">f</span> <span class="mi">0</span><span class="o">)</span> <span class="o">(</span><span class="n">nng</span> <span class="o">:</span> <span class="n">FnLb</span> <span class="n">g</span> <span class="mi">0</span><span class="o">)</span> <span class="o">:</span> <span class="n">FnLb</span> <span class="o">(</span><span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">*</span> <span class="n">g</span> <span class="n">x</span><span class="o">)</span> <span class="mi">0</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">hfa</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnUb</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hgb</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnUb</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">nng</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnLb</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">nna</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">FnUb</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">hfa</span> <span class="o">:</span> <span class="n">FnUb</span> <span class="n">f</span> <span class="n">a</span><span class="o">)</span> <span class="o">(</span><span class="n">hgb</span> <span class="o">:</span> <span class="n">FnUb</span> <span class="n">g</span> <span class="n">b</span><span class="o">)</span> <span class="o">(</span><span class="n">nng</span> <span class="o">:</span> <span class="n">FnLb</span> <span class="n">g</span> <span class="mi">0</span><span class="o">)</span> <span class="o">(</span><span class="n">nna</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp">≤</span> <span class="n">a</span><span class="o">)</span> <span class="o">:</span> <span class="n">FnUb</span> <span class="o">(</span><span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">*</span> <span class="n">g</span> <span class="n">x</span><span class="o">)</span> <span class="o">(</span><span class="n">a</span> <span class="bp">*</span> <span class="n">b</span><span class="o">)</span> <span class="o">:=</span> <span class="gr">sorry</span> </pre></div> </div> <p>Even though we have defined <code class="docutils literal notranslate"><span class="pre">FnUb</span></code> and <code class="docutils literal notranslate"><span class="pre">FnLb</span></code> for functions
-
@@ -287,15 +283,15 @@ but it is worth knowing that the natural numbers, integers, rationals,and real numbers are all instances. So if we prove the theorem <code class="docutils literal notranslate"><span class="pre">fnUb_add</span></code> at that level of generality, it will apply in all these instances.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">R</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">OrderedCancelAddCommMonoid</span><span class="w"> </span><span class="n">R</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">{</span><span class="n">R</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">OrderedCancelAddCommMonoid</span> <span class="n">R</span><span class="o">]</span> <span class="k">#check</span><span class="w"> </span><span class="n">add_le_add</span> <span class="k">#check</span> <span class="n">add_le_add</span> <span class="kd">def</span><span class="w"> </span><span class="n">FnUb'</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Prop</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">a</span> <span class="kd">def</span> <span class="n">FnUb'</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">R</span><span class="o">)</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="o">:</span> <span class="kt">Prop</span> <span class="o">:=</span> <span class="bp">∀</span> <span class="n">x</span><span class="o">,</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">a</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">fnUb_add</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">R</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hfa</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnUb'</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hgb</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnUb'</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">FnUb'</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">add_le_add</span><span class="w"> </span><span class="o">(</span><span class="n">hfa</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hgb</span><span class="w"> </span><span class="n">x</span><span class="o">)</span> <span class="kd">theorem</span> <span class="n">fnUb_add</span> <span class="o">{</span><span class="n">f</span> <span class="n">g</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">R</span><span class="o">}</span> <span class="o">{</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">R</span><span class="o">}</span> <span class="o">(</span><span class="n">hfa</span> <span class="o">:</span> <span class="n">FnUb'</span> <span class="n">f</span> <span class="n">a</span><span class="o">)</span> <span class="o">(</span><span class="n">hgb</span> <span class="o">:</span> <span class="n">FnUb'</span> <span class="n">g</span> <span class="n">b</span><span class="o">)</span> <span class="o">:</span> <span class="n">FnUb'</span> <span class="o">(</span><span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">g</span> <span class="n">x</span><span class="o">)</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">add_le_add</span> <span class="o">(</span><span class="n">hfa</span> <span class="n">x</span><span class="o">)</span> <span class="o">(</span><span class="n">hgb</span> <span class="n">x</span><span class="o">)</span> </pre></div> </div> <p>You have already seen square brackets like these in
-
@@ -308,8 +304,8 @@ that work at a high level of generality.</p><p id="index-3">For another example of a hidden universal quantifier, Mathlib defines a predicate <code class="docutils literal notranslate"><span class="pre">Monotone</span></code>, which says that a function is nondecreasing in its arguments:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Monotone</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="o">},</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="bp">@</span><span class="n">h</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">Monotone</span> <span class="n">f</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∀</span> <span class="o">{</span><span class="n">a</span> <span class="n">b</span><span class="o">},</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">b</span> <span class="bp">→</span> <span class="n">f</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">f</span> <span class="n">b</span> <span class="o">:=</span> <span class="bp">@</span><span class="n">h</span> </pre></div> </div> <p>The property <code class="docutils literal notranslate"><span class="pre">Monotone</span> <span class="pre">f</span></code> is defined to be exactly the expression
-
@@ -325,11 +321,11 @@ and then apply the resulting expression to the goal.Or you can apply it to the goal and let Lean help you work backwards by displaying the remaining hypotheses as new subgoals.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">mf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Monotone</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">mg</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Monotone</span><span class="w"> </span><span class="n">g</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Monotone</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">aleb</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">add_le_add</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">mf</span><span class="w"> </span><span class="n">aleb</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">mg</span><span class="w"> </span><span class="n">aleb</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">mf</span> <span class="o">:</span> <span class="n">Monotone</span> <span class="n">f</span><span class="o">)</span> <span class="o">(</span><span class="n">mg</span> <span class="o">:</span> <span class="n">Monotone</span> <span class="n">g</span><span class="o">)</span> <span class="o">:</span> <span class="n">Monotone</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">g</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">a</span> <span class="n">b</span> <span class="n">aleb</span> <span class="n">apply</span> <span class="n">add_le_add</span> <span class="n">apply</span> <span class="n">mf</span> <span class="n">aleb</span> <span class="n">apply</span> <span class="n">mg</span> <span class="n">aleb</span> </pre></div> </div> <p>When a proof is this short, it is often convenient
-
@@ -345,8 +341,8 @@ So the <code class="docutils literal notranslate"><span class="pre">intro</span>corresponds to the lambda abstraction in the next proof term. The <code class="docutils literal notranslate"><span class="pre">apply</span></code> commands then correspond to building the application of the theorem to its arguments.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">mf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Monotone</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">mg</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Monotone</span><span class="w"> </span><span class="n">g</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Monotone</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">aleb</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">add_le_add</span><span class="w"> </span><span class="o">(</span><span class="n">mf</span><span class="w"> </span><span class="n">aleb</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">mg</span><span class="w"> </span><span class="n">aleb</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">mf</span> <span class="o">:</span> <span class="n">Monotone</span> <span class="n">f</span><span class="o">)</span> <span class="o">(</span><span class="n">mg</span> <span class="o">:</span> <span class="n">Monotone</span> <span class="n">g</span><span class="o">)</span> <span class="o">:</span> <span class="n">Monotone</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">g</span> <span class="n">x</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">a</span> <span class="n">b</span> <span class="n">aleb</span> <span class="bp">↦</span> <span class="n">add_le_add</span> <span class="o">(</span><span class="n">mf</span> <span class="n">aleb</span><span class="o">)</span> <span class="o">(</span><span class="n">mg</span> <span class="n">aleb</span><span class="o">)</span> </pre></div> </div> <p>Here is a useful trick: if you start writing
-
@@ -360,11 +356,11 @@ hover over the squiggly error marker,Lean will show you the goal that the remaining expression has to solve.</p> <p>Try proving these, with either tactics or proof terms:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">mf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Monotone</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">nnc</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">c</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Monotone</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">c</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">mf</span> <span class="o">:</span> <span class="n">Monotone</span> <span class="n">f</span><span class="o">)</span> <span class="o">(</span><span class="n">nnc</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp">≤</span> <span class="n">c</span><span class="o">)</span> <span class="o">:</span> <span class="n">Monotone</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">c</span> <span class="bp">*</span> <span class="n">f</span> <span class="n">x</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">mf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Monotone</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">mg</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Monotone</span><span class="w"> </span><span class="n">g</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Monotone</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">g</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">mf</span> <span class="o">:</span> <span class="n">Monotone</span> <span class="n">f</span><span class="o">)</span> <span class="o">(</span><span class="n">mg</span> <span class="o">:</span> <span class="n">Monotone</span> <span class="n">g</span><span class="o">)</span> <span class="o">:</span> <span class="n">Monotone</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">f</span> <span class="o">(</span><span class="n">g</span> <span class="n">x</span><span class="o">)</span> <span class="o">:=</span> <span class="gr">sorry</span> </pre></div> </div> <p>Here are some more examples.
-
@@ -375,27 +371,27 @@ and <em>odd</em> if <span class="math notranslate nohighlight">\(f(-x) = -f(x)\)The following example defines these two notions formally and establishes one fact about them. You can complete the proofs of the others.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">FnEven</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Prop</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="bp">-</span><span class="n">x</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">FnEven</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="kt">Prop</span> <span class="o">:=</span> <span class="bp">∀</span> <span class="n">x</span><span class="o">,</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">=</span> <span class="n">f</span> <span class="o">(</span><span class="bp">-</span><span class="n">x</span><span class="o">)</span> <span class="kd">def</span><span class="w"> </span><span class="n">FnOdd</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Prop</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">-</span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="bp">-</span><span class="n">x</span><span class="o">)</span> <span class="kd">def</span> <span class="n">FnOdd</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="kt">Prop</span> <span class="o">:=</span> <span class="bp">∀</span> <span class="n">x</span><span class="o">,</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">=</span> <span class="bp">-</span><span class="n">f</span> <span class="o">(</span><span class="bp">-</span><span class="n">x</span><span class="o">)</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">ef</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnEven</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">eg</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnEven</span><span class="w"> </span><span class="n">g</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnEven</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">x</span> <span class="w"> </span><span class="k">calc</span> <span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">rfl</span> <span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="bp">-</span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="o">(</span><span class="bp">-</span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">ef</span><span class="o">,</span><span class="w"> </span><span class="n">eg</span><span class="o">]</span> <span class="kd">example</span> <span class="o">(</span><span class="n">ef</span> <span class="o">:</span> <span class="n">FnEven</span> <span class="n">f</span><span class="o">)</span> <span class="o">(</span><span class="n">eg</span> <span class="o">:</span> <span class="n">FnEven</span> <span class="n">g</span><span class="o">)</span> <span class="o">:</span> <span class="n">FnEven</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">g</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">x</span> <span class="k">calc</span> <span class="o">(</span><span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">g</span> <span class="n">x</span><span class="o">)</span> <span class="n">x</span> <span class="bp">=</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">g</span> <span class="n">x</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="n">_</span> <span class="bp">=</span> <span class="n">f</span> <span class="o">(</span><span class="bp">-</span><span class="n">x</span><span class="o">)</span> <span class="bp">+</span> <span class="n">g</span> <span class="o">(</span><span class="bp">-</span><span class="n">x</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">ef</span><span class="o">,</span> <span class="n">eg</span><span class="o">]</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">of</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnOdd</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">og</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnOdd</span><span class="w"> </span><span class="n">g</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnEven</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">of</span> <span class="o">:</span> <span class="n">FnOdd</span> <span class="n">f</span><span class="o">)</span> <span class="o">(</span><span class="n">og</span> <span class="o">:</span> <span class="n">FnOdd</span> <span class="n">g</span><span class="o">)</span> <span class="o">:</span> <span class="n">FnEven</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">*</span> <span class="n">g</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">ef</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnEven</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">og</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnOdd</span><span class="w"> </span><span class="n">g</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnOdd</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">ef</span> <span class="o">:</span> <span class="n">FnEven</span> <span class="n">f</span><span class="o">)</span> <span class="o">(</span><span class="n">og</span> <span class="o">:</span> <span class="n">FnOdd</span> <span class="n">g</span><span class="o">)</span> <span class="o">:</span> <span class="n">FnOdd</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">*</span> <span class="n">g</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">ef</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnEven</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">og</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnOdd</span><span class="w"> </span><span class="n">g</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnEven</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">g</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">ef</span> <span class="o">:</span> <span class="n">FnEven</span> <span class="n">f</span><span class="o">)</span> <span class="o">(</span><span class="n">og</span> <span class="o">:</span> <span class="n">FnOdd</span> <span class="n">g</span><span class="o">)</span> <span class="o">:</span> <span class="n">FnEven</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">f</span> <span class="o">(</span><span class="n">g</span> <span class="n">x</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p id="index-4">The first proof can be shortened using <code class="docutils literal notranslate"><span class="pre">dsimp</span></code> or <code class="docutils literal notranslate"><span class="pre">change</span></code>
-
@@ -435,16 +431,16 @@ we can write <code class="docutils literal notranslate"><span class="pre">h</spaThe following example provides a tactic proof and a proof term justifying the reflexivity of the subset relation, and asks you to do the same for transitivity.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">r</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">α</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">(</span><span class="n">r</span> <span class="n">s</span> <span class="n">t</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">α</span><span class="o">)</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">xs</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">xs</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">s</span> <span class="bp">⊆</span> <span class="n">s</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">x</span> <span class="n">xs</span> <span class="n">exact</span> <span class="n">xs</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">Subset.refl</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">xs</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">xs</span> <span class="kd">theorem</span> <span class="n">Subset.refl</span> <span class="o">:</span> <span class="n">s</span> <span class="bp">⊆</span> <span class="n">s</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">x</span> <span class="n">xs</span> <span class="bp">↦</span> <span class="n">xs</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">Subset.trans</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">theorem</span> <span class="n">Subset.trans</span> <span class="o">:</span> <span class="n">r</span> <span class="bp">⊆</span> <span class="n">s</span> <span class="bp">→</span> <span class="n">s</span> <span class="bp">⊆</span> <span class="n">t</span> <span class="bp">→</span> <span class="n">r</span> <span class="bp">⊆</span> <span class="n">t</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>Just as we defined <code class="docutils literal notranslate"><span class="pre">FnUb</span></code> for functions,
-
@@ -455,14 +451,14 @@ has an order associated with it.In the next example, we ask you to prove that if <code class="docutils literal notranslate"><span class="pre">a</span></code> is a bound on <code class="docutils literal notranslate"><span class="pre">s</span></code> and <code class="docutils literal notranslate"><span class="pre">a</span> <span class="pre">≤</span> <span class="pre">b</span></code>, then <code class="docutils literal notranslate"><span class="pre">b</span></code> is a bound on <code class="docutils literal notranslate"><span class="pre">s</span></code> as well.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">PartialOrder</span><span class="w"> </span><span class="n">α</span><span class="o">]</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">α</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">PartialOrder</span> <span class="n">α</span><span class="o">]</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">s</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">α</span><span class="o">)</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">α</span><span class="o">)</span> <span class="kd">def</span><span class="w"> </span><span class="n">SetUb</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">α</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">a</span> <span class="kd">def</span> <span class="n">SetUb</span> <span class="o">(</span><span class="n">s</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">α</span><span class="o">)</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">α</span><span class="o">)</span> <span class="o">:=</span> <span class="bp">∀</span> <span class="n">x</span><span class="o">,</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">s</span> <span class="bp">→</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">a</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">SetUb</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">SetUb</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">SetUb</span> <span class="n">s</span> <span class="n">a</span><span class="o">)</span> <span class="o">(</span><span class="n">h'</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">b</span><span class="o">)</span> <span class="o">:</span> <span class="n">SetUb</span> <span class="n">s</span> <span class="n">b</span> <span class="o">:=</span> <span class="gr">sorry</span> </pre></div> </div> <p id="index-5">We close this section with one last important example.
-
@@ -477,27 +473,27 @@ We then ask you to show that multiplication by a nonzeroconstant is also injective, using the lemma name in the example as a source of inspiration. Recall you should use Ctrl-space completion after guessing the beginning of a lemma name.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span><span class="w"> </span><span class="n">Function</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span> <span class="n">Function</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Injective</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">x₁</span><span class="w"> </span><span class="n">x₂</span><span class="w"> </span><span class="n">h'</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="o">(</span><span class="n">add_left_inj</span><span class="w"> </span><span class="n">c</span><span class="o">)</span><span class="bp">.</span><span class="n">mp</span><span class="w"> </span><span class="n">h'</span> <span class="kd">example</span> <span class="o">(</span><span class="n">c</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="n">Injective</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">c</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">x₁</span> <span class="n">x₂</span> <span class="n">h'</span> <span class="n">exact</span> <span class="o">(</span><span class="n">add_left_inj</span> <span class="n">c</span><span class="o">)</span><span class="bp">.</span><span class="n">mp</span> <span class="n">h'</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Injective</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">{</span><span class="n">c</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">c</span> <span class="bp">≠</span> <span class="mi">0</span><span class="o">)</span> <span class="o">:</span> <span class="n">Injective</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">c</span> <span class="bp">*</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>Finally, show that the composition of two injective functions is injective:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">β</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">γ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">g</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">β</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">γ</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">β</span><span class="o">}</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">{</span><span class="n">β</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">{</span><span class="n">γ</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="kd">variable</span> <span class="o">{</span><span class="n">g</span> <span class="o">:</span> <span class="n">β</span> <span class="bp">→</span> <span class="n">γ</span><span class="o">}</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">β</span><span class="o">}</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">injg</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Injective</span><span class="w"> </span><span class="n">g</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">injf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Injective</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Injective</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">injg</span> <span class="o">:</span> <span class="n">Injective</span> <span class="n">g</span><span class="o">)</span> <span class="o">(</span><span class="n">injf</span> <span class="o">:</span> <span class="n">Injective</span> <span class="n">f</span><span class="o">)</span> <span class="o">:</span> <span class="n">Injective</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">g</span> <span class="o">(</span><span class="n">f</span> <span class="n">x</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> </section> <section id="the-existential-quantifier"> <span id="id3"></span><h2><span class="section-number">3.2. </span>The Existential Quantifier<a class="headerlink" href="#the-existential-quantifier" title="Link to this heading"></a></h2> <span id="id3"></span><h2><span class="section-number">3.2. </span>The Existential Quantifier<a class="headerlink" href="#the-existential-quantifier" title="Permalink to this heading"></a></h2> <p>The existential quantifier, which can be entered as <code class="docutils literal notranslate"><span class="pre">\ex</span></code> in VS Code, is used to represent the phrase “there exists.” The formal expression <code class="docutils literal notranslate"><span class="pre">∃</span> <span class="pre">x</span> <span class="pre">:</span> <span class="pre">ℝ,</span> <span class="pre">2</span> <span class="pre"><</span> <span class="pre">x</span> <span class="pre">∧</span> <span class="pre">x</span> <span class="pre"><</span> <span class="pre">3</span></code> in Lean says
-
@@ -513,29 +509,29 @@ and the <code class="docutils literal notranslate"><span class="pre">norm_num</sGiven a goal that begins with an existential quantifier, the <code class="docutils literal notranslate"><span class="pre">use</span></code> tactic is used to provide the object, leaving the goal of proving the property.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">,</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span> <span class="w"> </span><span class="n">norm_num</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">x</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">,</span> <span class="mi">2</span> <span class="bp"><</span> <span class="n">x</span> <span class="bp">∧</span> <span class="n">x</span> <span class="bp"><</span> <span class="mi">3</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">use</span> <span class="mi">5</span> <span class="bp">/</span> <span class="mi">2</span> <span class="n">norm_num</span> </pre></div> </div> <p>You can give the <code class="docutils literal notranslate"><span class="pre">use</span></code> tactic proofs as well as data:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">,</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">h1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="o">(</span><span class="mi">5</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">norm_num</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">h2</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="mi">5</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">norm_num</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="o">,</span><span class="w"> </span><span class="n">h1</span><span class="o">,</span><span class="w"> </span><span class="n">h2</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">x</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">,</span> <span class="mi">2</span> <span class="bp"><</span> <span class="n">x</span> <span class="bp">∧</span> <span class="n">x</span> <span class="bp"><</span> <span class="mi">3</span> <span class="o">:=</span> <span class="kd">by</span> <span class="k">have</span> <span class="n">h1</span> <span class="o">:</span> <span class="mi">2</span> <span class="bp"><</span> <span class="o">(</span><span class="mi">5</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="bp">/</span> <span class="mi">2</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">norm_num</span> <span class="k">have</span> <span class="n">h2</span> <span class="o">:</span> <span class="o">(</span><span class="mi">5</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="bp">/</span> <span class="mi">2</span> <span class="bp"><</span> <span class="mi">3</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">norm_num</span> <span class="n">use</span> <span class="mi">5</span> <span class="bp">/</span> <span class="mi">2</span><span class="o">,</span> <span class="n">h1</span><span class="o">,</span> <span class="n">h2</span> </pre></div> </div> <p>In fact, the <code class="docutils literal notranslate"><span class="pre">use</span></code> tactic automatically tries to use available assumptions as well.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">,</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="o">(</span><span class="mi">5</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="o">(</span><span class="mi">5</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">norm_num</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">x</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">,</span> <span class="mi">2</span> <span class="bp"><</span> <span class="n">x</span> <span class="bp">∧</span> <span class="n">x</span> <span class="bp"><</span> <span class="mi">3</span> <span class="o">:=</span> <span class="kd">by</span> <span class="k">have</span> <span class="n">h</span> <span class="o">:</span> <span class="mi">2</span> <span class="bp"><</span> <span class="o">(</span><span class="mi">5</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="bp">/</span> <span class="mi">2</span> <span class="bp">∧</span> <span class="o">(</span><span class="mi">5</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="bp">/</span> <span class="mi">2</span> <span class="bp"><</span> <span class="mi">3</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">norm_num</span> <span class="n">use</span> <span class="mi">5</span> <span class="bp">/</span> <span class="mi">2</span> </pre></div> </div> <p id="index-7">Alternatively, we can use Lean’s <em>anonymous constructor</em> notation to construct a proof of an existential quantifier.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">,</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="o">(</span><span class="mi">5</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="o">(</span><span class="mi">5</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">norm_num</span> <span class="w"> </span><span class="o">⟨</span><span class="mi">5</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="o">,</span><span class="w"> </span><span class="n">h</span><span class="o">⟩</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">x</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">,</span> <span class="mi">2</span> <span class="bp"><</span> <span class="n">x</span> <span class="bp">∧</span> <span class="n">x</span> <span class="bp"><</span> <span class="mi">3</span> <span class="o">:=</span> <span class="k">have</span> <span class="n">h</span> <span class="o">:</span> <span class="mi">2</span> <span class="bp"><</span> <span class="o">(</span><span class="mi">5</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="bp">/</span> <span class="mi">2</span> <span class="bp">∧</span> <span class="o">(</span><span class="mi">5</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="bp">/</span> <span class="mi">2</span> <span class="bp"><</span> <span class="mi">3</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">norm_num</span> <span class="o">⟨</span><span class="mi">5</span> <span class="bp">/</span> <span class="mi">2</span><span class="o">,</span> <span class="n">h</span><span class="o">⟩</span> </pre></div> </div> <p>Notice that there is no <code class="docutils literal notranslate"><span class="pre">by</span></code>; here we are giving an explicit proof term.
-
@@ -545,8 +541,8 @@ tell Lean to put together the given data usingwhatever construction is appropriate for the current goal. We can use the notation without going first into tactic mode:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">,</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">⟨</span><span class="mi">5</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="o">,</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">norm_num</span><span class="o">⟩</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">x</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">,</span> <span class="mi">2</span> <span class="bp"><</span> <span class="n">x</span> <span class="bp">∧</span> <span class="n">x</span> <span class="bp"><</span> <span class="mi">3</span> <span class="o">:=</span> <span class="o">⟨</span><span class="mi">5</span> <span class="bp">/</span> <span class="mi">2</span><span class="o">,</span> <span class="kd">by</span> <span class="n">norm_num</span><span class="o">⟩</span> </pre></div> </div> <p>So now we know how to <em>prove</em> an exists statement.
-
@@ -560,29 +556,29 @@ which say that <code class="docutils literal notranslate"><span class="pre">a</srespectively. We can use the existential quantifier to say that “<code class="docutils literal notranslate"><span class="pre">f</span></code> is bounded” without specifying the bound:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">FnUb</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Prop</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">a</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">FnUb</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="kt">Prop</span> <span class="o">:=</span> <span class="bp">∀</span> <span class="n">x</span><span class="o">,</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">a</span> <span class="kd">def</span><span class="w"> </span><span class="n">FnLb</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Prop</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span> <span class="kd">def</span> <span class="n">FnLb</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="kt">Prop</span> <span class="o">:=</span> <span class="bp">∀</span> <span class="n">x</span><span class="o">,</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">f</span> <span class="n">x</span> <span class="kd">def</span><span class="w"> </span><span class="n">FnHasUb</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="n">FnUb</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">a</span> <span class="kd">def</span> <span class="n">FnHasUb</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:=</span> <span class="bp">∃</span> <span class="n">a</span><span class="o">,</span> <span class="n">FnUb</span> <span class="n">f</span> <span class="n">a</span> <span class="kd">def</span><span class="w"> </span><span class="n">FnHasLb</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="n">FnLb</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">a</span> <span class="kd">def</span> <span class="n">FnHasLb</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:=</span> <span class="bp">∃</span> <span class="n">a</span><span class="o">,</span> <span class="n">FnLb</span> <span class="n">f</span> <span class="n">a</span> </pre></div> </div> <p>We can use the theorem <code class="docutils literal notranslate"><span class="pre">FnUb_add</span></code> from the last section to prove that if <code class="docutils literal notranslate"><span class="pre">f</span></code> and <code class="docutils literal notranslate"><span class="pre">g</span></code> have upper bounds, then so does <code class="docutils literal notranslate"><span class="pre">fun</span> <span class="pre">x</span> <span class="pre">↦</span> <span class="pre">f</span> <span class="pre">x</span> <span class="pre">+</span> <span class="pre">g</span> <span class="pre">x</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">f</span> <span class="n">g</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">}</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">ubf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnHasUb</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">ubg</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnHasUb</span><span class="w"> </span><span class="n">g</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnHasUb</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">ubf</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="n">ubfa</span><span class="o">⟩</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">ubg</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">b</span><span class="o">,</span><span class="w"> </span><span class="n">ubgb</span><span class="o">⟩</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">fnUb_add</span><span class="w"> </span><span class="n">ubfa</span><span class="w"> </span><span class="n">ubgb</span> <span class="kd">example</span> <span class="o">(</span><span class="n">ubf</span> <span class="o">:</span> <span class="n">FnHasUb</span> <span class="n">f</span><span class="o">)</span> <span class="o">(</span><span class="n">ubg</span> <span class="o">:</span> <span class="n">FnHasUb</span> <span class="n">g</span><span class="o">)</span> <span class="o">:</span> <span class="n">FnHasUb</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">g</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rcases</span> <span class="n">ubf</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">a</span><span class="o">,</span> <span class="n">ubfa</span><span class="o">⟩</span> <span class="n">rcases</span> <span class="n">ubg</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">b</span><span class="o">,</span> <span class="n">ubgb</span><span class="o">⟩</span> <span class="n">use</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">b</span> <span class="n">apply</span> <span class="n">fnUb_add</span> <span class="n">ubfa</span> <span class="n">ubgb</span> </pre></div> </div> <p id="index-8">The <code class="docutils literal notranslate"><span class="pre">rcases</span></code> tactic unpacks the information
-
@@ -610,35 +606,35 @@ from the last section into named theorems,as we did with <code class="docutils literal notranslate"><span class="pre">fn_ub_add</span></code>, or you can insert the arguments directly into the proofs.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">lbf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnHasLb</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">lbg</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnHasLb</span><span class="w"> </span><span class="n">g</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnHasLb</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">lbf</span> <span class="o">:</span> <span class="n">FnHasLb</span> <span class="n">f</span><span class="o">)</span> <span class="o">(</span><span class="n">lbg</span> <span class="o">:</span> <span class="n">FnHasLb</span> <span class="n">g</span><span class="o">)</span> <span class="o">:</span> <span class="n">FnHasLb</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">g</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">ubf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnHasUb</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">≥</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnHasUb</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">{</span><span class="n">c</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">ubf</span> <span class="o">:</span> <span class="n">FnHasUb</span> <span class="n">f</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">c</span> <span class="bp">≥</span> <span class="mi">0</span><span class="o">)</span> <span class="o">:</span> <span class="n">FnHasUb</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">c</span> <span class="bp">*</span> <span class="n">f</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p id="index-9">The “r” in <code class="docutils literal notranslate"><span class="pre">rcases</span></code> stands for “recursive,” because it allows us to use arbitrarily complex patterns to unpack nested data. The <code class="docutils literal notranslate"><span class="pre">rintro</span></code> tactic is a combination of <code class="docutils literal notranslate"><span class="pre">intro</span></code> and <code class="docutils literal notranslate"><span class="pre">rcases</span></code>:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnHasUb</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">FnHasUb</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">FnHasUb</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rintro</span><span class="w"> </span><span class="o">⟨</span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="n">ubfa</span><span class="o">⟩</span><span class="w"> </span><span class="o">⟨</span><span class="n">b</span><span class="o">,</span><span class="w"> </span><span class="n">ubgb</span><span class="o">⟩</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="o">⟨</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">,</span><span class="w"> </span><span class="n">fnUb_add</span><span class="w"> </span><span class="n">ubfa</span><span class="w"> </span><span class="n">ubgb</span><span class="o">⟩</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">FnHasUb</span> <span class="n">f</span> <span class="bp">→</span> <span class="n">FnHasUb</span> <span class="n">g</span> <span class="bp">→</span> <span class="n">FnHasUb</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">g</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rintro</span> <span class="o">⟨</span><span class="n">a</span><span class="o">,</span> <span class="n">ubfa</span><span class="o">⟩</span> <span class="o">⟨</span><span class="n">b</span><span class="o">,</span> <span class="n">ubgb</span><span class="o">⟩</span> <span class="n">exact</span> <span class="o">⟨</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">,</span> <span class="n">fnUb_add</span> <span class="n">ubfa</span> <span class="n">ubgb</span><span class="o">⟩</span> </pre></div> </div> <p>In fact, Lean also supports a pattern-matching fun in expressions and proof terms:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnHasUb</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">FnHasUb</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">FnHasUb</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="o">⟨</span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="n">ubfa</span><span class="o">⟩</span><span class="w"> </span><span class="o">⟨</span><span class="n">b</span><span class="o">,</span><span class="w"> </span><span class="n">ubgb</span><span class="o">⟩</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="o">⟨</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">,</span><span class="w"> </span><span class="n">fnUb_add</span><span class="w"> </span><span class="n">ubfa</span><span class="w"> </span><span class="n">ubgb</span><span class="o">⟩</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">FnHasUb</span> <span class="n">f</span> <span class="bp">→</span> <span class="n">FnHasUb</span> <span class="n">g</span> <span class="bp">→</span> <span class="n">FnHasUb</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">g</span> <span class="n">x</span> <span class="o">:=</span> <span class="k">fun</span> <span class="o">⟨</span><span class="n">a</span><span class="o">,</span> <span class="n">ubfa</span><span class="o">⟩</span> <span class="o">⟨</span><span class="n">b</span><span class="o">,</span> <span class="n">ubgb</span><span class="o">⟩</span> <span class="bp">↦</span> <span class="o">⟨</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">,</span> <span class="n">fnUb_add</span> <span class="n">ubfa</span> <span class="n">ubgb</span><span class="o">⟩</span> </pre></div> </div> <p>The task of unpacking information in a hypothesis is so important that Lean and Mathlib provide a number of ways to do it. For example, the <code class="docutils literal notranslate"><span class="pre">obtain</span></code> tactic provides suggestive syntax:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">ubf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnHasUb</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">ubg</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnHasUb</span><span class="w"> </span><span class="n">g</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnHasUb</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">obtain</span><span class="w"> </span><span class="o">⟨</span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="n">ubfa</span><span class="o">⟩</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">ubf</span> <span class="w"> </span><span class="n">obtain</span><span class="w"> </span><span class="o">⟨</span><span class="n">b</span><span class="o">,</span><span class="w"> </span><span class="n">ubgb</span><span class="o">⟩</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">ubg</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="o">⟨</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">,</span><span class="w"> </span><span class="n">fnUb_add</span><span class="w"> </span><span class="n">ubfa</span><span class="w"> </span><span class="n">ubgb</span><span class="o">⟩</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">ubf</span> <span class="o">:</span> <span class="n">FnHasUb</span> <span class="n">f</span><span class="o">)</span> <span class="o">(</span><span class="n">ubg</span> <span class="o">:</span> <span class="n">FnHasUb</span> <span class="n">g</span><span class="o">)</span> <span class="o">:</span> <span class="n">FnHasUb</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">g</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">obtain</span> <span class="o">⟨</span><span class="n">a</span><span class="o">,</span> <span class="n">ubfa</span><span class="o">⟩</span> <span class="o">:=</span> <span class="n">ubf</span> <span class="n">obtain</span> <span class="o">⟨</span><span class="n">b</span><span class="o">,</span> <span class="n">ubgb</span><span class="o">⟩</span> <span class="o">:=</span> <span class="n">ubg</span> <span class="n">exact</span> <span class="o">⟨</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">,</span> <span class="n">fnUb_add</span> <span class="n">ubfa</span> <span class="n">ubgb</span><span class="o">⟩</span> </pre></div> </div> <p>Think of the first <code class="docutils literal notranslate"><span class="pre">obtain</span></code> instruction as matching the “contents” of <code class="docutils literal notranslate"><span class="pre">ubf</span></code>
-
@@ -648,29 +644,29 @@ there is a small difference in that <code class="docutils literal notranslate"><when it is done, whereas it is still present after <code class="docutils literal notranslate"><span class="pre">obtain</span></code>.</p> <p>Lean also supports syntax that is similar to that used in other functional programming languages:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">ubf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnHasUb</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">ubg</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnHasUb</span><span class="w"> </span><span class="n">g</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnHasUb</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">cases</span><span class="w"> </span><span class="n">ubf</span> <span class="w"> </span><span class="n">case</span><span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">ubfa</span><span class="w"> </span><span class="bp">=></span> <span class="w"> </span><span class="n">cases</span><span class="w"> </span><span class="n">ubg</span> <span class="w"> </span><span class="n">case</span><span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">ubgb</span><span class="w"> </span><span class="bp">=></span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="o">⟨</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">,</span><span class="w"> </span><span class="n">fnUb_add</span><span class="w"> </span><span class="n">ubfa</span><span class="w"> </span><span class="n">ubgb</span><span class="o">⟩</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">ubf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnHasUb</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">ubg</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnHasUb</span><span class="w"> </span><span class="n">g</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnHasUb</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">cases</span><span class="w"> </span><span class="n">ubf</span> <span class="w"> </span><span class="n">next</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">ubfa</span><span class="w"> </span><span class="bp">=></span> <span class="w"> </span><span class="n">cases</span><span class="w"> </span><span class="n">ubg</span> <span class="w"> </span><span class="n">next</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">ubgb</span><span class="w"> </span><span class="bp">=></span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="o">⟨</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">,</span><span class="w"> </span><span class="n">fnUb_add</span><span class="w"> </span><span class="n">ubfa</span><span class="w"> </span><span class="n">ubgb</span><span class="o">⟩</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">ubf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnHasUb</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">ubg</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnHasUb</span><span class="w"> </span><span class="n">g</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnHasUb</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="k">match</span><span class="w"> </span><span class="n">ubf</span><span class="o">,</span><span class="w"> </span><span class="n">ubg</span><span class="w"> </span><span class="k">with</span> <span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="o">⟨</span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="n">ubfa</span><span class="o">⟩,</span><span class="w"> </span><span class="o">⟨</span><span class="n">b</span><span class="o">,</span><span class="w"> </span><span class="n">ubgb</span><span class="o">⟩</span><span class="w"> </span><span class="bp">=></span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="o">⟨</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">,</span><span class="w"> </span><span class="n">fnUb_add</span><span class="w"> </span><span class="n">ubfa</span><span class="w"> </span><span class="n">ubgb</span><span class="o">⟩</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">ubf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnHasUb</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">ubg</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnHasUb</span><span class="w"> </span><span class="n">g</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnHasUb</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="k">match</span><span class="w"> </span><span class="n">ubf</span><span class="o">,</span><span class="w"> </span><span class="n">ubg</span><span class="w"> </span><span class="k">with</span> <span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="o">⟨</span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="n">ubfa</span><span class="o">⟩,</span><span class="w"> </span><span class="o">⟨</span><span class="n">b</span><span class="o">,</span><span class="w"> </span><span class="n">ubgb</span><span class="o">⟩</span><span class="w"> </span><span class="bp">=></span> <span class="w"> </span><span class="o">⟨</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">,</span><span class="w"> </span><span class="n">fnUb_add</span><span class="w"> </span><span class="n">ubfa</span><span class="w"> </span><span class="n">ubgb</span><span class="o">⟩</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">ubf</span> <span class="o">:</span> <span class="n">FnHasUb</span> <span class="n">f</span><span class="o">)</span> <span class="o">(</span><span class="n">ubg</span> <span class="o">:</span> <span class="n">FnHasUb</span> <span class="n">g</span><span class="o">)</span> <span class="o">:</span> <span class="n">FnHasUb</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">g</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">cases</span> <span class="n">ubf</span> <span class="n">case</span> <span class="n">intro</span> <span class="n">a</span> <span class="n">ubfa</span> <span class="bp">=></span> <span class="n">cases</span> <span class="n">ubg</span> <span class="n">case</span> <span class="n">intro</span> <span class="n">b</span> <span class="n">ubgb</span> <span class="bp">=></span> <span class="n">exact</span> <span class="o">⟨</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">,</span> <span class="n">fnUb_add</span> <span class="n">ubfa</span> <span class="n">ubgb</span><span class="o">⟩</span> <span class="kd">example</span> <span class="o">(</span><span class="n">ubf</span> <span class="o">:</span> <span class="n">FnHasUb</span> <span class="n">f</span><span class="o">)</span> <span class="o">(</span><span class="n">ubg</span> <span class="o">:</span> <span class="n">FnHasUb</span> <span class="n">g</span><span class="o">)</span> <span class="o">:</span> <span class="n">FnHasUb</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">g</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">cases</span> <span class="n">ubf</span> <span class="n">next</span> <span class="n">a</span> <span class="n">ubfa</span> <span class="bp">=></span> <span class="n">cases</span> <span class="n">ubg</span> <span class="n">next</span> <span class="n">b</span> <span class="n">ubgb</span> <span class="bp">=></span> <span class="n">exact</span> <span class="o">⟨</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">,</span> <span class="n">fnUb_add</span> <span class="n">ubfa</span> <span class="n">ubgb</span><span class="o">⟩</span> <span class="kd">example</span> <span class="o">(</span><span class="n">ubf</span> <span class="o">:</span> <span class="n">FnHasUb</span> <span class="n">f</span><span class="o">)</span> <span class="o">(</span><span class="n">ubg</span> <span class="o">:</span> <span class="n">FnHasUb</span> <span class="n">g</span><span class="o">)</span> <span class="o">:</span> <span class="n">FnHasUb</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">g</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="k">match</span> <span class="n">ubf</span><span class="o">,</span> <span class="n">ubg</span> <span class="k">with</span> <span class="bp">|</span> <span class="o">⟨</span><span class="n">a</span><span class="o">,</span> <span class="n">ubfa</span><span class="o">⟩,</span> <span class="o">⟨</span><span class="n">b</span><span class="o">,</span> <span class="n">ubgb</span><span class="o">⟩</span> <span class="bp">=></span> <span class="n">exact</span> <span class="o">⟨</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">,</span> <span class="n">fnUb_add</span> <span class="n">ubfa</span> <span class="n">ubgb</span><span class="o">⟩</span> <span class="kd">example</span> <span class="o">(</span><span class="n">ubf</span> <span class="o">:</span> <span class="n">FnHasUb</span> <span class="n">f</span><span class="o">)</span> <span class="o">(</span><span class="n">ubg</span> <span class="o">:</span> <span class="n">FnHasUb</span> <span class="n">g</span><span class="o">)</span> <span class="o">:</span> <span class="n">FnHasUb</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">g</span> <span class="n">x</span> <span class="o">:=</span> <span class="k">match</span> <span class="n">ubf</span><span class="o">,</span> <span class="n">ubg</span> <span class="k">with</span> <span class="bp">|</span> <span class="o">⟨</span><span class="n">a</span><span class="o">,</span> <span class="n">ubfa</span><span class="o">⟩,</span> <span class="o">⟨</span><span class="n">b</span><span class="o">,</span> <span class="n">ubgb</span><span class="o">⟩</span> <span class="bp">=></span> <span class="o">⟨</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">,</span> <span class="n">fnUb_add</span> <span class="n">ubfa</span> <span class="n">ubgb</span><span class="o">⟩</span> </pre></div> </div> <p>In the first example, if you put your cursor after <code class="docutils literal notranslate"><span class="pre">cases</span> <span class="pre">ubf</span></code>,
-
@@ -700,18 +696,18 @@ quantifiers at once.We then provide the magic values needed to express <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">*</span> <span class="pre">y</span></code> as a sum of squares as a list to the <code class="docutils literal notranslate"><span class="pre">use</span></code> statement, and we use <code class="docutils literal notranslate"><span class="pre">ring</span></code> to verify that they work.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">CommRing</span><span class="w"> </span><span class="n">α</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">CommRing</span> <span class="n">α</span><span class="o">]</span> <span class="kd">def</span><span class="w"> </span><span class="n">SumOfSquares</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="o">,</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span> <span class="kd">def</span> <span class="n">SumOfSquares</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">α</span><span class="o">)</span> <span class="o">:=</span> <span class="bp">∃</span> <span class="n">a</span> <span class="n">b</span><span class="o">,</span> <span class="n">x</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">^</span> <span class="mi">2</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">sumOfSquares_mul</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">sosx</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">SumOfSquares</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">sosy</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">SumOfSquares</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">SumOfSquares</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">sosx</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="n">b</span><span class="o">,</span><span class="w"> </span><span class="n">xeq</span><span class="o">⟩</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">sosy</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">c</span><span class="o">,</span><span class="w"> </span><span class="n">d</span><span class="o">,</span><span class="w"> </span><span class="n">yeq</span><span class="o">⟩</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">xeq</span><span class="o">,</span><span class="w"> </span><span class="n">yeq</span><span class="o">]</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">d</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span> <span class="w"> </span><span class="n">ring</span> <span class="kd">theorem</span> <span class="n">sumOfSquares_mul</span> <span class="o">{</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">α</span><span class="o">}</span> <span class="o">(</span><span class="n">sosx</span> <span class="o">:</span> <span class="n">SumOfSquares</span> <span class="n">x</span><span class="o">)</span> <span class="o">(</span><span class="n">sosy</span> <span class="o">:</span> <span class="n">SumOfSquares</span> <span class="n">y</span><span class="o">)</span> <span class="o">:</span> <span class="n">SumOfSquares</span> <span class="o">(</span><span class="n">x</span> <span class="bp">*</span> <span class="n">y</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rcases</span> <span class="n">sosx</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">a</span><span class="o">,</span> <span class="n">b</span><span class="o">,</span> <span class="n">xeq</span><span class="o">⟩</span> <span class="n">rcases</span> <span class="n">sosy</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">c</span><span class="o">,</span> <span class="n">d</span><span class="o">,</span> <span class="n">yeq</span><span class="o">⟩</span> <span class="n">rw</span> <span class="o">[</span><span class="n">xeq</span><span class="o">,</span> <span class="n">yeq</span><span class="o">]</span> <span class="n">use</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">c</span> <span class="bp">-</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">d</span><span class="o">,</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">d</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">c</span> <span class="n">ring</span> </pre></div> </div> <p>This proof doesn’t provide much insight,
-
@@ -741,23 +737,23 @@ an abbreviation:if you use the keyword <code class="docutils literal notranslate"><span class="pre">rfl</span></code> in place of a new identifier, <code class="docutils literal notranslate"><span class="pre">rcases</span></code> does the rewriting automatically (this trick doesn’t work with pattern-matching lambdas).</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">sumOfSquares_mul'</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">sosx</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">SumOfSquares</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">sosy</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">SumOfSquares</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">SumOfSquares</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">sosx</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="n">b</span><span class="o">,</span><span class="w"> </span><span class="n">rfl</span><span class="o">⟩</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">sosy</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">c</span><span class="o">,</span><span class="w"> </span><span class="n">d</span><span class="o">,</span><span class="w"> </span><span class="n">rfl</span><span class="o">⟩</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">d</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span> <span class="w"> </span><span class="n">ring</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">sumOfSquares_mul'</span> <span class="o">{</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">α</span><span class="o">}</span> <span class="o">(</span><span class="n">sosx</span> <span class="o">:</span> <span class="n">SumOfSquares</span> <span class="n">x</span><span class="o">)</span> <span class="o">(</span><span class="n">sosy</span> <span class="o">:</span> <span class="n">SumOfSquares</span> <span class="n">y</span><span class="o">)</span> <span class="o">:</span> <span class="n">SumOfSquares</span> <span class="o">(</span><span class="n">x</span> <span class="bp">*</span> <span class="n">y</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rcases</span> <span class="n">sosx</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">a</span><span class="o">,</span> <span class="n">b</span><span class="o">,</span> <span class="n">rfl</span><span class="o">⟩</span> <span class="n">rcases</span> <span class="n">sosy</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">c</span><span class="o">,</span> <span class="n">d</span><span class="o">,</span> <span class="n">rfl</span><span class="o">⟩</span> <span class="n">use</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">c</span> <span class="bp">-</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">d</span><span class="o">,</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">d</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">c</span> <span class="n">ring</span> </pre></div> </div> <p>As with the universal quantifier, you can find existential quantifiers hidden all over if you know how to spot them. For example, divisibility is implicitly an “exists” statement.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">divab</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">divbc</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">c</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">divab</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">d</span><span class="o">,</span><span class="w"> </span><span class="n">beq</span><span class="o">⟩</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">divbc</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">e</span><span class="o">,</span><span class="w"> </span><span class="n">ceq</span><span class="o">⟩</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">ceq</span><span class="o">,</span><span class="w"> </span><span class="n">beq</span><span class="o">]</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">e</span><span class="bp">;</span><span class="w"> </span><span class="n">ring</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">divab</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">∣</span> <span class="n">b</span><span class="o">)</span> <span class="o">(</span><span class="n">divbc</span> <span class="o">:</span> <span class="n">b</span> <span class="bp">∣</span> <span class="n">c</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">∣</span> <span class="n">c</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rcases</span> <span class="n">divab</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">d</span><span class="o">,</span> <span class="n">beq</span><span class="o">⟩</span> <span class="n">rcases</span> <span class="n">divbc</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">e</span><span class="o">,</span> <span class="n">ceq</span><span class="o">⟩</span> <span class="n">rw</span> <span class="o">[</span><span class="n">ceq</span><span class="o">,</span> <span class="n">beq</span><span class="o">]</span> <span class="n">use</span> <span class="n">d</span> <span class="bp">*</span> <span class="n">e</span><span class="bp">;</span> <span class="n">ring</span> </pre></div> </div> <p>And once again, this provides a nice setting for using
-
@@ -765,8 +761,8 @@ For example, divisibility is implicitly an “exists” statement.</p>Try it out in the proof above. It feels pretty good!</p> <p>Then try proving the following:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">divab</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">divac</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">c</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">divab</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">∣</span> <span class="n">b</span><span class="o">)</span> <span class="o">(</span><span class="n">divac</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">∣</span> <span class="n">c</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">∣</span> <span class="n">b</span> <span class="bp">+</span> <span class="n">c</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p id="index-10">For another important example, a function <span class="math notranslate nohighlight">\(f : \alpha \to \beta\)</span>
-
@@ -777,48 +773,48 @@ such that <span class="math notranslate nohighlight">\(f(x) = y\)</span>.Notice that this statement includes both a universal and an existential quantifier, which explains why the next example makes use of both <code class="docutils literal notranslate"><span class="pre">intro</span></code> and <code class="docutils literal notranslate"><span class="pre">use</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Surjective</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">x</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">c</span> <span class="w"> </span><span class="n">dsimp</span><span class="bp">;</span><span class="w"> </span><span class="n">ring</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">c</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">:</span> <span class="n">Surjective</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">c</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">x</span> <span class="n">use</span> <span class="n">x</span> <span class="bp">-</span> <span class="n">c</span> <span class="n">dsimp</span><span class="bp">;</span> <span class="n">ring</span> </pre></div> </div> <p>Try this example yourself using the theorem <code class="docutils literal notranslate"><span class="pre">mul_div_cancel₀</span></code>.:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Surjective</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">c</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">c</span> <span class="bp">≠</span> <span class="mi">0</span><span class="o">)</span> <span class="o">:</span> <span class="n">Surjective</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">c</span> <span class="bp">*</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p id="index-11">At this point, it is worth mentioning that there is a tactic, <code class="docutils literal notranslate"><span class="pre">field_simp</span></code>, that will often clear denominators in a useful way. It can be used in conjunction with the <code class="docutils literal notranslate"><span class="pre">ring</span></code> tactic.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">field_simp</span><span class="w"> </span><span class="o">[</span><span class="n">h</span><span class="o">]</span> <span class="w"> </span><span class="n">ring</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">-</span> <span class="n">y</span> <span class="bp">≠</span> <span class="mi">0</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">x</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">-</span> <span class="n">y</span> <span class="bp">^</span> <span class="mi">2</span><span class="o">)</span> <span class="bp">/</span> <span class="o">(</span><span class="n">x</span> <span class="bp">-</span> <span class="n">y</span><span class="o">)</span> <span class="bp">=</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">y</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">field_simp</span> <span class="o">[</span><span class="n">h</span><span class="o">]</span> <span class="n">ring</span> </pre></div> </div> <p>The next example uses a surjectivity hypothesis by applying it to a suitable value. Note that you can use <code class="docutils literal notranslate"><span class="pre">rcases</span></code> with any expression, not just a hypothesis.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Surjective</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">hx</span><span class="o">⟩</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">x</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">hx</span><span class="o">]</span> <span class="w"> </span><span class="n">norm_num</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">Surjective</span> <span class="n">f</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">x</span><span class="o">,</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">=</span> <span class="mi">4</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rcases</span> <span class="n">h</span> <span class="mi">2</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">x</span><span class="o">,</span> <span class="n">hx</span><span class="o">⟩</span> <span class="n">use</span> <span class="n">x</span> <span class="n">rw</span> <span class="o">[</span><span class="n">hx</span><span class="o">]</span> <span class="n">norm_num</span> </pre></div> </div> <p>See if you can use these methods to show that the composition of surjective functions is surjective.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">β</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">γ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">g</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">β</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">γ</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">β</span><span class="o">}</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">{</span><span class="n">β</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">{</span><span class="n">γ</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="kd">variable</span> <span class="o">{</span><span class="n">g</span> <span class="o">:</span> <span class="n">β</span> <span class="bp">→</span> <span class="n">γ</span><span class="o">}</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">β</span><span class="o">}</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">surjg</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Surjective</span><span class="w"> </span><span class="n">g</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">surjf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Surjective</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Surjective</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">surjg</span> <span class="o">:</span> <span class="n">Surjective</span> <span class="n">g</span><span class="o">)</span> <span class="o">(</span><span class="n">surjf</span> <span class="o">:</span> <span class="n">Surjective</span> <span class="n">f</span><span class="o">)</span> <span class="o">:</span> <span class="n">Surjective</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">g</span> <span class="o">(</span><span class="n">f</span> <span class="n">x</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> </section> <section id="negation"> <span id="id4"></span><h2><span class="section-number">3.3. </span>Negation<a class="headerlink" href="#negation" title="Link to this heading"></a></h2> <span id="id4"></span><h2><span class="section-number">3.3. </span>Negation<a class="headerlink" href="#negation" title="Permalink to this heading"></a></h2> <p>The symbol <code class="docutils literal notranslate"><span class="pre">¬</span></code> is meant to express negation, so <code class="docutils literal notranslate"><span class="pre">¬</span> <span class="pre">x</span> <span class="pre"><</span> <span class="pre">y</span></code> says that <code class="docutils literal notranslate"><span class="pre">x</span></code> is not less than <code class="docutils literal notranslate"><span class="pre">y</span></code>, <code class="docutils literal notranslate"><span class="pre">¬</span> <span class="pre">x</span> <span class="pre">=</span> <span class="pre">y</span></code> (or, equivalently, <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">≠</span> <span class="pre">y</span></code>) says that
-
@@ -839,10 +835,10 @@ which says that we have <code class="docutils literal notranslate"><span class="The asymmetry principle <code class="docutils literal notranslate"><span class="pre">lt_asymm</span></code> says that we have <code class="docutils literal notranslate"><span class="pre">a</span> <span class="pre"><</span> <span class="pre">b</span> <span class="pre">→</span> <span class="pre">¬</span> <span class="pre">b</span> <span class="pre"><</span> <span class="pre">a</span></code>. Let’s show that <code class="docutils literal notranslate"><span class="pre">lt_asymm</span></code> follows from <code class="docutils literal notranslate"><span class="pre">lt_irrefl</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬</span><span class="n">b</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">h'</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">lt_trans</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="n">h'</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">lt_irrefl</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">this</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">a</span> <span class="bp"><</span> <span class="n">b</span><span class="o">)</span> <span class="o">:</span> <span class="bp">¬</span><span class="n">b</span> <span class="bp"><</span> <span class="n">a</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">h'</span> <span class="k">have</span> <span class="o">:</span> <span class="n">a</span> <span class="bp"><</span> <span class="n">a</span> <span class="o">:=</span> <span class="n">lt_trans</span> <span class="n">h</span> <span class="n">h'</span> <span class="n">apply</span> <span class="n">lt_irrefl</span> <span class="n">a</span> <span class="n">this</span> </pre></div> </div> <p id="index-12">This example introduces a couple of new tricks.
-
@@ -859,41 +855,41 @@ by applying <code class="docutils literal notranslate"><span class="pre">lt_irre<p>Here is another example, which uses the predicate <code class="docutils literal notranslate"><span class="pre">FnHasUb</span></code> defined in the last section, which says that a function has an upper bound.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬</span><span class="n">FnHasUb</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">fnub</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">fnub</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="n">fnuba</span><span class="o">⟩</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">hx</span><span class="o">⟩</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">fnuba</span><span class="w"> </span><span class="n">x</span> <span class="w"> </span><span class="n">linarith</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span><span class="o">,</span> <span class="bp">∃</span> <span class="n">x</span><span class="o">,</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">></span> <span class="n">a</span><span class="o">)</span> <span class="o">:</span> <span class="bp">¬</span><span class="n">FnHasUb</span> <span class="n">f</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">fnub</span> <span class="n">rcases</span> <span class="n">fnub</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">a</span><span class="o">,</span> <span class="n">fnuba</span><span class="o">⟩</span> <span class="n">rcases</span> <span class="n">h</span> <span class="n">a</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">x</span><span class="o">,</span> <span class="n">hx</span><span class="o">⟩</span> <span class="k">have</span> <span class="o">:</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">a</span> <span class="o">:=</span> <span class="n">fnuba</span> <span class="n">x</span> <span class="n">linarith</span> </pre></div> </div> <p>Remember that it is often convenient to use <code class="docutils literal notranslate"><span class="pre">linarith</span></code> when a goal follows from linear equations and inequalities that are in the context.</p> <p>See if you can prove these in a similar way:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬</span><span class="n">FnHasLb</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span><span class="o">,</span> <span class="bp">∃</span> <span class="n">x</span><span class="o">,</span> <span class="n">f</span> <span class="n">x</span> <span class="bp"><</span> <span class="n">a</span><span class="o">)</span> <span class="o">:</span> <span class="bp">¬</span><span class="n">FnHasLb</span> <span class="n">f</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬</span><span class="n">FnHasUb</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">:</span> <span class="bp">¬</span><span class="n">FnHasUb</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">x</span> <span class="o">:=</span> <span class="gr">sorry</span> </pre></div> </div> <p>Mathlib offers a number of useful theorems for relating orders and negations:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">not_le_of_gt</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="bp">¬</span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">not_lt_of_ge</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≥</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="bp">¬</span><span class="n">a</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">b</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">lt_of_not_ge</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬</span><span class="n">a</span><span class="w"> </span><span class="bp">≥</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">b</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">le_of_not_gt</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬</span><span class="n">a</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="o">(</span><span class="n">not_le_of_gt</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">></span> <span class="n">b</span> <span class="bp">→</span> <span class="bp">¬</span><span class="n">a</span> <span class="bp">≤</span> <span class="n">b</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">not_lt_of_ge</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">≥</span> <span class="n">b</span> <span class="bp">→</span> <span class="bp">¬</span><span class="n">a</span> <span class="bp"><</span> <span class="n">b</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">lt_of_not_ge</span> <span class="o">:</span> <span class="bp">¬</span><span class="n">a</span> <span class="bp">≥</span> <span class="n">b</span> <span class="bp">→</span> <span class="n">a</span> <span class="bp"><</span> <span class="n">b</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">le_of_not_gt</span> <span class="o">:</span> <span class="bp">¬</span><span class="n">a</span> <span class="bp">></span> <span class="n">b</span> <span class="bp">→</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">b</span><span class="o">)</span> </pre></div> </div> <p>Recall the predicate <code class="docutils literal notranslate"><span class="pre">Monotone</span> <span class="pre">f</span></code>, which says that <code class="docutils literal notranslate"><span class="pre">f</span></code> is nondecreasing. Use some of the theorems just enumerated to prove the following:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Monotone</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">Monotone</span> <span class="n">f</span><span class="o">)</span> <span class="o">(</span><span class="n">h'</span> <span class="o">:</span> <span class="n">f</span> <span class="n">a</span> <span class="bp"><</span> <span class="n">f</span> <span class="n">b</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp"><</span> <span class="n">b</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬</span><span class="n">Monotone</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">b</span><span class="o">)</span> <span class="o">(</span><span class="n">h'</span> <span class="o">:</span> <span class="n">f</span> <span class="n">b</span> <span class="bp"><</span> <span class="n">f</span> <span class="n">a</span><span class="o">)</span> <span class="o">:</span> <span class="bp">¬</span><span class="n">Monotone</span> <span class="n">f</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>We can show that the first example in the last snippet
-
@@ -901,12 +897,12 @@ cannot be proved if we replace <code class="docutils literal notranslate"><spanNotice that we can prove the negation of a universally quantified statement by giving a counterexample. Complete the proof.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬∀</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">},</span><span class="w"> </span><span class="n">Monotone</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="o">},</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="k">let</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="o">(</span><span class="mi">0</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">monof</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Monotone</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">h'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">le_refl</span><span class="w"> </span><span class="n">_</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="bp">¬∀</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">},</span> <span class="n">Monotone</span> <span class="n">f</span> <span class="bp">→</span> <span class="bp">∀</span> <span class="o">{</span><span class="n">a</span> <span class="n">b</span><span class="o">},</span> <span class="n">f</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">f</span> <span class="n">b</span> <span class="bp">→</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">b</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">h</span> <span class="k">let</span> <span class="n">f</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">x</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">↦</span> <span class="o">(</span><span class="mi">0</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="k">have</span> <span class="n">monof</span> <span class="o">:</span> <span class="n">Monotone</span> <span class="n">f</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="k">have</span> <span class="n">h'</span> <span class="o">:</span> <span class="n">f</span> <span class="mi">1</span> <span class="bp">≤</span> <span class="n">f</span> <span class="mi">0</span> <span class="o">:=</span> <span class="n">le_refl</span> <span class="n">_</span> <span class="gr">sorry</span> </pre></div> </div> <p id="index-13">This example introduces the <code class="docutils literal notranslate"><span class="pre">let</span></code> tactic,
-
@@ -918,8 +914,8 @@ Lean will unfold the definition of <code class="docutils literal notranslate"><sIn particular, when we prove <code class="docutils literal notranslate"><span class="pre">f</span> <span class="pre">1</span> <span class="pre">≤</span> <span class="pre">f</span> <span class="pre">0</span></code> with <code class="docutils literal notranslate"><span class="pre">le_refl</span></code>, Lean reduces <code class="docutils literal notranslate"><span class="pre">f</span> <span class="pre">1</span></code> and <code class="docutils literal notranslate"><span class="pre">f</span> <span class="pre">0</span></code> to <code class="docutils literal notranslate"><span class="pre">0</span></code>.</p> <p>Use <code class="docutils literal notranslate"><span class="pre">le_of_not_gt</span></code> to prove the following:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span><span class="o">,</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">ε</span> <span class="bp">></span> <span class="mi">0</span><span class="o">,</span> <span class="n">x</span> <span class="bp"><</span> <span class="n">ε</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="mi">0</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>Implicit in many of the proofs we have just done
-
@@ -932,19 +928,19 @@ is equivalent to saying that something fails to have property <code class="docutIn other words, all four of the following implications are valid (but one of them cannot be proved with what we explained so far):</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">P</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="kt">Prop</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">Q</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Prop</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">(</span><span class="n">P</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="kt">Prop</span><span class="o">)</span> <span class="o">(</span><span class="n">Q</span> <span class="o">:</span> <span class="kt">Prop</span><span class="o">)</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬∃</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="bp">¬</span><span class="n">P</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="bp">¬∃</span> <span class="n">x</span><span class="o">,</span> <span class="n">P</span> <span class="n">x</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span><span class="o">,</span> <span class="bp">¬</span><span class="n">P</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="bp">¬</span><span class="n">P</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬∃</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span><span class="o">,</span> <span class="bp">¬</span><span class="n">P</span> <span class="n">x</span><span class="o">)</span> <span class="o">:</span> <span class="bp">¬∃</span> <span class="n">x</span><span class="o">,</span> <span class="n">P</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬∀</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="bp">¬</span><span class="n">P</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="bp">¬∀</span> <span class="n">x</span><span class="o">,</span> <span class="n">P</span> <span class="n">x</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">x</span><span class="o">,</span> <span class="bp">¬</span><span class="n">P</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="bp">¬</span><span class="n">P</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬∀</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">x</span><span class="o">,</span> <span class="bp">¬</span><span class="n">P</span> <span class="n">x</span><span class="o">)</span> <span class="o">:</span> <span class="bp">¬∀</span> <span class="n">x</span><span class="o">,</span> <span class="n">P</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>The first, second, and fourth are straightforward to
-
@@ -956,13 +952,13 @@ from the fact that its nonexistence is contradictory.This is an instance of <em>classical</em> mathematical reasoning. We can use proof by contradiction to prove the third implication as follows.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬∀</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="bp">¬</span><span class="n">P</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">by_contra</span><span class="w"> </span><span class="n">h'</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">x</span> <span class="w"> </span><span class="k">show</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="n">x</span> <span class="w"> </span><span class="n">by_contra</span><span class="w"> </span><span class="n">h''</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">h'</span><span class="w"> </span><span class="o">⟨</span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">h''</span><span class="o">⟩</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="bp">¬∀</span> <span class="n">x</span><span class="o">,</span> <span class="n">P</span> <span class="n">x</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">x</span><span class="o">,</span> <span class="bp">¬</span><span class="n">P</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">by_contra</span> <span class="n">h'</span> <span class="n">apply</span> <span class="n">h</span> <span class="n">intro</span> <span class="n">x</span> <span class="k">show</span> <span class="n">P</span> <span class="n">x</span> <span class="n">by_contra</span> <span class="n">h''</span> <span class="n">exact</span> <span class="n">h'</span> <span class="o">⟨</span><span class="n">x</span><span class="o">,</span> <span class="n">h''</span><span class="o">⟩</span> </pre></div> </div> <p id="index-14">Make sure you understand how this works.
-
@@ -975,18 +971,18 @@ Confirm that you can prove the forward directionof this equivalence using <code class="docutils literal notranslate"><span class="pre">by_contra</span></code>, while the reverse direction follows from the ordinary rules for negation.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬¬</span><span class="n">Q</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Q</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="bp">¬¬</span><span class="n">Q</span><span class="o">)</span> <span class="o">:</span> <span class="n">Q</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Q</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬¬</span><span class="n">Q</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">Q</span><span class="o">)</span> <span class="o">:</span> <span class="bp">¬¬</span><span class="n">Q</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>Use proof by contradiction to establish the following, which is the converse of one of the implications we proved above. (Hint: use <code class="docutils literal notranslate"><span class="pre">intro</span></code> first.)</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬</span><span class="n">FnHasUb</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="bp">¬</span><span class="n">FnHasUb</span> <span class="n">f</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span><span class="o">,</span> <span class="bp">∃</span> <span class="n">x</span><span class="o">,</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">></span> <span class="n">a</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p id="index-15">It is often tedious to work with compound statements with
-
@@ -997,14 +993,14 @@ has been pushed inward.To facilitate this, Mathlib offers a <code class="docutils literal notranslate"><span class="pre">push_neg</span></code> tactic, which restates the goal in this way. The command <code class="docutils literal notranslate"><span class="pre">push_neg</span> <span class="pre">at</span> <span class="pre">h</span></code> restates the hypothesis <code class="docutils literal notranslate"><span class="pre">h</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬∀</span><span class="w"> </span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FnHasUb</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">push_neg</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">h</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="bp">¬∀</span> <span class="n">a</span><span class="o">,</span> <span class="bp">∃</span> <span class="n">x</span><span class="o">,</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">></span> <span class="n">a</span><span class="o">)</span> <span class="o">:</span> <span class="n">FnHasUb</span> <span class="n">f</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">push_neg</span> <span class="n">at</span> <span class="n">h</span> <span class="n">exact</span> <span class="n">h</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬</span><span class="n">FnHasUb</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">dsimp</span><span class="w"> </span><span class="n">only</span><span class="w"> </span><span class="o">[</span><span class="n">FnHasUb</span><span class="o">,</span><span class="w"> </span><span class="n">FnUb</span><span class="o">]</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="n">push_neg</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">h</span> <span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="bp">¬</span><span class="n">FnHasUb</span> <span class="n">f</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span><span class="o">,</span> <span class="bp">∃</span> <span class="n">x</span><span class="o">,</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">></span> <span class="n">a</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">dsimp</span> <span class="n">only</span> <span class="o">[</span><span class="n">FnHasUb</span><span class="o">,</span> <span class="n">FnUb</span><span class="o">]</span> <span class="n">at</span> <span class="n">h</span> <span class="n">push_neg</span> <span class="n">at</span> <span class="n">h</span> <span class="n">exact</span> <span class="n">h</span> </pre></div> </div> <p>In the second example, we use dsimp to
-
@@ -1019,8 +1015,8 @@ Without even knowing how to use the conjunctionsymbol, you should be able to use <code class="docutils literal notranslate"><span class="pre">push_neg</span></code> to prove the following:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬</span><span class="n">Monotone</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="o">,</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="bp">¬</span><span class="n">Monotone</span> <span class="n">f</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">x</span> <span class="n">y</span><span class="o">,</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">y</span> <span class="bp">∧</span> <span class="n">f</span> <span class="n">y</span> <span class="bp"><</span> <span class="n">f</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p id="index-16">Mathlib also has a tactic, <code class="docutils literal notranslate"><span class="pre">contrapose</span></code>,
-
@@ -1032,14 +1028,14 @@ hypothesis <code class="docutils literal notranslate"><span class="pre">h</span>Using <code class="docutils literal notranslate"><span class="pre">contrapose!</span></code> instead of <code class="docutils literal notranslate"><span class="pre">contrapose</span></code> applies <code class="docutils literal notranslate"><span class="pre">push_neg</span></code> to the goal and the relevant hypothesis as well.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬</span><span class="n">FnHasUb</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">contrapose</span><span class="bp">!</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">h</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="bp">¬</span><span class="n">FnHasUb</span> <span class="n">f</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span><span class="o">,</span> <span class="bp">∃</span> <span class="n">x</span><span class="o">,</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">></span> <span class="n">a</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">contrapose</span><span class="bp">!</span> <span class="n">h</span> <span class="n">exact</span> <span class="n">h</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span><span class="o">,</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">ε</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">contrapose</span><span class="bp">!</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span> <span class="w"> </span><span class="n">constructor</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">linarith</span> <span class="kd">example</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">ε</span> <span class="bp">></span> <span class="mi">0</span><span class="o">,</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">ε</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="mi">0</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">contrapose</span><span class="bp">!</span> <span class="n">h</span> <span class="n">use</span> <span class="n">x</span> <span class="bp">/</span> <span class="mi">2</span> <span class="n">constructor</span> <span class="bp"><;></span> <span class="n">linarith</span> </pre></div> </div> <p>We have not yet explained the <code class="docutils literal notranslate"><span class="pre">constructor</span></code> command
-
@@ -1061,16 +1057,16 @@ establishes the goal so we can move on to the next one.<a class="reference internal" href="#disjunction"><span class="std std-numref">Section 3.5</span></a>.)</p> <p id="index-17">Lean provides a number of ways of closing a goal once a contradiction has been reached.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">37</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">exfalso</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">lt_irrefl</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="n">h</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp"><</span> <span class="mi">0</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">></span> <span class="mi">37</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">exfalso</span> <span class="n">apply</span> <span class="n">lt_irrefl</span> <span class="mi">0</span> <span class="n">h</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">37</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">absurd</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="o">(</span><span class="n">lt_irrefl</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span> <span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp"><</span> <span class="mi">0</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">></span> <span class="mi">37</span> <span class="o">:=</span> <span class="n">absurd</span> <span class="n">h</span> <span class="o">(</span><span class="n">lt_irrefl</span> <span class="mi">0</span><span class="o">)</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">37</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">h'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬</span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">lt_irrefl</span><span class="w"> </span><span class="mi">0</span> <span class="w"> </span><span class="n">contradiction</span> <span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp"><</span> <span class="mi">0</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">></span> <span class="mi">37</span> <span class="o">:=</span> <span class="kd">by</span> <span class="k">have</span> <span class="n">h'</span> <span class="o">:</span> <span class="bp">¬</span><span class="mi">0</span> <span class="bp"><</span> <span class="mi">0</span> <span class="o">:=</span> <span class="n">lt_irrefl</span> <span class="mi">0</span> <span class="n">contradiction</span> </pre></div> </div> <p>The <code class="docutils literal notranslate"><span class="pre">exfalso</span></code> tactic replaces the current goal with
-
@@ -1083,18 +1079,18 @@ such as a pair of the form <code class="docutils literal notranslate"><span clasOf course, in this example, <code class="docutils literal notranslate"><span class="pre">linarith</span></code> also works.</p> </section> <section id="conjunction-and-iff"> <span id="conjunction-and-biimplication"></span><h2><span class="section-number">3.4. </span>Conjunction and Iff<a class="headerlink" href="#conjunction-and-iff" title="Link to this heading"></a></h2> <span id="conjunction-and-biimplication"></span><h2><span class="section-number">3.4. </span>Conjunction and Iff<a class="headerlink" href="#conjunction-and-iff" title="Permalink to this heading"></a></h2> <p id="index-18">You have already seen that the conjunction symbol, <code class="docutils literal notranslate"><span class="pre">∧</span></code>, is used to express “and.” The <code class="docutils literal notranslate"><span class="pre">constructor</span></code> tactic allows you to prove a statement of the form <code class="docutils literal notranslate"><span class="pre">A</span> <span class="pre">∧</span> <span class="pre">B</span></code> by proving <code class="docutils literal notranslate"><span class="pre">A</span></code> and then proving <code class="docutils literal notranslate"><span class="pre">B</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h₀</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h₁</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬</span><span class="n">y</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">constructor</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">assumption</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">h₁</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">h</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">h₀</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">y</span><span class="o">)</span> <span class="o">(</span><span class="n">h₁</span> <span class="o">:</span> <span class="bp">¬</span><span class="n">y</span> <span class="bp">≤</span> <span class="n">x</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">y</span> <span class="bp">∧</span> <span class="n">x</span> <span class="bp">≠</span> <span class="n">y</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">constructor</span> <span class="bp">·</span> <span class="n">assumption</span> <span class="n">intro</span> <span class="n">h</span> <span class="n">apply</span> <span class="n">h₁</span> <span class="n">rw</span> <span class="o">[</span><span class="n">h</span><span class="o">]</span> </pre></div> </div> <p id="index-19">In this example, the <code class="docutils literal notranslate"><span class="pre">assumption</span></code> tactic
-
@@ -1107,14 +1103,14 @@ angle brackets.The first is a slick proof-term version of the previous proof, which drops into tactic mode at the keyword <code class="docutils literal notranslate"><span class="pre">by</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h₀</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h₁</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬</span><span class="n">y</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">⟨</span><span class="n">h₀</span><span class="o">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">h₁</span><span class="w"> </span><span class="o">(</span><span class="kd">by</span><span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">h</span><span class="o">])⟩</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">h₀</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">y</span><span class="o">)</span> <span class="o">(</span><span class="n">h₁</span> <span class="o">:</span> <span class="bp">¬</span><span class="n">y</span> <span class="bp">≤</span> <span class="n">x</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">y</span> <span class="bp">∧</span> <span class="n">x</span> <span class="bp">≠</span> <span class="n">y</span> <span class="o">:=</span> <span class="o">⟨</span><span class="n">h₀</span><span class="o">,</span> <span class="k">fun</span> <span class="n">h</span> <span class="bp">↦</span> <span class="n">h₁</span> <span class="o">(</span><span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">h</span><span class="o">])⟩</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h₀</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h₁</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬</span><span class="n">y</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">contrapose</span><span class="bp">!</span><span class="w"> </span><span class="n">h₁</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">h₁</span><span class="o">]</span> <span class="w"> </span><span class="o">⟨</span><span class="n">h₀</span><span class="o">,</span><span class="w"> </span><span class="n">h</span><span class="o">⟩</span> <span class="kd">example</span> <span class="o">{</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">h₀</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">y</span><span class="o">)</span> <span class="o">(</span><span class="n">h₁</span> <span class="o">:</span> <span class="bp">¬</span><span class="n">y</span> <span class="bp">≤</span> <span class="n">x</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">y</span> <span class="bp">∧</span> <span class="n">x</span> <span class="bp">≠</span> <span class="n">y</span> <span class="o">:=</span> <span class="k">have</span> <span class="n">h</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≠</span> <span class="n">y</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">contrapose</span><span class="bp">!</span> <span class="n">h₁</span> <span class="n">rw</span> <span class="o">[</span><span class="n">h₁</span><span class="o">]</span> <span class="o">⟨</span><span class="n">h₀</span><span class="o">,</span> <span class="n">h</span><span class="o">⟩</span> </pre></div> </div> <p><em>Using</em> a conjunction instead of proving one involves unpacking the proofs of the
-
@@ -1123,46 +1119,46 @@ You can use the <code class="docutils literal notranslate"><span class="pre">rcaas well as <code class="docutils literal notranslate"><span class="pre">rintro</span></code> or a pattern-matching <code class="docutils literal notranslate"><span class="pre">fun</span></code>, all in a manner similar to the way they are used with the existential quantifier.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬</span><span class="n">y</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">h₀</span><span class="o">,</span><span class="w"> </span><span class="n">h₁</span><span class="o">⟩</span> <span class="w"> </span><span class="n">contrapose</span><span class="bp">!</span><span class="w"> </span><span class="n">h₁</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">le_antisymm</span><span class="w"> </span><span class="n">h₀</span><span class="w"> </span><span class="n">h₁</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">y</span> <span class="bp">∧</span> <span class="n">x</span> <span class="bp">≠</span> <span class="n">y</span><span class="o">)</span> <span class="o">:</span> <span class="bp">¬</span><span class="n">y</span> <span class="bp">≤</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rcases</span> <span class="n">h</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">h₀</span><span class="o">,</span> <span class="n">h₁</span><span class="o">⟩</span> <span class="n">contrapose</span><span class="bp">!</span> <span class="n">h₁</span> <span class="n">exact</span> <span class="n">le_antisymm</span> <span class="n">h₀</span> <span class="n">h₁</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="bp">¬</span><span class="n">y</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rintro</span><span class="w"> </span><span class="o">⟨</span><span class="n">h₀</span><span class="o">,</span><span class="w"> </span><span class="n">h₁</span><span class="o">⟩</span><span class="w"> </span><span class="n">h'</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">h₁</span><span class="w"> </span><span class="o">(</span><span class="n">le_antisymm</span><span class="w"> </span><span class="n">h₀</span><span class="w"> </span><span class="n">h'</span><span class="o">)</span> <span class="kd">example</span> <span class="o">{</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">y</span> <span class="bp">∧</span> <span class="n">x</span> <span class="bp">≠</span> <span class="n">y</span> <span class="bp">→</span> <span class="bp">¬</span><span class="n">y</span> <span class="bp">≤</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rintro</span> <span class="o">⟨</span><span class="n">h₀</span><span class="o">,</span> <span class="n">h₁</span><span class="o">⟩</span> <span class="n">h'</span> <span class="n">exact</span> <span class="n">h₁</span> <span class="o">(</span><span class="n">le_antisymm</span> <span class="n">h₀</span> <span class="n">h'</span><span class="o">)</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="bp">¬</span><span class="n">y</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="o">⟨</span><span class="n">h₀</span><span class="o">,</span><span class="w"> </span><span class="n">h₁</span><span class="o">⟩</span><span class="w"> </span><span class="n">h'</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">h₁</span><span class="w"> </span><span class="o">(</span><span class="n">le_antisymm</span><span class="w"> </span><span class="n">h₀</span><span class="w"> </span><span class="n">h'</span><span class="o">)</span> <span class="kd">example</span> <span class="o">{</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">y</span> <span class="bp">∧</span> <span class="n">x</span> <span class="bp">≠</span> <span class="n">y</span> <span class="bp">→</span> <span class="bp">¬</span><span class="n">y</span> <span class="bp">≤</span> <span class="n">x</span> <span class="o">:=</span> <span class="k">fun</span> <span class="o">⟨</span><span class="n">h₀</span><span class="o">,</span> <span class="n">h₁</span><span class="o">⟩</span> <span class="n">h'</span> <span class="bp">↦</span> <span class="n">h₁</span> <span class="o">(</span><span class="n">le_antisymm</span> <span class="n">h₀</span> <span class="n">h'</span><span class="o">)</span> </pre></div> </div> <p>In analogy to the <code class="docutils literal notranslate"><span class="pre">obtain</span></code> tactic, there is also a pattern-matching <code class="docutils literal notranslate"><span class="pre">have</span></code>:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬</span><span class="n">y</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">⟨</span><span class="n">h₀</span><span class="o">,</span><span class="w"> </span><span class="n">h₁</span><span class="o">⟩</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="n">contrapose</span><span class="bp">!</span><span class="w"> </span><span class="n">h₁</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">le_antisymm</span><span class="w"> </span><span class="n">h₀</span><span class="w"> </span><span class="n">h₁</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">y</span> <span class="bp">∧</span> <span class="n">x</span> <span class="bp">≠</span> <span class="n">y</span><span class="o">)</span> <span class="o">:</span> <span class="bp">¬</span><span class="n">y</span> <span class="bp">≤</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="k">have</span> <span class="o">⟨</span><span class="n">h₀</span><span class="o">,</span> <span class="n">h₁</span><span class="o">⟩</span> <span class="o">:=</span> <span class="n">h</span> <span class="n">contrapose</span><span class="bp">!</span> <span class="n">h₁</span> <span class="n">exact</span> <span class="n">le_antisymm</span> <span class="n">h₀</span> <span class="n">h₁</span> </pre></div> </div> <p>In contrast to <code class="docutils literal notranslate"><span class="pre">rcases</span></code>, here the <code class="docutils literal notranslate"><span class="pre">have</span></code> tactic leaves <code class="docutils literal notranslate"><span class="pre">h</span></code> in the context. And even though we won’t use them, once again we have the computer scientists’ pattern-matching syntax:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬</span><span class="n">y</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">cases</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="n">case</span><span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">h₀</span><span class="w"> </span><span class="n">h₁</span><span class="w"> </span><span class="bp">=></span> <span class="w"> </span><span class="n">contrapose</span><span class="bp">!</span><span class="w"> </span><span class="n">h₁</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">le_antisymm</span><span class="w"> </span><span class="n">h₀</span><span class="w"> </span><span class="n">h₁</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">y</span> <span class="bp">∧</span> <span class="n">x</span> <span class="bp">≠</span> <span class="n">y</span><span class="o">)</span> <span class="o">:</span> <span class="bp">¬</span><span class="n">y</span> <span class="bp">≤</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">cases</span> <span class="n">h</span> <span class="n">case</span> <span class="n">intro</span> <span class="n">h₀</span> <span class="n">h₁</span> <span class="bp">=></span> <span class="n">contrapose</span><span class="bp">!</span> <span class="n">h₁</span> <span class="n">exact</span> <span class="n">le_antisymm</span> <span class="n">h₀</span> <span class="n">h₁</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬</span><span class="n">y</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">cases</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="n">next</span><span class="w"> </span><span class="n">h₀</span><span class="w"> </span><span class="n">h₁</span><span class="w"> </span><span class="bp">=></span> <span class="w"> </span><span class="n">contrapose</span><span class="bp">!</span><span class="w"> </span><span class="n">h₁</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">le_antisymm</span><span class="w"> </span><span class="n">h₀</span><span class="w"> </span><span class="n">h₁</span> <span class="kd">example</span> <span class="o">{</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">y</span> <span class="bp">∧</span> <span class="n">x</span> <span class="bp">≠</span> <span class="n">y</span><span class="o">)</span> <span class="o">:</span> <span class="bp">¬</span><span class="n">y</span> <span class="bp">≤</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">cases</span> <span class="n">h</span> <span class="n">next</span> <span class="n">h₀</span> <span class="n">h₁</span> <span class="bp">=></span> <span class="n">contrapose</span><span class="bp">!</span> <span class="n">h₁</span> <span class="n">exact</span> <span class="n">le_antisymm</span> <span class="n">h₀</span> <span class="n">h₁</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬</span><span class="n">y</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="k">match</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="k">with</span> <span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="o">⟨</span><span class="n">h₀</span><span class="o">,</span><span class="w"> </span><span class="n">h₁</span><span class="o">⟩</span><span class="w"> </span><span class="bp">=></span> <span class="w"> </span><span class="n">contrapose</span><span class="bp">!</span><span class="w"> </span><span class="n">h₁</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">le_antisymm</span><span class="w"> </span><span class="n">h₀</span><span class="w"> </span><span class="n">h₁</span> <span class="kd">example</span> <span class="o">{</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">y</span> <span class="bp">∧</span> <span class="n">x</span> <span class="bp">≠</span> <span class="n">y</span><span class="o">)</span> <span class="o">:</span> <span class="bp">¬</span><span class="n">y</span> <span class="bp">≤</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="k">match</span> <span class="n">h</span> <span class="k">with</span> <span class="bp">|</span> <span class="o">⟨</span><span class="n">h₀</span><span class="o">,</span> <span class="n">h₁</span><span class="o">⟩</span> <span class="bp">=></span> <span class="n">contrapose</span><span class="bp">!</span> <span class="n">h₁</span> <span class="n">exact</span> <span class="n">le_antisymm</span> <span class="n">h₀</span> <span class="n">h₁</span> </pre></div> </div> <p>In contrast to using an existential quantifier,
-
@@ -1170,47 +1166,47 @@ you can also extract proofs of the two componentsof a hypothesis <code class="docutils literal notranslate"><span class="pre">h</span> <span class="pre">:</span> <span class="pre">A</span> <span class="pre">∧</span> <span class="pre">B</span></code> by writing <code class="docutils literal notranslate"><span class="pre">h.left</span></code> and <code class="docutils literal notranslate"><span class="pre">h.right</span></code>, or, equivalently, <code class="docutils literal notranslate"><span class="pre">h.1</span></code> and <code class="docutils literal notranslate"><span class="pre">h.2</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬</span><span class="n">y</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">h'</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">h.right</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">le_antisymm</span><span class="w"> </span><span class="n">h.left</span><span class="w"> </span><span class="n">h'</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">y</span> <span class="bp">∧</span> <span class="n">x</span> <span class="bp">≠</span> <span class="n">y</span><span class="o">)</span> <span class="o">:</span> <span class="bp">¬</span><span class="n">y</span> <span class="bp">≤</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">h'</span> <span class="n">apply</span> <span class="n">h.right</span> <span class="n">exact</span> <span class="n">le_antisymm</span> <span class="n">h.left</span> <span class="n">h'</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬</span><span class="n">y</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">h'</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">h.right</span><span class="w"> </span><span class="o">(</span><span class="n">le_antisymm</span><span class="w"> </span><span class="n">h.left</span><span class="w"> </span><span class="n">h'</span><span class="o">)</span> <span class="kd">example</span> <span class="o">{</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">y</span> <span class="bp">∧</span> <span class="n">x</span> <span class="bp">≠</span> <span class="n">y</span><span class="o">)</span> <span class="o">:</span> <span class="bp">¬</span><span class="n">y</span> <span class="bp">≤</span> <span class="n">x</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">h'</span> <span class="bp">↦</span> <span class="n">h.right</span> <span class="o">(</span><span class="n">le_antisymm</span> <span class="n">h.left</span> <span class="n">h'</span><span class="o">)</span> </pre></div> </div> <p>Try using these techniques to come up with various ways of proving of the following:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="bp">¬</span><span class="n">n</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">m</span> <span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">m</span> <span class="bp">∣</span> <span class="n">n</span> <span class="bp">∧</span> <span class="n">m</span> <span class="bp">≠</span> <span class="n">n</span><span class="o">)</span> <span class="o">:</span> <span class="n">m</span> <span class="bp">∣</span> <span class="n">n</span> <span class="bp">∧</span> <span class="bp">¬</span><span class="n">n</span> <span class="bp">∣</span> <span class="n">m</span> <span class="o">:=</span> <span class="gr">sorry</span> </pre></div> </div> <p>You can nest uses of <code class="docutils literal notranslate"><span class="pre">∃</span></code> and <code class="docutils literal notranslate"><span class="pre">∧</span></code> with anonymous constructors, <code class="docutils literal notranslate"><span class="pre">rintro</span></code>, and <code class="docutils literal notranslate"><span class="pre">rcases</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">,</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">⟨</span><span class="mi">5</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="o">,</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">norm_num</span><span class="o">,</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">norm_num</span><span class="o">⟩</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">x</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">,</span> <span class="mi">2</span> <span class="bp"><</span> <span class="n">x</span> <span class="bp">∧</span> <span class="n">x</span> <span class="bp"><</span> <span class="mi">4</span> <span class="o">:=</span> <span class="o">⟨</span><span class="mi">5</span> <span class="bp">/</span> <span class="mi">2</span><span class="o">,</span> <span class="kd">by</span> <span class="n">norm_num</span><span class="o">,</span> <span class="kd">by</span> <span class="n">norm_num</span><span class="o">⟩</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="bp">∃</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">,</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rintro</span><span class="w"> </span><span class="o">⟨</span><span class="n">z</span><span class="o">,</span><span class="w"> </span><span class="n">xltz</span><span class="o">,</span><span class="w"> </span><span class="n">zlty</span><span class="o">⟩</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">lt_trans</span><span class="w"> </span><span class="n">xltz</span><span class="w"> </span><span class="n">zlty</span> <span class="kd">example</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="bp">∃</span> <span class="n">z</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">,</span> <span class="n">x</span> <span class="bp"><</span> <span class="n">z</span> <span class="bp">∧</span> <span class="n">z</span> <span class="bp"><</span> <span class="n">y</span><span class="o">)</span> <span class="bp">→</span> <span class="n">x</span> <span class="bp"><</span> <span class="n">y</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rintro</span> <span class="o">⟨</span><span class="n">z</span><span class="o">,</span> <span class="n">xltz</span><span class="o">,</span> <span class="n">zlty</span><span class="o">⟩</span> <span class="n">exact</span> <span class="n">lt_trans</span> <span class="n">xltz</span> <span class="n">zlty</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="bp">∃</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">,</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="o">⟨</span><span class="n">z</span><span class="o">,</span><span class="w"> </span><span class="n">xltz</span><span class="o">,</span><span class="w"> </span><span class="n">zlty</span><span class="o">⟩</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">lt_trans</span><span class="w"> </span><span class="n">xltz</span><span class="w"> </span><span class="n">zlty</span> <span class="kd">example</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="bp">∃</span> <span class="n">z</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">,</span> <span class="n">x</span> <span class="bp"><</span> <span class="n">z</span> <span class="bp">∧</span> <span class="n">z</span> <span class="bp"><</span> <span class="n">y</span><span class="o">)</span> <span class="bp">→</span> <span class="n">x</span> <span class="bp"><</span> <span class="n">y</span> <span class="o">:=</span> <span class="k">fun</span> <span class="o">⟨</span><span class="n">z</span><span class="o">,</span> <span class="n">xltz</span><span class="o">,</span> <span class="n">zlty</span><span class="o">⟩</span> <span class="bp">↦</span> <span class="n">lt_trans</span> <span class="n">xltz</span> <span class="n">zlty</span> </pre></div> </div> <p>You can also use the <code class="docutils literal notranslate"><span class="pre">use</span></code> tactic:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">,</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span> <span class="w"> </span><span class="n">constructor</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">norm_num</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">x</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">,</span> <span class="mi">2</span> <span class="bp"><</span> <span class="n">x</span> <span class="bp">∧</span> <span class="n">x</span> <span class="bp"><</span> <span class="mi">4</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">use</span> <span class="mi">5</span> <span class="bp">/</span> <span class="mi">2</span> <span class="n">constructor</span> <span class="bp"><;></span> <span class="n">norm_num</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">,</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="mi">10</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">Nat.Prime</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">Nat.Prime</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="mi">5</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="mi">7</span> <span class="w"> </span><span class="n">norm_num</span> <span class="kd">example</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">m</span> <span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">,</span> <span class="mi">4</span> <span class="bp"><</span> <span class="n">m</span> <span class="bp">∧</span> <span class="n">m</span> <span class="bp"><</span> <span class="n">n</span> <span class="bp">∧</span> <span class="n">n</span> <span class="bp"><</span> <span class="mi">10</span> <span class="bp">∧</span> <span class="n">Nat.Prime</span> <span class="n">m</span> <span class="bp">∧</span> <span class="n">Nat.Prime</span> <span class="n">n</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">use</span> <span class="mi">5</span> <span class="n">use</span> <span class="mi">7</span> <span class="n">norm_num</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="bp">¬</span><span class="n">y</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rintro</span><span class="w"> </span><span class="o">⟨</span><span class="n">h₀</span><span class="o">,</span><span class="w"> </span><span class="n">h₁</span><span class="o">⟩</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">h₀</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">h'</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">h₁</span><span class="w"> </span><span class="o">(</span><span class="n">le_antisymm</span><span class="w"> </span><span class="n">h₀</span><span class="w"> </span><span class="n">h'</span><span class="o">)</span> <span class="kd">example</span> <span class="o">{</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">y</span> <span class="bp">∧</span> <span class="n">x</span> <span class="bp">≠</span> <span class="n">y</span> <span class="bp">→</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">y</span> <span class="bp">∧</span> <span class="bp">¬</span><span class="n">y</span> <span class="bp">≤</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rintro</span> <span class="o">⟨</span><span class="n">h₀</span><span class="o">,</span> <span class="n">h₁</span><span class="o">⟩</span> <span class="n">use</span> <span class="n">h₀</span> <span class="n">exact</span> <span class="k">fun</span> <span class="n">h'</span> <span class="bp">↦</span> <span class="n">h₁</span> <span class="o">(</span><span class="n">le_antisymm</span> <span class="n">h₀</span> <span class="n">h'</span><span class="o">)</span> </pre></div> </div> <p>In the first example, the semicolon after the <code class="docutils literal notranslate"><span class="pre">constructor</span></code> command tells Lean to use the
-
@@ -1224,16 +1220,16 @@ You can also use <code class="docutils literal notranslate"><span class="pre">caTo prove an if-and-only-if statement, you can use <code class="docutils literal notranslate"><span class="pre">constructor</span></code> or angle brackets, just as you would if you were proving a conjunction.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬</span><span class="n">y</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">constructor</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">contrapose</span><span class="bp">!</span> <span class="w"> </span><span class="n">rintro</span><span class="w"> </span><span class="n">rfl</span> <span class="w"> </span><span class="n">rfl</span> <span class="w"> </span><span class="n">contrapose</span><span class="bp">!</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">le_antisymm</span><span class="w"> </span><span class="n">h</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">y</span><span class="o">)</span> <span class="o">:</span> <span class="bp">¬</span><span class="n">y</span> <span class="bp">≤</span> <span class="n">x</span> <span class="bp">↔</span> <span class="n">x</span> <span class="bp">≠</span> <span class="n">y</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">constructor</span> <span class="bp">·</span> <span class="n">contrapose</span><span class="bp">!</span> <span class="n">rintro</span> <span class="n">rfl</span> <span class="n">rfl</span> <span class="n">contrapose</span><span class="bp">!</span> <span class="n">exact</span> <span class="n">le_antisymm</span> <span class="n">h</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬</span><span class="n">y</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">⟨</span><span class="k">fun</span><span class="w"> </span><span class="n">h₀</span><span class="w"> </span><span class="n">h₁</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">h₀</span><span class="w"> </span><span class="o">(</span><span class="kd">by</span><span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">h₁</span><span class="o">]),</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">h₀</span><span class="w"> </span><span class="n">h₁</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">h₀</span><span class="w"> </span><span class="o">(</span><span class="n">le_antisymm</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="n">h₁</span><span class="o">)⟩</span> <span class="kd">example</span> <span class="o">{</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">y</span><span class="o">)</span> <span class="o">:</span> <span class="bp">¬</span><span class="n">y</span> <span class="bp">≤</span> <span class="n">x</span> <span class="bp">↔</span> <span class="n">x</span> <span class="bp">≠</span> <span class="n">y</span> <span class="o">:=</span> <span class="o">⟨</span><span class="k">fun</span> <span class="n">h₀</span> <span class="n">h₁</span> <span class="bp">↦</span> <span class="n">h₀</span> <span class="o">(</span><span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">h₁</span><span class="o">]),</span> <span class="k">fun</span> <span class="n">h₀</span> <span class="n">h₁</span> <span class="bp">↦</span> <span class="n">h₀</span> <span class="o">(</span><span class="n">le_antisymm</span> <span class="n">h</span> <span class="n">h₁</span><span class="o">)⟩</span> </pre></div> </div> <p>The last proof term is inscrutable. Remember that you can
-
@@ -1241,8 +1237,8 @@ use underscores while writing an expression like that tosee what Lean expects.</p> <p>Try out the various techniques and gadgets you have just seen in order to prove the following:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="bp">¬</span><span class="n">y</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">y</span> <span class="bp">∧</span> <span class="bp">¬</span><span class="n">y</span> <span class="bp">≤</span> <span class="n">x</span> <span class="bp">↔</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">y</span> <span class="bp">∧</span> <span class="n">x</span> <span class="bp">≠</span> <span class="n">y</span> <span class="o">:=</span> <span class="gr">sorry</span> </pre></div> </div> <p>For a more interesting exercise, show that for any
-
@@ -1250,12 +1246,12 @@ two real numbers <code class="docutils literal notranslate"><span class="pre">x<<code class="docutils literal notranslate"><span class="pre">x^2</span> <span class="pre">+</span> <span class="pre">y^2</span> <span class="pre">=</span> <span class="pre">0</span></code> if and only if <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">=</span> <span class="pre">0</span></code> and <code class="docutils literal notranslate"><span class="pre">y</span> <span class="pre">=</span> <span class="pre">0</span></code>. We suggest proving an auxiliary lemma using <code class="docutils literal notranslate"><span class="pre">linarith</span></code>, <code class="docutils literal notranslate"><span class="pre">pow_two_nonneg</span></code>, and <code class="docutils literal notranslate"><span class="pre">pow_eq_zero</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">aux</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">h'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">pow_eq_zero</span><span class="w"> </span><span class="n">h'</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">aux</span> <span class="o">{</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">+</span> <span class="n">y</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">=</span> <span class="mi">0</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">=</span> <span class="mi">0</span> <span class="o">:=</span> <span class="k">have</span> <span class="n">h'</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">=</span> <span class="mi">0</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="n">pow_eq_zero</span> <span class="n">h'</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">+</span> <span class="n">y</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">=</span> <span class="mi">0</span> <span class="bp">↔</span> <span class="n">x</span> <span class="bp">=</span> <span class="mi">0</span> <span class="bp">∧</span> <span class="n">y</span> <span class="bp">=</span> <span class="mi">0</span> <span class="o">:=</span> <span class="gr">sorry</span> </pre></div> </div> <p>In Lean, bi-implication leads a double-life.
-
@@ -1271,14 +1267,14 @@ replace an expression of the form <code class="docutils literal notranslate"><spby the equivalent expression <code class="docutils literal notranslate"><span class="pre">-</span> <span class="pre">y</span> <span class="pre"><</span> <span class="pre">x</span> <span class="pre">∧</span> <span class="pre">x</span> <span class="pre"><</span> <span class="pre">y</span></code>, and in the one after that we use <code class="docutils literal notranslate"><span class="pre">Nat.dvd_gcd_iff</span></code> to replace an expression of the form <code class="docutils literal notranslate"><span class="pre">m</span> <span class="pre">∣</span> <span class="pre">Nat.gcd</span> <span class="pre">n</span> <span class="pre">k</span></code> by the equivalent expression <code class="docutils literal notranslate"><span class="pre">m</span> <span class="pre">∣</span> <span class="pre">n</span> <span class="pre">∧</span> <span class="pre">m</span> <span class="pre">∣</span> <span class="pre">k</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">|</span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">3</span><span class="bp">|</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="bp">-</span><span class="mi">8</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">abs_lt</span><span class="o">]</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="n">constructor</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">linarith</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="bp">|</span><span class="n">x</span> <span class="bp">+</span> <span class="mi">3</span><span class="bp">|</span> <span class="bp"><</span> <span class="mi">5</span> <span class="bp">→</span> <span class="bp">-</span><span class="mi">8</span> <span class="bp"><</span> <span class="n">x</span> <span class="bp">∧</span> <span class="n">x</span> <span class="bp"><</span> <span class="mi">2</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">abs_lt</span><span class="o">]</span> <span class="n">intro</span> <span class="n">h</span> <span class="n">constructor</span> <span class="bp"><;></span> <span class="n">linarith</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">Nat.gcd</span><span class="w"> </span><span class="mi">6</span><span class="w"> </span><span class="mi">15</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">Nat.dvd_gcd_iff</span><span class="o">]</span> <span class="w"> </span><span class="n">constructor</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">norm_num</span> <span class="kd">example</span> <span class="o">:</span> <span class="mi">3</span> <span class="bp">∣</span> <span class="n">Nat.gcd</span> <span class="mi">6</span> <span class="mi">15</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">Nat.dvd_gcd_iff</span><span class="o">]</span> <span class="n">constructor</span> <span class="bp"><;></span> <span class="n">norm_num</span> </pre></div> </div> <p>See if you can use <code class="docutils literal notranslate"><span class="pre">rw</span></code> with the theorem below
-
@@ -1286,13 +1282,13 @@ to provide a short proof that negation is not anondecreasing function. (Note that <code class="docutils literal notranslate"><span class="pre">push_neg</span></code> won’t unfold definitions for you, so the <code class="docutils literal notranslate"><span class="pre">rw</span> <span class="pre">[Monotone]</span></code> in the proof of the theorem is needed.)</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">not_monotone_iff</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬</span><span class="n">Monotone</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="o">,</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">Monotone</span><span class="o">]</span> <span class="w"> </span><span class="n">push_neg</span> <span class="w"> </span><span class="n">rfl</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">not_monotone_iff</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">:</span> <span class="bp">¬</span><span class="n">Monotone</span> <span class="n">f</span> <span class="bp">↔</span> <span class="bp">∃</span> <span class="n">x</span> <span class="n">y</span><span class="o">,</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">y</span> <span class="bp">∧</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">></span> <span class="n">f</span> <span class="n">y</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">Monotone</span><span class="o">]</span> <span class="n">push_neg</span> <span class="n">rfl</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬</span><span class="n">Monotone</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="bp">-</span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">:</span> <span class="bp">¬</span><span class="n">Monotone</span> <span class="k">fun</span> <span class="n">x</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">↦</span> <span class="bp">-</span><span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>The remaining exercises in this section are designed
-
@@ -1307,12 +1303,12 @@ Lean axiomatizes the associated strict pre-order by<code class="docutils literal notranslate"><span class="pre">a</span> <span class="pre"><</span> <span class="pre">b</span> <span class="pre">↔</span> <span class="pre">a</span> <span class="pre">≤</span> <span class="pre">b</span> <span class="pre">∧</span> <span class="pre">¬</span> <span class="pre">b</span> <span class="pre">≤</span> <span class="pre">a</span></code>. Show that if <code class="docutils literal notranslate"><span class="pre">≤</span></code> is a partial order, then <code class="docutils literal notranslate"><span class="pre">a</span> <span class="pre"><</span> <span class="pre">b</span></code> is equivalent to <code class="docutils literal notranslate"><span class="pre">a</span> <span class="pre">≤</span> <span class="pre">b</span> <span class="pre">∧</span> <span class="pre">a</span> <span class="pre">≠</span> <span class="pre">b</span></code>:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">PartialOrder</span><span class="w"> </span><span class="n">α</span><span class="o">]</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">PartialOrder</span> <span class="n">α</span><span class="o">]</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">α</span><span class="o">)</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">lt_iff_le_not_le</span><span class="o">]</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">a</span> <span class="bp"><</span> <span class="n">b</span> <span class="bp">↔</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">b</span> <span class="bp">∧</span> <span class="n">a</span> <span class="bp">≠</span> <span class="n">b</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">lt_iff_le_not_le</span><span class="o">]</span> <span class="gr">sorry</span> </pre></div> </div> <p id="index-20">Beyond logical operations, you do not need
-
@@ -1328,34 +1324,34 @@ We will come back to the simplifier later,but here we are only relying on the fact that it will use the indicated lemma repeatedly, even if it needs to be instantiated to different values.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Preorder</span><span class="w"> </span><span class="n">α</span><span class="o">]</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Preorder</span> <span class="n">α</span><span class="o">]</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">α</span><span class="o">)</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬</span><span class="n">a</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">lt_iff_le_not_le</span><span class="o">]</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">:</span> <span class="bp">¬</span><span class="n">a</span> <span class="bp"><</span> <span class="n">a</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">lt_iff_le_not_le</span><span class="o">]</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="n">only</span><span class="w"> </span><span class="o">[</span><span class="n">lt_iff_le_not_le</span><span class="o">]</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">a</span> <span class="bp"><</span> <span class="n">b</span> <span class="bp">→</span> <span class="n">b</span> <span class="bp"><</span> <span class="n">c</span> <span class="bp">→</span> <span class="n">a</span> <span class="bp"><</span> <span class="n">c</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> <span class="n">only</span> <span class="o">[</span><span class="n">lt_iff_le_not_le</span><span class="o">]</span> <span class="gr">sorry</span> </pre></div> </div> </section> <section id="disjunction"> <span id="id5"></span><h2><span class="section-number">3.5. </span>Disjunction<a class="headerlink" href="#disjunction" title="Link to this heading"></a></h2> <span id="id5"></span><h2><span class="section-number">3.5. </span>Disjunction<a class="headerlink" href="#disjunction" title="Permalink to this heading"></a></h2> <p id="index-21">The canonical way to prove a disjunction <code class="docutils literal notranslate"><span class="pre">A</span> <span class="pre">∨</span> <span class="pre">B</span></code> is to prove <code class="docutils literal notranslate"><span class="pre">A</span></code> or to prove <code class="docutils literal notranslate"><span class="pre">B</span></code>. The <code class="docutils literal notranslate"><span class="pre">left</span></code> tactic chooses <code class="docutils literal notranslate"><span class="pre">A</span></code>, and the <code class="docutils literal notranslate"><span class="pre">right</span></code> tactic chooses <code class="docutils literal notranslate"><span class="pre">B</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">∨</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="bp">-</span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">left</span> <span class="w"> </span><span class="n">linarith</span><span class="w"> </span><span class="o">[</span><span class="n">pow_two_nonneg</span><span class="w"> </span><span class="n">x</span><span class="o">]</span> <span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">y</span> <span class="bp">></span> <span class="n">x</span> <span class="bp">^</span> <span class="mi">2</span><span class="o">)</span> <span class="o">:</span> <span class="n">y</span> <span class="bp">></span> <span class="mi">0</span> <span class="bp">∨</span> <span class="n">y</span> <span class="bp"><</span> <span class="bp">-</span><span class="mi">1</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">left</span> <span class="n">linarith</span> <span class="o">[</span><span class="n">pow_two_nonneg</span> <span class="n">x</span><span class="o">]</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">-</span><span class="n">y</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">∨</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="bp">-</span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">right</span> <span class="w"> </span><span class="n">linarith</span><span class="w"> </span><span class="o">[</span><span class="n">pow_two_nonneg</span><span class="w"> </span><span class="n">x</span><span class="o">]</span> <span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="bp">-</span><span class="n">y</span> <span class="bp">></span> <span class="n">x</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">+</span> <span class="mi">1</span><span class="o">)</span> <span class="o">:</span> <span class="n">y</span> <span class="bp">></span> <span class="mi">0</span> <span class="bp">∨</span> <span class="n">y</span> <span class="bp"><</span> <span class="bp">-</span><span class="mi">1</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">right</span> <span class="n">linarith</span> <span class="o">[</span><span class="n">pow_two_nonneg</span> <span class="n">x</span><span class="o">]</span> </pre></div> </div> <p>We cannot use an anonymous constructor to construct a proof
-
@@ -1366,11 +1362,11 @@ When we write proof terms we can useto make the choice explicitly. Here, <code class="docutils literal notranslate"><span class="pre">inl</span></code> is short for “introduction left” and <code class="docutils literal notranslate"><span class="pre">inr</span></code> is short for “introduction right.”</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">∨</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="bp">-</span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Or.inl</span><span class="w"> </span><span class="n">h</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">y</span> <span class="bp">></span> <span class="mi">0</span><span class="o">)</span> <span class="o">:</span> <span class="n">y</span> <span class="bp">></span> <span class="mi">0</span> <span class="bp">∨</span> <span class="n">y</span> <span class="bp"><</span> <span class="bp">-</span><span class="mi">1</span> <span class="o">:=</span> <span class="n">Or.inl</span> <span class="n">h</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="bp">-</span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">∨</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="bp">-</span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Or.inr</span><span class="w"> </span><span class="n">h</span> <span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">y</span> <span class="bp"><</span> <span class="bp">-</span><span class="mi">1</span><span class="o">)</span> <span class="o">:</span> <span class="n">y</span> <span class="bp">></span> <span class="mi">0</span> <span class="bp">∨</span> <span class="n">y</span> <span class="bp"><</span> <span class="bp">-</span><span class="mi">1</span> <span class="o">:=</span> <span class="n">Or.inr</span> <span class="n">h</span> </pre></div> </div> <p>It may seem strange to prove a disjunction by proving one side
-
@@ -1391,12 +1387,12 @@ the <code class="docutils literal notranslate"><span class="pre">rcases</span></As usual, we can tell Lean what names to use for the hypotheses. In the next example, we tell Lean to use the name <code class="docutils literal notranslate"><span class="pre">h</span></code> on each branch.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="bp">|</span><span class="n">y</span><span class="bp">|</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∨</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="bp">-</span><span class="n">y</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">le_or_gt</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">abs_of_nonneg</span><span class="w"> </span><span class="n">h</span><span class="o">]</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">h</span><span class="bp">;</span><span class="w"> </span><span class="n">left</span><span class="bp">;</span><span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">abs_of_neg</span><span class="w"> </span><span class="n">h</span><span class="o">]</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">h</span><span class="bp">;</span><span class="w"> </span><span class="n">right</span><span class="bp">;</span><span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">h</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">x</span> <span class="bp"><</span> <span class="bp">|</span><span class="n">y</span><span class="bp">|</span> <span class="bp">→</span> <span class="n">x</span> <span class="bp"><</span> <span class="n">y</span> <span class="bp">∨</span> <span class="n">x</span> <span class="bp"><</span> <span class="bp">-</span><span class="n">y</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rcases</span> <span class="n">le_or_gt</span> <span class="mi">0</span> <span class="n">y</span> <span class="k">with</span> <span class="n">h</span> <span class="bp">|</span> <span class="n">h</span> <span class="bp">·</span> <span class="n">rw</span> <span class="o">[</span><span class="n">abs_of_nonneg</span> <span class="n">h</span><span class="o">]</span> <span class="n">intro</span> <span class="n">h</span><span class="bp">;</span> <span class="n">left</span><span class="bp">;</span> <span class="n">exact</span> <span class="n">h</span> <span class="bp">·</span> <span class="n">rw</span> <span class="o">[</span><span class="n">abs_of_neg</span> <span class="n">h</span><span class="o">]</span> <span class="n">intro</span> <span class="n">h</span><span class="bp">;</span> <span class="n">right</span><span class="bp">;</span> <span class="n">exact</span> <span class="n">h</span> </pre></div> </div> <p>Notice that the pattern changes from <code class="docutils literal notranslate"><span class="pre">⟨h₀,</span> <span class="pre">h₁⟩</span></code> in the case of
-
@@ -1417,14 +1413,14 @@ allowing us to split on those two cases.</p>syntax for disjunction. Now the <code class="docutils literal notranslate"><span class="pre">cases</span></code> tactic is more attractive, because it allows us to name each <code class="docutils literal notranslate"><span class="pre">case</span></code>, and name the hypothesis that is introduced closer to where it is used.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="bp">|</span><span class="n">y</span><span class="bp">|</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∨</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="bp">-</span><span class="n">y</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">cases</span><span class="w"> </span><span class="n">le_or_gt</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="n">y</span> <span class="w"> </span><span class="n">case</span><span class="w"> </span><span class="n">inl</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="bp">=></span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">abs_of_nonneg</span><span class="w"> </span><span class="n">h</span><span class="o">]</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">h</span><span class="bp">;</span><span class="w"> </span><span class="n">left</span><span class="bp">;</span><span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="n">case</span><span class="w"> </span><span class="n">inr</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="bp">=></span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">abs_of_neg</span><span class="w"> </span><span class="n">h</span><span class="o">]</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">h</span><span class="bp">;</span><span class="w"> </span><span class="n">right</span><span class="bp">;</span><span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">h</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">x</span> <span class="bp"><</span> <span class="bp">|</span><span class="n">y</span><span class="bp">|</span> <span class="bp">→</span> <span class="n">x</span> <span class="bp"><</span> <span class="n">y</span> <span class="bp">∨</span> <span class="n">x</span> <span class="bp"><</span> <span class="bp">-</span><span class="n">y</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">cases</span> <span class="n">le_or_gt</span> <span class="mi">0</span> <span class="n">y</span> <span class="n">case</span> <span class="n">inl</span> <span class="n">h</span> <span class="bp">=></span> <span class="n">rw</span> <span class="o">[</span><span class="n">abs_of_nonneg</span> <span class="n">h</span><span class="o">]</span> <span class="n">intro</span> <span class="n">h</span><span class="bp">;</span> <span class="n">left</span><span class="bp">;</span> <span class="n">exact</span> <span class="n">h</span> <span class="n">case</span> <span class="n">inr</span> <span class="n">h</span> <span class="bp">=></span> <span class="n">rw</span> <span class="o">[</span><span class="n">abs_of_neg</span> <span class="n">h</span><span class="o">]</span> <span class="n">intro</span> <span class="n">h</span><span class="bp">;</span> <span class="n">right</span><span class="bp">;</span> <span class="n">exact</span> <span class="n">h</span> </pre></div> </div> <p>The names <code class="docutils literal notranslate"><span class="pre">inl</span></code> and <code class="docutils literal notranslate"><span class="pre">inr</span></code> are short for “intro left” and “intro right,”
-
@@ -1432,23 +1428,23 @@ respectively. Using <code class="docutils literal notranslate"><span class="pre"cases in either order; Lean uses the tag to find the relevant goal. If you don’t care about that, you can use <code class="docutils literal notranslate"><span class="pre">next</span></code>, or <code class="docutils literal notranslate"><span class="pre">match</span></code>, or even a pattern-matching <code class="docutils literal notranslate"><span class="pre">have</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="bp">|</span><span class="n">y</span><span class="bp">|</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∨</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="bp">-</span><span class="n">y</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">cases</span><span class="w"> </span><span class="n">le_or_gt</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="n">y</span> <span class="w"> </span><span class="n">next</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="bp">=></span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">abs_of_nonneg</span><span class="w"> </span><span class="n">h</span><span class="o">]</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">h</span><span class="bp">;</span><span class="w"> </span><span class="n">left</span><span class="bp">;</span><span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="n">next</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="bp">=></span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">abs_of_neg</span><span class="w"> </span><span class="n">h</span><span class="o">]</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">h</span><span class="bp">;</span><span class="w"> </span><span class="n">right</span><span class="bp">;</span><span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">h</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="bp">|</span><span class="n">y</span><span class="bp">|</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∨</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="bp">-</span><span class="n">y</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="k">match</span><span class="w"> </span><span class="n">le_or_gt</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="k">with</span> <span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">Or.inl</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="bp">=></span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">abs_of_nonneg</span><span class="w"> </span><span class="n">h</span><span class="o">]</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">h</span><span class="bp">;</span><span class="w"> </span><span class="n">left</span><span class="bp">;</span><span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">Or.inr</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="bp">=></span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">abs_of_neg</span><span class="w"> </span><span class="n">h</span><span class="o">]</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">h</span><span class="bp">;</span><span class="w"> </span><span class="n">right</span><span class="bp">;</span><span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">h</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">x</span> <span class="bp"><</span> <span class="bp">|</span><span class="n">y</span><span class="bp">|</span> <span class="bp">→</span> <span class="n">x</span> <span class="bp"><</span> <span class="n">y</span> <span class="bp">∨</span> <span class="n">x</span> <span class="bp"><</span> <span class="bp">-</span><span class="n">y</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">cases</span> <span class="n">le_or_gt</span> <span class="mi">0</span> <span class="n">y</span> <span class="n">next</span> <span class="n">h</span> <span class="bp">=></span> <span class="n">rw</span> <span class="o">[</span><span class="n">abs_of_nonneg</span> <span class="n">h</span><span class="o">]</span> <span class="n">intro</span> <span class="n">h</span><span class="bp">;</span> <span class="n">left</span><span class="bp">;</span> <span class="n">exact</span> <span class="n">h</span> <span class="n">next</span> <span class="n">h</span> <span class="bp">=></span> <span class="n">rw</span> <span class="o">[</span><span class="n">abs_of_neg</span> <span class="n">h</span><span class="o">]</span> <span class="n">intro</span> <span class="n">h</span><span class="bp">;</span> <span class="n">right</span><span class="bp">;</span> <span class="n">exact</span> <span class="n">h</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">x</span> <span class="bp"><</span> <span class="bp">|</span><span class="n">y</span><span class="bp">|</span> <span class="bp">→</span> <span class="n">x</span> <span class="bp"><</span> <span class="n">y</span> <span class="bp">∨</span> <span class="n">x</span> <span class="bp"><</span> <span class="bp">-</span><span class="n">y</span> <span class="o">:=</span> <span class="kd">by</span> <span class="k">match</span> <span class="n">le_or_gt</span> <span class="mi">0</span> <span class="n">y</span> <span class="k">with</span> <span class="bp">|</span> <span class="n">Or.inl</span> <span class="n">h</span> <span class="bp">=></span> <span class="n">rw</span> <span class="o">[</span><span class="n">abs_of_nonneg</span> <span class="n">h</span><span class="o">]</span> <span class="n">intro</span> <span class="n">h</span><span class="bp">;</span> <span class="n">left</span><span class="bp">;</span> <span class="n">exact</span> <span class="n">h</span> <span class="bp">|</span> <span class="n">Or.inr</span> <span class="n">h</span> <span class="bp">=></span> <span class="n">rw</span> <span class="o">[</span><span class="n">abs_of_neg</span> <span class="n">h</span><span class="o">]</span> <span class="n">intro</span> <span class="n">h</span><span class="bp">;</span> <span class="n">right</span><span class="bp">;</span> <span class="n">exact</span> <span class="n">h</span> </pre></div> </div> <p>In the case of <code class="docutils literal notranslate"><span class="pre">match</span></code>, we need to use the full names
-
@@ -1458,54 +1454,54 @@ cases of a disjunction.</p><p>Try proving the triangle inequality using the first two theorems in the next snippet. They are given the same names they have in Mathlib.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">namespace</span><span class="w"> </span><span class="n">MyAbs</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">namespace</span> <span class="n">MyAbs</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">le_abs_self</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="bp">|</span><span class="n">x</span><span class="bp">|</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">theorem</span> <span class="n">le_abs_self</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≤</span> <span class="bp">|</span><span class="n">x</span><span class="bp">|</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">neg_le_abs_self</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">-</span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="bp">|</span><span class="n">x</span><span class="bp">|</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">theorem</span> <span class="n">neg_le_abs_self</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="bp">-</span><span class="n">x</span> <span class="bp">≤</span> <span class="bp">|</span><span class="n">x</span><span class="bp">|</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">abs_add</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">|</span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y</span><span class="bp">|</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="bp">|</span><span class="n">x</span><span class="bp">|</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="bp">|</span><span class="n">y</span><span class="bp">|</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">theorem</span> <span class="n">abs_add</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="bp">|</span><span class="n">x</span> <span class="bp">+</span> <span class="n">y</span><span class="bp">|</span> <span class="bp">≤</span> <span class="bp">|</span><span class="n">x</span><span class="bp">|</span> <span class="bp">+</span> <span class="bp">|</span><span class="n">y</span><span class="bp">|</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>In case you enjoyed these (pun intended) and you want more practice with disjunction, try these.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">lt_abs</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="bp">|</span><span class="n">y</span><span class="bp">|</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∨</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="bp">-</span><span class="n">y</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">lt_abs</span> <span class="o">:</span> <span class="n">x</span> <span class="bp"><</span> <span class="bp">|</span><span class="n">y</span><span class="bp">|</span> <span class="bp">↔</span> <span class="n">x</span> <span class="bp"><</span> <span class="n">y</span> <span class="bp">∨</span> <span class="n">x</span> <span class="bp"><</span> <span class="bp">-</span><span class="n">y</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">abs_lt</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">|</span><span class="n">x</span><span class="bp">|</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="bp">-</span><span class="n">y</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">theorem</span> <span class="n">abs_lt</span> <span class="o">:</span> <span class="bp">|</span><span class="n">x</span><span class="bp">|</span> <span class="bp"><</span> <span class="n">y</span> <span class="bp">↔</span> <span class="bp">-</span><span class="n">y</span> <span class="bp"><</span> <span class="n">x</span> <span class="bp">∧</span> <span class="n">x</span> <span class="bp"><</span> <span class="n">y</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>You can also use <code class="docutils literal notranslate"><span class="pre">rcases</span></code> and <code class="docutils literal notranslate"><span class="pre">rintro</span></code> with nested disjunctions. When these result in a genuine case split with multiple goals, the patterns for each new goal are separated by a vertical bar.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">∨</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">lt_trichotomy</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="n">xlt</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">xeq</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">xgt</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">left</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">xlt</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">contradiction</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">right</span><span class="bp">;</span><span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">xgt</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">x</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">≠</span> <span class="mi">0</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp"><</span> <span class="mi">0</span> <span class="bp">∨</span> <span class="n">x</span> <span class="bp">></span> <span class="mi">0</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rcases</span> <span class="n">lt_trichotomy</span> <span class="n">x</span> <span class="mi">0</span> <span class="k">with</span> <span class="n">xlt</span> <span class="bp">|</span> <span class="n">xeq</span> <span class="bp">|</span> <span class="n">xgt</span> <span class="bp">·</span> <span class="n">left</span> <span class="n">exact</span> <span class="n">xlt</span> <span class="bp">·</span> <span class="n">contradiction</span> <span class="bp">·</span> <span class="n">right</span><span class="bp">;</span> <span class="n">exact</span> <span class="n">xgt</span> </pre></div> </div> <p>You can still nest patterns and use the <code class="docutils literal notranslate"><span class="pre">rfl</span></code> keyword to substitute equations:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">k</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">∨</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">k</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">k</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="n">rfl</span><span class="o">⟩</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="o">⟨</span><span class="n">b</span><span class="o">,</span><span class="w"> </span><span class="n">rfl</span><span class="o">⟩</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">mul_assoc</span><span class="o">]</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">dvd_mul_right</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">mul_comm</span><span class="o">,</span><span class="w"> </span><span class="n">mul_assoc</span><span class="o">]</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">dvd_mul_right</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">m</span> <span class="n">n</span> <span class="n">k</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">m</span> <span class="bp">∣</span> <span class="n">n</span> <span class="bp">∨</span> <span class="n">m</span> <span class="bp">∣</span> <span class="n">k</span><span class="o">)</span> <span class="o">:</span> <span class="n">m</span> <span class="bp">∣</span> <span class="n">n</span> <span class="bp">*</span> <span class="n">k</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rcases</span> <span class="n">h</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">a</span><span class="o">,</span> <span class="n">rfl</span><span class="o">⟩</span> <span class="bp">|</span> <span class="o">⟨</span><span class="n">b</span><span class="o">,</span> <span class="n">rfl</span><span class="o">⟩</span> <span class="bp">·</span> <span class="n">rw</span> <span class="o">[</span><span class="n">mul_assoc</span><span class="o">]</span> <span class="n">apply</span> <span class="n">dvd_mul_right</span> <span class="bp">·</span> <span class="n">rw</span> <span class="o">[</span><span class="n">mul_comm</span><span class="o">,</span> <span class="n">mul_assoc</span><span class="o">]</span> <span class="n">apply</span> <span class="n">dvd_mul_right</span> </pre></div> </div> <p>See if you can prove the following with a single (long) line. Use <code class="docutils literal notranslate"><span class="pre">rcases</span></code> to unpack the hypotheses and split on cases, and use a semicolon and <code class="docutils literal notranslate"><span class="pre">linarith</span></code> to solve each branch.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">z</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="o">,</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">∨</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp">≥</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">z</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">x</span> <span class="n">y</span><span class="o">,</span> <span class="n">z</span> <span class="bp">=</span> <span class="n">x</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">+</span> <span class="n">y</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">∨</span> <span class="n">z</span> <span class="bp">=</span> <span class="n">x</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">+</span> <span class="n">y</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">+</span> <span class="mi">1</span><span class="o">)</span> <span class="o">:</span> <span class="n">z</span> <span class="bp">≥</span> <span class="mi">0</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>On the real numbers, an equation <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">*</span> <span class="pre">y</span> <span class="pre">=</span> <span class="pre">0</span></code>
-
@@ -1513,11 +1509,11 @@ tells us that <code class="docutils literal notranslate"><span class="pre">x</spIn Mathlib, this fact is known as <code class="docutils literal notranslate"><span class="pre">eq_zero_or_eq_zero_of_mul_eq_zero</span></code>, and it is another nice example of how a disjunction can arise. See if you can use it to prove the following:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">∨</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">-</span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">x</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">=</span> <span class="mi">1</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">=</span> <span class="mi">1</span> <span class="bp">∨</span> <span class="n">x</span> <span class="bp">=</span> <span class="bp">-</span><span class="mi">1</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∨</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">-</span><span class="n">y</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">{</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">=</span> <span class="n">y</span> <span class="bp">^</span> <span class="mi">2</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">=</span> <span class="n">y</span> <span class="bp">∨</span> <span class="n">x</span> <span class="bp">=</span> <span class="bp">-</span><span class="n">y</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>Remember that you can use the <code class="docutils literal notranslate"><span class="pre">ring</span></code> tactic to help
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@@ -1535,14 +1531,14 @@ says that the real numbers have no nontrivial zero divisors.A commutative ring with this property is called an <em>integral domain</em>. Your proofs of the two theorems above should work equally well in any integral domain:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">R</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">CommRing</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">IsDomain</span><span class="w"> </span><span class="n">R</span><span class="o">]</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">R</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">CommRing</span> <span class="n">R</span><span class="o">]</span> <span class="o">[</span><span class="n">IsDomain</span> <span class="n">R</span><span class="o">]</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">∨</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">-</span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">=</span> <span class="mi">1</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">=</span> <span class="mi">1</span> <span class="bp">∨</span> <span class="n">x</span> <span class="bp">=</span> <span class="bp">-</span><span class="mi">1</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∨</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">-</span><span class="n">y</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">=</span> <span class="n">y</span> <span class="bp">^</span> <span class="mi">2</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">=</span> <span class="n">y</span> <span class="bp">∨</span> <span class="n">x</span> <span class="bp">=</span> <span class="bp">-</span><span class="n">y</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>In fact, if you are careful, you can prove the first
-
@@ -1554,19 +1550,19 @@ depending on whether some statement is true or not.For any proposition <code class="docutils literal notranslate"><span class="pre">P</span></code>, we can use <code class="docutils literal notranslate"><span class="pre">em</span> <span class="pre">P</span> <span class="pre">:</span> <span class="pre">P</span> <span class="pre">∨</span> <span class="pre">¬</span> <span class="pre">P</span></code>. The name <code class="docutils literal notranslate"><span class="pre">em</span></code> is short for “excluded middle.”</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">P</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Prop</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬¬</span><span class="n">P</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="n">cases</span><span class="w"> </span><span class="n">em</span><span class="w"> </span><span class="n">P</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">assumption</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">contradiction</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">P</span> <span class="o">:</span> <span class="kt">Prop</span><span class="o">)</span> <span class="o">:</span> <span class="bp">¬¬</span><span class="n">P</span> <span class="bp">→</span> <span class="n">P</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">h</span> <span class="n">cases</span> <span class="n">em</span> <span class="n">P</span> <span class="bp">·</span> <span class="n">assumption</span> <span class="bp">·</span> <span class="n">contradiction</span> </pre></div> </div> <p id="index-23">Alternatively, you can use the <code class="docutils literal notranslate"><span class="pre">by_cases</span></code> tactic.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">P</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Prop</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬¬</span><span class="n">P</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="n">by_cases</span><span class="w"> </span><span class="n">h'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">P</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">assumption</span> <span class="w"> </span><span class="n">contradiction</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">P</span> <span class="o">:</span> <span class="kt">Prop</span><span class="o">)</span> <span class="o">:</span> <span class="bp">¬¬</span><span class="n">P</span> <span class="bp">→</span> <span class="n">P</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">h</span> <span class="n">by_cases</span> <span class="n">h'</span> <span class="o">:</span> <span class="n">P</span> <span class="bp">·</span> <span class="n">assumption</span> <span class="n">contradiction</span> </pre></div> </div> <p>Notice that the <code class="docutils literal notranslate"><span class="pre">by_cases</span></code> tactic lets you
-
@@ -1578,13 +1574,13 @@ If you leave out the label,Lean uses <code class="docutils literal notranslate"><span class="pre">h</span></code> by default. Try proving the following equivalence, using <code class="docutils literal notranslate"><span class="pre">by_cases</span></code> to establish one direction.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">P</span><span class="w"> </span><span class="n">Q</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Prop</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Q</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="bp">¬</span><span class="n">P</span><span class="w"> </span><span class="bp">∨</span><span class="w"> </span><span class="n">Q</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">P</span> <span class="n">Q</span> <span class="o">:</span> <span class="kt">Prop</span><span class="o">)</span> <span class="o">:</span> <span class="n">P</span> <span class="bp">→</span> <span class="n">Q</span> <span class="bp">↔</span> <span class="bp">¬</span><span class="n">P</span> <span class="bp">∨</span> <span class="n">Q</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> </section> <section id="sequences-and-convergence"> <span id="id6"></span><h2><span class="section-number">3.6. </span>Sequences and Convergence<a class="headerlink" href="#sequences-and-convergence" title="Link to this heading"></a></h2> <span id="id6"></span><h2><span class="section-number">3.6. </span>Sequences and Convergence<a class="headerlink" href="#sequences-and-convergence" title="Permalink to this heading"></a></h2> <p>We now have enough skills at our disposal to do some real mathematics. In Lean, we can represent a sequence <span class="math notranslate nohighlight">\(s_0, s_1, s_2, \ldots\)</span> of real numbers as a function <code class="docutils literal notranslate"><span class="pre">s</span> <span class="pre">:</span> <span class="pre">ℕ</span> <span class="pre">→</span> <span class="pre">ℝ</span></code>.
-
@@ -1594,8 +1590,8 @@ remains within <span class="math notranslate nohighlight">\(\varepsilon\)</span>that is, there is a number <span class="math notranslate nohighlight">\(N\)</span> such that for every <span class="math notranslate nohighlight">\(n \ge N\)</span>, <span class="math notranslate nohighlight">\(| s_n - a | < \varepsilon\)</span>. In Lean, we can render this as follows:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">ConvergesTo</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span><span class="o">,</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">N</span><span class="o">,</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">≥</span><span class="w"> </span><span class="n">N</span><span class="o">,</span><span class="w"> </span><span class="bp">|</span><span class="n">s</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">a</span><span class="bp">|</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">ConvergesTo</span> <span class="o">(</span><span class="n">s</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:=</span> <span class="bp">∀</span> <span class="n">ε</span> <span class="bp">></span> <span class="mi">0</span><span class="o">,</span> <span class="bp">∃</span> <span class="n">N</span><span class="o">,</span> <span class="bp">∀</span> <span class="n">n</span> <span class="bp">≥</span> <span class="n">N</span><span class="o">,</span> <span class="bp">|</span><span class="n">s</span> <span class="n">n</span> <span class="bp">-</span> <span class="n">a</span><span class="bp">|</span> <span class="bp"><</span> <span class="n">ε</span> </pre></div> </div> <p>The notation <code class="docutils literal notranslate"><span class="pre">∀</span> <span class="pre">ε</span> <span class="pre">></span> <span class="pre">0,</span> <span class="pre">...</span></code> is a convenient abbreviation
-
@@ -1615,9 +1611,9 @@ value for every <span class="math notranslate nohighlight">\(x\)</span>.The <code class="docutils literal notranslate"><span class="pre">ext</span></code> tactic enables us to prove an equation between functions by proving that their values are the same at all the values of their arguments.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">ext</span> <span class="w"> </span><span class="n">ring</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="o">(</span><span class="k">fun</span> <span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">↦</span> <span class="o">(</span><span class="n">x</span> <span class="bp">+</span> <span class="n">y</span><span class="o">)</span> <span class="bp">^</span> <span class="mi">2</span><span class="o">)</span> <span class="bp">=</span> <span class="k">fun</span> <span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">↦</span> <span class="n">x</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">+</span> <span class="mi">2</span> <span class="bp">*</span> <span class="n">x</span> <span class="bp">*</span> <span class="n">y</span> <span class="bp">+</span> <span class="n">y</span> <span class="bp">^</span> <span class="mi">2</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">ext</span> <span class="n">ring</span> </pre></div> </div> <p id="index-25">We’ll see later that <code class="docutils literal notranslate"><span class="pre">ext</span></code> is actually more general, and also one can
-
@@ -1627,9 +1623,9 @@ above proof.The second tactic, the <code class="docutils literal notranslate"><span class="pre">congr</span></code> tactic, allows us to prove an equation between two expressions by reconciling the parts that are different:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">|</span><span class="n">a</span><span class="bp">|</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">|</span><span class="n">a</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="bp">|</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">congr</span> <span class="w"> </span><span class="n">ring</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="bp">|</span><span class="n">a</span><span class="bp">|</span> <span class="bp">=</span> <span class="bp">|</span><span class="n">a</span> <span class="bp">-</span> <span class="n">b</span> <span class="bp">+</span> <span class="n">b</span><span class="bp">|</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">congr</span> <span class="n">ring</span> </pre></div> </div> <p>Here the <code class="docutils literal notranslate"><span class="pre">congr</span></code> tactic peels off the <code class="docutils literal notranslate"><span class="pre">abs</span></code> on each side,
-
@@ -1645,10 +1641,10 @@ Instead, the <code class="docutils literal notranslate"><span class="pre">converas it is, and leaves us with the task of proving the equations that are needed to make the goal match.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">convert</span><span class="w"> </span><span class="o">(</span><span class="n">mul_lt_mul_right</span><span class="w"> </span><span class="n">_</span><span class="o">)</span><span class="bp">.</span><span class="mi">2</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">one_mul</span><span class="o">]</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">lt_trans</span><span class="w"> </span><span class="n">zero_lt_one</span><span class="w"> </span><span class="n">h</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">a</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="mi">1</span> <span class="bp"><</span> <span class="n">a</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp"><</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">a</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">convert</span> <span class="o">(</span><span class="n">mul_lt_mul_right</span> <span class="n">_</span><span class="o">)</span><span class="bp">.</span><span class="mi">2</span> <span class="n">h</span> <span class="bp">·</span> <span class="n">rw</span> <span class="o">[</span><span class="n">one_mul</span><span class="o">]</span> <span class="n">exact</span> <span class="n">lt_trans</span> <span class="n">zero_lt_one</span> <span class="n">h</span> </pre></div> </div> <p>This example illustrates another useful trick: when we apply an
-
@@ -1657,12 +1653,12 @@ and Lean can’t fill it in for us automatically,it simply leaves it for us as another goal.</p> <p>The following shows that any constant sequence <span class="math notranslate nohighlight">\(a, a, a, \ldots\)</span> converges.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">convergesTo_const</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ConvergesTo</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="n">εpos</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="mi">0</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">nge</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">sub_self</span><span class="o">,</span><span class="w"> </span><span class="n">abs_zero</span><span class="o">]</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">εpos</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">convergesTo_const</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="n">ConvergesTo</span> <span class="o">(</span><span class="k">fun</span> <span class="n">x</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">↦</span> <span class="n">a</span><span class="o">)</span> <span class="n">a</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">ε</span> <span class="n">εpos</span> <span class="n">use</span> <span class="mi">0</span> <span class="n">intro</span> <span class="n">n</span> <span class="n">nge</span> <span class="n">rw</span> <span class="o">[</span><span class="n">sub_self</span><span class="o">,</span> <span class="n">abs_zero</span><span class="o">]</span> <span class="n">apply</span> <span class="n">εpos</span> </pre></div> </div> <p>Lean has a tactic, <code class="docutils literal notranslate"><span class="pre">simp</span></code>, which can often save you the
-
@@ -1686,16 +1682,16 @@ the sequence <code class="docutils literal notranslate"><span class="pre">fun</sof <code class="docutils literal notranslate"><span class="pre">a</span> <span class="pre">+</span> <span class="pre">b</span></code>. The following example begins to implement this strategy. See if you can finish it off.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">convergesTo_add</span><span class="w"> </span><span class="o">{</span><span class="n">s</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span> <span class="w"> </span><span class="o">(</span><span class="n">cs</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ConvergesTo</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">ct</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ConvergesTo</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">ConvergesTo</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="n">εpos</span> <span class="w"> </span><span class="n">dsimp</span><span class="w"> </span><span class="c1">-- this line is not needed but cleans up the goal a bit.</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">ε2pos</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">linarith</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">cs</span><span class="w"> </span><span class="o">(</span><span class="n">ε</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="n">ε2pos</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">Ns</span><span class="o">,</span><span class="w"> </span><span class="n">hs</span><span class="o">⟩</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">ct</span><span class="w"> </span><span class="o">(</span><span class="n">ε</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="n">ε2pos</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">Nt</span><span class="o">,</span><span class="w"> </span><span class="n">ht</span><span class="o">⟩</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">max</span><span class="w"> </span><span class="n">Ns</span><span class="w"> </span><span class="n">Nt</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">convergesTo_add</span> <span class="o">{</span><span class="n">s</span> <span class="n">t</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">{</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">cs</span> <span class="o">:</span> <span class="n">ConvergesTo</span> <span class="n">s</span> <span class="n">a</span><span class="o">)</span> <span class="o">(</span><span class="n">ct</span> <span class="o">:</span> <span class="n">ConvergesTo</span> <span class="n">t</span> <span class="n">b</span><span class="o">)</span> <span class="o">:</span> <span class="n">ConvergesTo</span> <span class="o">(</span><span class="k">fun</span> <span class="n">n</span> <span class="bp">↦</span> <span class="n">s</span> <span class="n">n</span> <span class="bp">+</span> <span class="n">t</span> <span class="n">n</span><span class="o">)</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">ε</span> <span class="n">εpos</span> <span class="n">dsimp</span> <span class="c1">-- this line is not needed but cleans up the goal a bit.</span> <span class="k">have</span> <span class="n">ε2pos</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp"><</span> <span class="n">ε</span> <span class="bp">/</span> <span class="mi">2</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">linarith</span> <span class="n">rcases</span> <span class="n">cs</span> <span class="o">(</span><span class="n">ε</span> <span class="bp">/</span> <span class="mi">2</span><span class="o">)</span> <span class="n">ε2pos</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">Ns</span><span class="o">,</span> <span class="n">hs</span><span class="o">⟩</span> <span class="n">rcases</span> <span class="n">ct</span> <span class="o">(</span><span class="n">ε</span> <span class="bp">/</span> <span class="mi">2</span><span class="o">)</span> <span class="n">ε2pos</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">Nt</span><span class="o">,</span> <span class="n">ht</span><span class="o">⟩</span> <span class="n">use</span> <span class="n">max</span> <span class="n">Ns</span> <span class="n">Nt</span> <span class="gr">sorry</span> </pre></div> </div> <p>As hints, you can use <code class="docutils literal notranslate"><span class="pre">le_of_max_le_left</span></code> and <code class="docutils literal notranslate"><span class="pre">le_of_max_le_right</span></code>,
-
@@ -1717,27 +1713,27 @@ is equal to zero or not.We have taken care of the zero case, and we have left you to prove the result with the extra assumption that <code class="docutils literal notranslate"><span class="pre">c</span></code> is nonzero.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">convergesTo_mul_const</span><span class="w"> </span><span class="o">{</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">cs</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ConvergesTo</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">ConvergesTo</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">c</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">by_cases</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">convert</span><span class="w"> </span><span class="n">convergesTo_const</span><span class="w"> </span><span class="mi">0</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">h</span><span class="o">]</span> <span class="w"> </span><span class="n">ring</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">h</span><span class="o">]</span> <span class="w"> </span><span class="n">ring</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">acpos</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="bp">|</span><span class="n">c</span><span class="bp">|</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">abs_pos.mpr</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">convergesTo_mul_const</span> <span class="o">{</span><span class="n">s</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">{</span><span class="n">a</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">c</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">cs</span> <span class="o">:</span> <span class="n">ConvergesTo</span> <span class="n">s</span> <span class="n">a</span><span class="o">)</span> <span class="o">:</span> <span class="n">ConvergesTo</span> <span class="o">(</span><span class="k">fun</span> <span class="n">n</span> <span class="bp">↦</span> <span class="n">c</span> <span class="bp">*</span> <span class="n">s</span> <span class="n">n</span><span class="o">)</span> <span class="o">(</span><span class="n">c</span> <span class="bp">*</span> <span class="n">a</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">by_cases</span> <span class="n">h</span> <span class="o">:</span> <span class="n">c</span> <span class="bp">=</span> <span class="mi">0</span> <span class="bp">·</span> <span class="n">convert</span> <span class="n">convergesTo_const</span> <span class="mi">0</span> <span class="bp">·</span> <span class="n">rw</span> <span class="o">[</span><span class="n">h</span><span class="o">]</span> <span class="n">ring</span> <span class="n">rw</span> <span class="o">[</span><span class="n">h</span><span class="o">]</span> <span class="n">ring</span> <span class="k">have</span> <span class="n">acpos</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp"><</span> <span class="bp">|</span><span class="n">c</span><span class="bp">|</span> <span class="o">:=</span> <span class="n">abs_pos.mpr</span> <span class="n">h</span> <span class="gr">sorry</span> </pre></div> </div> <p>The next theorem is also independently interesting: it shows that a convergent sequence is eventually bounded in absolute value. We have started you off; see if you can finish it.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">exists_abs_le_of_convergesTo</span><span class="w"> </span><span class="o">{</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">cs</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ConvergesTo</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="n">b</span><span class="o">,</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="bp">|</span><span class="n">s</span><span class="w"> </span><span class="n">n</span><span class="bp">|</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">cs</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="n">zero_lt_one</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">N</span><span class="o">,</span><span class="w"> </span><span class="n">h</span><span class="o">⟩</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">N</span><span class="o">,</span><span class="w"> </span><span class="bp">|</span><span class="n">a</span><span class="bp">|</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">exists_abs_le_of_convergesTo</span> <span class="o">{</span><span class="n">s</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">{</span><span class="n">a</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">cs</span> <span class="o">:</span> <span class="n">ConvergesTo</span> <span class="n">s</span> <span class="n">a</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">N</span> <span class="n">b</span><span class="o">,</span> <span class="bp">∀</span> <span class="n">n</span><span class="o">,</span> <span class="n">N</span> <span class="bp">≤</span> <span class="n">n</span> <span class="bp">→</span> <span class="bp">|</span><span class="n">s</span> <span class="n">n</span><span class="bp">|</span> <span class="bp"><</span> <span class="n">b</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rcases</span> <span class="n">cs</span> <span class="mi">1</span> <span class="n">zero_lt_one</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">N</span><span class="o">,</span> <span class="n">h</span><span class="o">⟩</span> <span class="n">use</span> <span class="n">N</span><span class="o">,</span> <span class="bp">|</span><span class="n">a</span><span class="bp">|</span> <span class="bp">+</span> <span class="mi">1</span> <span class="gr">sorry</span> </pre></div> </div> <p>In fact, the theorem could be strengthened to assert
-
@@ -1752,31 +1748,31 @@ To do so, we use the previous theorem to find a <code class="docutils literal nothat bounds <code class="docutils literal notranslate"><span class="pre">s</span></code> beyond some point <code class="docutils literal notranslate"><span class="pre">N₀</span></code>. See if you can understand the strategy we have outlined and finish the proof.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">aux</span><span class="w"> </span><span class="o">{</span><span class="n">s</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">cs</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ConvergesTo</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">ct</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ConvergesTo</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">ConvergesTo</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="n">εpos</span> <span class="w"> </span><span class="n">dsimp</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">exists_abs_le_of_convergesTo</span><span class="w"> </span><span class="n">cs</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">N₀</span><span class="o">,</span><span class="w"> </span><span class="n">B</span><span class="o">,</span><span class="w"> </span><span class="n">h₀</span><span class="o">⟩</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">Bpos</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">lt_of_le_of_lt</span><span class="w"> </span><span class="o">(</span><span class="n">abs_nonneg</span><span class="w"> </span><span class="n">_</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h₀</span><span class="w"> </span><span class="n">N₀</span><span class="w"> </span><span class="o">(</span><span class="n">le_refl</span><span class="w"> </span><span class="n">_</span><span class="o">))</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">pos₀</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">div_pos</span><span class="w"> </span><span class="n">εpos</span><span class="w"> </span><span class="n">Bpos</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">ct</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="n">pos₀</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">N₁</span><span class="o">,</span><span class="w"> </span><span class="n">h₁</span><span class="o">⟩</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">aux</span> <span class="o">{</span><span class="n">s</span> <span class="n">t</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">{</span><span class="n">a</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">cs</span> <span class="o">:</span> <span class="n">ConvergesTo</span> <span class="n">s</span> <span class="n">a</span><span class="o">)</span> <span class="o">(</span><span class="n">ct</span> <span class="o">:</span> <span class="n">ConvergesTo</span> <span class="n">t</span> <span class="mi">0</span><span class="o">)</span> <span class="o">:</span> <span class="n">ConvergesTo</span> <span class="o">(</span><span class="k">fun</span> <span class="n">n</span> <span class="bp">↦</span> <span class="n">s</span> <span class="n">n</span> <span class="bp">*</span> <span class="n">t</span> <span class="n">n</span><span class="o">)</span> <span class="mi">0</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">ε</span> <span class="n">εpos</span> <span class="n">dsimp</span> <span class="n">rcases</span> <span class="n">exists_abs_le_of_convergesTo</span> <span class="n">cs</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">N₀</span><span class="o">,</span> <span class="n">B</span><span class="o">,</span> <span class="n">h₀</span><span class="o">⟩</span> <span class="k">have</span> <span class="n">Bpos</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp"><</span> <span class="n">B</span> <span class="o">:=</span> <span class="n">lt_of_le_of_lt</span> <span class="o">(</span><span class="n">abs_nonneg</span> <span class="n">_</span><span class="o">)</span> <span class="o">(</span><span class="n">h₀</span> <span class="n">N₀</span> <span class="o">(</span><span class="n">le_refl</span> <span class="n">_</span><span class="o">))</span> <span class="k">have</span> <span class="n">pos₀</span> <span class="o">:</span> <span class="n">ε</span> <span class="bp">/</span> <span class="n">B</span> <span class="bp">></span> <span class="mi">0</span> <span class="o">:=</span> <span class="n">div_pos</span> <span class="n">εpos</span> <span class="n">Bpos</span> <span class="n">rcases</span> <span class="n">ct</span> <span class="n">_</span> <span class="n">pos₀</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">N₁</span><span class="o">,</span> <span class="n">h₁</span><span class="o">⟩</span> <span class="gr">sorry</span> </pre></div> </div> <p>If you have made it this far, congratulations! We are now within striking distance of our theorem. The following proof finishes it off.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">convergesTo_mul</span><span class="w"> </span><span class="o">{</span><span class="n">s</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span> <span class="w"> </span><span class="o">(</span><span class="n">cs</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ConvergesTo</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">ct</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ConvergesTo</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">ConvergesTo</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">h₁</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ConvergesTo</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">t</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="bp">-</span><span class="n">b</span><span class="o">))</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">aux</span><span class="w"> </span><span class="n">cs</span> <span class="w"> </span><span class="n">convert</span><span class="w"> </span><span class="n">convergesTo_add</span><span class="w"> </span><span class="n">ct</span><span class="w"> </span><span class="o">(</span><span class="n">convergesTo_const</span><span class="w"> </span><span class="o">(</span><span class="bp">-</span><span class="n">b</span><span class="o">))</span> <span class="w"> </span><span class="n">ring</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">convergesTo_add</span><span class="w"> </span><span class="n">h₁</span><span class="w"> </span><span class="o">(</span><span class="n">convergesTo_mul_const</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">cs</span><span class="o">)</span> <span class="w"> </span><span class="n">convert</span><span class="w"> </span><span class="n">convergesTo_add</span><span class="w"> </span><span class="n">h₁</span><span class="w"> </span><span class="o">(</span><span class="n">convergesTo_mul_const</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">cs</span><span class="o">)</span><span class="w"> </span><span class="n">using</span><span class="w"> </span><span class="mi">1</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">ext</span><span class="bp">;</span><span class="w"> </span><span class="n">ring</span> <span class="w"> </span><span class="n">ring</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">convergesTo_mul</span> <span class="o">{</span><span class="n">s</span> <span class="n">t</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">{</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">cs</span> <span class="o">:</span> <span class="n">ConvergesTo</span> <span class="n">s</span> <span class="n">a</span><span class="o">)</span> <span class="o">(</span><span class="n">ct</span> <span class="o">:</span> <span class="n">ConvergesTo</span> <span class="n">t</span> <span class="n">b</span><span class="o">)</span> <span class="o">:</span> <span class="n">ConvergesTo</span> <span class="o">(</span><span class="k">fun</span> <span class="n">n</span> <span class="bp">↦</span> <span class="n">s</span> <span class="n">n</span> <span class="bp">*</span> <span class="n">t</span> <span class="n">n</span><span class="o">)</span> <span class="o">(</span><span class="n">a</span> <span class="bp">*</span> <span class="n">b</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="k">have</span> <span class="n">h₁</span> <span class="o">:</span> <span class="n">ConvergesTo</span> <span class="o">(</span><span class="k">fun</span> <span class="n">n</span> <span class="bp">↦</span> <span class="n">s</span> <span class="n">n</span> <span class="bp">*</span> <span class="o">(</span><span class="n">t</span> <span class="n">n</span> <span class="bp">+</span> <span class="bp">-</span><span class="n">b</span><span class="o">))</span> <span class="mi">0</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">apply</span> <span class="n">aux</span> <span class="n">cs</span> <span class="n">convert</span> <span class="n">convergesTo_add</span> <span class="n">ct</span> <span class="o">(</span><span class="n">convergesTo_const</span> <span class="o">(</span><span class="bp">-</span><span class="n">b</span><span class="o">))</span> <span class="n">ring</span> <span class="k">have</span> <span class="o">:=</span> <span class="n">convergesTo_add</span> <span class="n">h₁</span> <span class="o">(</span><span class="n">convergesTo_mul_const</span> <span class="n">b</span> <span class="n">cs</span><span class="o">)</span> <span class="n">convert</span> <span class="n">convergesTo_add</span> <span class="n">h₁</span> <span class="o">(</span><span class="n">convergesTo_mul_const</span> <span class="n">b</span> <span class="n">cs</span><span class="o">)</span> <span class="n">using</span> <span class="mi">1</span> <span class="bp">·</span> <span class="n">ext</span><span class="bp">;</span> <span class="n">ring</span> <span class="n">ring</span> </pre></div> </div> <p>For another challenging exercise,
-
@@ -1784,22 +1780,22 @@ try filling out the following sketch of a proof that limitsare unique. (If you are feeling bold, you can delete the proof sketch and try proving it from scratch.)</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">convergesTo_unique</span><span class="w"> </span><span class="o">{</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span> <span class="w"> </span><span class="o">(</span><span class="n">sa</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ConvergesTo</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">sb</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ConvergesTo</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">by_contra</span><span class="w"> </span><span class="n">abne</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">|</span><span class="n">a</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">b</span><span class="bp">|</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="k">let</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="bp">|</span><span class="n">a</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">b</span><span class="bp">|</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">εpos</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">change</span><span class="w"> </span><span class="bp">|</span><span class="n">a</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">b</span><span class="bp">|</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span> <span class="w"> </span><span class="n">linarith</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">sa</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="n">εpos</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">Na</span><span class="o">,</span><span class="w"> </span><span class="n">hNa</span><span class="o">⟩</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">sb</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="n">εpos</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">Nb</span><span class="o">,</span><span class="w"> </span><span class="n">hNb</span><span class="o">⟩</span> <span class="w"> </span><span class="k">let</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">max</span><span class="w"> </span><span class="n">Na</span><span class="w"> </span><span class="n">Nb</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">absa</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">|</span><span class="n">s</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">a</span><span class="bp">|</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">absb</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">|</span><span class="n">s</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">b</span><span class="bp">|</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">|</span><span class="n">a</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">b</span><span class="bp">|</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="bp">|</span><span class="n">a</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">b</span><span class="bp">|</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">lt_irrefl</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="n">this</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">convergesTo_unique</span> <span class="o">{</span><span class="n">s</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">{</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">sa</span> <span class="o">:</span> <span class="n">ConvergesTo</span> <span class="n">s</span> <span class="n">a</span><span class="o">)</span> <span class="o">(</span><span class="n">sb</span> <span class="o">:</span> <span class="n">ConvergesTo</span> <span class="n">s</span> <span class="n">b</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">=</span> <span class="n">b</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">by_contra</span> <span class="n">abne</span> <span class="k">have</span> <span class="o">:</span> <span class="bp">|</span><span class="n">a</span> <span class="bp">-</span> <span class="n">b</span><span class="bp">|</span> <span class="bp">></span> <span class="mi">0</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="k">let</span> <span class="n">ε</span> <span class="o">:=</span> <span class="bp">|</span><span class="n">a</span> <span class="bp">-</span> <span class="n">b</span><span class="bp">|</span> <span class="bp">/</span> <span class="mi">2</span> <span class="k">have</span> <span class="n">εpos</span> <span class="o">:</span> <span class="n">ε</span> <span class="bp">></span> <span class="mi">0</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">change</span> <span class="bp">|</span><span class="n">a</span> <span class="bp">-</span> <span class="n">b</span><span class="bp">|</span> <span class="bp">/</span> <span class="mi">2</span> <span class="bp">></span> <span class="mi">0</span> <span class="n">linarith</span> <span class="n">rcases</span> <span class="n">sa</span> <span class="n">ε</span> <span class="n">εpos</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">Na</span><span class="o">,</span> <span class="n">hNa</span><span class="o">⟩</span> <span class="n">rcases</span> <span class="n">sb</span> <span class="n">ε</span> <span class="n">εpos</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">Nb</span><span class="o">,</span> <span class="n">hNb</span><span class="o">⟩</span> <span class="k">let</span> <span class="n">N</span> <span class="o">:=</span> <span class="n">max</span> <span class="n">Na</span> <span class="n">Nb</span> <span class="k">have</span> <span class="n">absa</span> <span class="o">:</span> <span class="bp">|</span><span class="n">s</span> <span class="n">N</span> <span class="bp">-</span> <span class="n">a</span><span class="bp">|</span> <span class="bp"><</span> <span class="n">ε</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="k">have</span> <span class="n">absb</span> <span class="o">:</span> <span class="bp">|</span><span class="n">s</span> <span class="n">N</span> <span class="bp">-</span> <span class="n">b</span><span class="bp">|</span> <span class="bp"><</span> <span class="n">ε</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="k">have</span> <span class="o">:</span> <span class="bp">|</span><span class="n">a</span> <span class="bp">-</span> <span class="n">b</span><span class="bp">|</span> <span class="bp"><</span> <span class="bp">|</span><span class="n">a</span> <span class="bp">-</span> <span class="n">b</span><span class="bp">|</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="n">exact</span> <span class="n">lt_irrefl</span> <span class="n">_</span> <span class="n">this</span> </pre></div> </div> <p>We close the section with the observation that our proofs can be generalized.
-
@@ -1808,10 +1804,10 @@ natural numbers is that their structure carries a partial orderwith <code class="docutils literal notranslate"><span class="pre">min</span></code> and <code class="docutils literal notranslate"><span class="pre">max</span></code>. You can check that everything still works if you replace <code class="docutils literal notranslate"><span class="pre">ℕ</span></code> everywhere by any linear order <code class="docutils literal notranslate"><span class="pre">α</span></code>:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">LinearOrder</span><span class="w"> </span><span class="n">α</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">LinearOrder</span> <span class="n">α</span><span class="o">]</span> <span class="kd">def</span><span class="w"> </span><span class="n">ConvergesTo'</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span><span class="o">,</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">N</span><span class="o">,</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">≥</span><span class="w"> </span><span class="n">N</span><span class="o">,</span><span class="w"> </span><span class="bp">|</span><span class="n">s</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">a</span><span class="bp">|</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span> <span class="kd">def</span> <span class="n">ConvergesTo'</span> <span class="o">(</span><span class="n">s</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:=</span> <span class="bp">∀</span> <span class="n">ε</span> <span class="bp">></span> <span class="mi">0</span><span class="o">,</span> <span class="bp">∃</span> <span class="n">N</span><span class="o">,</span> <span class="bp">∀</span> <span class="n">n</span> <span class="bp">≥</span> <span class="n">N</span><span class="o">,</span> <span class="bp">|</span><span class="n">s</span> <span class="n">n</span> <span class="bp">-</span> <span class="n">a</span><span class="bp">|</span> <span class="bp"><</span> <span class="n">ε</span> </pre></div> </div> <p>In <a class="reference internal" href="C10_Topology.html#filters"><span class="std std-numref">Section 10.1</span></a>, we will see that Mathlib has mechanisms
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@@ -1,24 +1,24 @@<!DOCTYPE html> <html class="writer-html5" lang="en" data-content_root="./"> <html class="writer-html5" lang="en" > <head> <meta charset="utf-8" /><meta name="viewport" content="width=device-width, initial-scale=1" /> <meta charset="utf-8" /><meta name="generator" content="Docutils 0.17.1: http://docutils.sourceforge.net/" /> <meta name="viewport" content="width=device-width, initial-scale=1.0" /> <title>4. Sets and Functions — Mathematics in Lean 0.1 documentation</title> <link rel="stylesheet" type="text/css" href="_static/pygments.css?v=80d5e7a1" /> <link rel="stylesheet" type="text/css" href="_static/css/theme.css?v=e59714d7" /> <link rel="stylesheet" type="text/css" href="_static/css/custom.css?v=0731ccc3" /> <link rel="stylesheet" href="_static/pygments.css" type="text/css" /> <link rel="stylesheet" href="_static/css/theme.css" type="text/css" /> <link rel="stylesheet" href="_static/css/custom.css" type="text/css" /> <link rel="shortcut icon" href="_static/favicon.ico"/> <script src="_static/jquery.js?v=5d32c60e"></script> <script src="_static/_sphinx_javascript_frameworks_compat.js?v=2cd50e6c"></script> <script src="_static/documentation_options.js?v=2709fde1"></script> <script src="_static/doctools.js?v=9bcbadda"></script> <script src="_static/sphinx_highlight.js?v=dc90522c"></script> <script async="async" src="https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js"></script> <!--[if lt IE 9]> <script src="_static/js/html5shiv.min.js"></script> <![endif]--> <script data-url_root="./" id="documentation_options" src="_static/documentation_options.js"></script> <script src="_static/jquery.js"></script> <script src="_static/underscore.js"></script> <script src="_static/_sphinx_javascript_frameworks_compat.js"></script> <script src="_static/doctools.js"></script> <script async="async" src="https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js"></script> <script src="_static/js/theme.js"></script> <link rel="index" title="Index" href="genindex.html" /> <link rel="search" title="Search" href="search.html" />
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@@ -31,15 +31,11 @@<nav data-toggle="wy-nav-shift" class="wy-nav-side"> <div class="wy-side-scroll"> <div class="wy-side-nav-search" > <a href="index.html" class="icon icon-home"> Mathematics in Lean <a href="index.html" class="icon icon-home"> Mathematics in Lean </a> <div role="search"> <form id="rtd-search-form" class="wy-form" action="search.html" method="get"> <input type="text" name="q" placeholder="Search docs" aria-label="Search docs" /> <input type="text" name="q" placeholder="Search docs" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form>
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@@ -81,8 +77,8 @@<div class="rst-content"> <div role="navigation" aria-label="Page navigation"> <ul class="wy-breadcrumbs"> <li><a href="index.html" class="icon icon-home" aria-label="Home"></a></li> <li class="breadcrumb-item active"><span class="section-number">4. </span>Sets and Functions</li> <li><a href="index.html" class="icon icon-home"></a> »</li> <li><span class="section-number">4. </span>Sets and Functions</li> <li class="wy-breadcrumbs-aside"> <a href="_sources/C04_Sets_and_Functions.rst.txt" rel="nofollow"> View page source</a> </li>
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@@ -93,7 +89,7 @@<div itemprop="articleBody"> <section id="sets-and-functions"> <span id="id1"></span><h1><span class="section-number">4. </span>Sets and Functions<a class="headerlink" href="#sets-and-functions" title="Link to this heading"></a></h1> <span id="id1"></span><h1><span class="section-number">4. </span>Sets and Functions<a class="headerlink" href="#sets-and-functions" title="Permalink to this heading"></a></h1> <p>The vocabulary of sets, relations, and functions provides a uniform language for carrying out constructions in all the branches of mathematics.
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@@ -126,7 +122,7 @@ from real numbers to real numbers.The distinction between types and sets takes some getting used to, but this chapter will take you through the essentials.</p> <section id="sets"> <span id="id2"></span><h2><span class="section-number">4.1. </span>Sets<a class="headerlink" href="#sets" title="Link to this heading"></a></h2> <span id="id2"></span><h2><span class="section-number">4.1. </span>Sets<a class="headerlink" href="#sets" title="Permalink to this heading"></a></h2> <p id="index-0">If <code class="docutils literal notranslate"><span class="pre">α</span></code> is any type, the type <code class="docutils literal notranslate"><span class="pre">Set</span> <span class="pre">α</span></code> consists of sets of elements of <code class="docutils literal notranslate"><span class="pre">α</span></code>. This type supports the usual set-theoretic operations and relations.
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@@ -155,69 +151,69 @@ Unlike <code class="docutils literal notranslate"><span class="pre">rw</span></cinside a universal or existential quantifier. If you step through the proof, you can see the effects of these commands.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">α</span><span class="o">)</span> <span class="kn">open</span><span class="w"> </span><span class="n">Set</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">t</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">subset_def</span><span class="o">,</span><span class="w"> </span><span class="n">inter_def</span><span class="o">,</span><span class="w"> </span><span class="n">inter_def</span><span class="o">]</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">subset_def</span><span class="o">]</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="n">only</span><span class="w"> </span><span class="o">[</span><span class="n">mem_setOf</span><span class="o">]</span> <span class="w"> </span><span class="n">rintro</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">⟨</span><span class="n">xs</span><span class="o">,</span><span class="w"> </span><span class="n">xu</span><span class="o">⟩</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="o">⟨</span><span class="n">h</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="n">xs</span><span class="o">,</span><span class="w"> </span><span class="n">xu</span><span class="o">⟩</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">t</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="n">only</span><span class="w"> </span><span class="o">[</span><span class="n">subset_def</span><span class="o">,</span><span class="w"> </span><span class="n">mem_inter_iff</span><span class="o">]</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="bp">*</span> <span class="w"> </span><span class="n">rintro</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">⟨</span><span class="n">xs</span><span class="o">,</span><span class="w"> </span><span class="n">xu</span><span class="o">⟩</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="o">⟨</span><span class="n">h</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="n">xs</span><span class="o">,</span><span class="w"> </span><span class="n">xu</span><span class="o">⟩</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">s</span> <span class="n">t</span> <span class="n">u</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">α</span><span class="o">)</span> <span class="kn">open</span> <span class="n">Set</span> <span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">s</span> <span class="bp">⊆</span> <span class="n">t</span><span class="o">)</span> <span class="o">:</span> <span class="n">s</span> <span class="bp">∩</span> <span class="n">u</span> <span class="bp">⊆</span> <span class="n">t</span> <span class="bp">∩</span> <span class="n">u</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">subset_def</span><span class="o">,</span> <span class="n">inter_def</span><span class="o">,</span> <span class="n">inter_def</span><span class="o">]</span> <span class="n">rw</span> <span class="o">[</span><span class="n">subset_def</span><span class="o">]</span> <span class="n">at</span> <span class="n">h</span> <span class="n">simp</span> <span class="n">only</span> <span class="o">[</span><span class="n">mem_setOf</span><span class="o">]</span> <span class="n">rintro</span> <span class="n">x</span> <span class="o">⟨</span><span class="n">xs</span><span class="o">,</span> <span class="n">xu</span><span class="o">⟩</span> <span class="n">exact</span> <span class="o">⟨</span><span class="n">h</span> <span class="n">_</span> <span class="n">xs</span><span class="o">,</span> <span class="n">xu</span><span class="o">⟩</span> <span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">s</span> <span class="bp">⊆</span> <span class="n">t</span><span class="o">)</span> <span class="o">:</span> <span class="n">s</span> <span class="bp">∩</span> <span class="n">u</span> <span class="bp">⊆</span> <span class="n">t</span> <span class="bp">∩</span> <span class="n">u</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> <span class="n">only</span> <span class="o">[</span><span class="n">subset_def</span><span class="o">,</span> <span class="n">mem_inter_iff</span><span class="o">]</span> <span class="n">at</span> <span class="bp">*</span> <span class="n">rintro</span> <span class="n">x</span> <span class="o">⟨</span><span class="n">xs</span><span class="o">,</span> <span class="n">xu</span><span class="o">⟩</span> <span class="n">exact</span> <span class="o">⟨</span><span class="n">h</span> <span class="n">_</span> <span class="n">xs</span><span class="o">,</span> <span class="n">xu</span><span class="o">⟩</span> </pre></div> </div> <p>In this example, we open the <code class="docutils literal notranslate"><span class="pre">set</span></code> namespace to have access to the shorter names for the theorems. But, in fact, we can delete the calls to <code class="docutils literal notranslate"><span class="pre">rw</span></code> and <code class="docutils literal notranslate"><span class="pre">simp</span></code> entirely:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">t</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">xsu</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="o">⟨</span><span class="n">h</span><span class="w"> </span><span class="n">xsu</span><span class="bp">.</span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="n">xsu</span><span class="bp">.</span><span class="mi">2</span><span class="o">⟩</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">s</span> <span class="bp">⊆</span> <span class="n">t</span><span class="o">)</span> <span class="o">:</span> <span class="n">s</span> <span class="bp">∩</span> <span class="n">u</span> <span class="bp">⊆</span> <span class="n">t</span> <span class="bp">∩</span> <span class="n">u</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">x</span> <span class="n">xsu</span> <span class="n">exact</span> <span class="o">⟨</span><span class="n">h</span> <span class="n">xsu.1</span><span class="o">,</span> <span class="n">xsu.2</span><span class="o">⟩</span> </pre></div> </div> <p>What is going on here is known as <em>definitional reduction</em>: to make sense of the <code class="docutils literal notranslate"><span class="pre">intro</span></code> command and the anonymous constructors Lean is forced to expand the definitions. The following example also illustrate the phenomenon:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">t</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">⟨</span><span class="n">xs</span><span class="o">,</span><span class="w"> </span><span class="n">xu</span><span class="o">⟩</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="o">⟨</span><span class="n">h</span><span class="w"> </span><span class="n">xs</span><span class="o">,</span><span class="w"> </span><span class="n">xu</span><span class="o">⟩</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">s</span> <span class="bp">⊆</span> <span class="n">t</span><span class="o">)</span> <span class="o">:</span> <span class="n">s</span> <span class="bp">∩</span> <span class="n">u</span> <span class="bp">⊆</span> <span class="n">t</span> <span class="bp">∩</span> <span class="n">u</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">x</span> <span class="o">⟨</span><span class="n">xs</span><span class="o">,</span> <span class="n">xu</span><span class="o">⟩</span> <span class="bp">↦</span> <span class="o">⟨</span><span class="n">h</span> <span class="n">xs</span><span class="o">,</span> <span class="n">xu</span><span class="o">⟩</span> </pre></div> </div> <p>To deal with unions, we can use <code class="docutils literal notranslate"><span class="pre">Set.union_def</span></code> and <code class="docutils literal notranslate"><span class="pre">Set.mem_union</span></code>. Since <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">∈</span> <span class="pre">s</span> <span class="pre">∪</span> <span class="pre">t</span></code> unfolds to <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">∈</span> <span class="pre">s</span> <span class="pre">∨</span> <span class="pre">x</span> <span class="pre">∈</span> <span class="pre">t</span></code>, we can also use the <code class="docutils literal notranslate"><span class="pre">cases</span></code> tactic to force a definitional reduction.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="o">(</span><span class="n">t</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">u</span><span class="o">)</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">hx</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">xs</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">hx</span><span class="bp">.</span><span class="mi">1</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">xtu</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">hx</span><span class="bp">.</span><span class="mi">2</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">xtu</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="n">xt</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">xu</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">left</span> <span class="w"> </span><span class="k">show</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">t</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="o">⟨</span><span class="n">xs</span><span class="o">,</span><span class="w"> </span><span class="n">xt</span><span class="o">⟩</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">right</span> <span class="w"> </span><span class="k">show</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">u</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="o">⟨</span><span class="n">xs</span><span class="o">,</span><span class="w"> </span><span class="n">xu</span><span class="o">⟩</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">s</span> <span class="bp">∩</span> <span class="o">(</span><span class="n">t</span> <span class="bp">∪</span> <span class="n">u</span><span class="o">)</span> <span class="bp">⊆</span> <span class="n">s</span> <span class="bp">∩</span> <span class="n">t</span> <span class="bp">∪</span> <span class="n">s</span> <span class="bp">∩</span> <span class="n">u</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">x</span> <span class="n">hx</span> <span class="k">have</span> <span class="n">xs</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">s</span> <span class="o">:=</span> <span class="n">hx.1</span> <span class="k">have</span> <span class="n">xtu</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">t</span> <span class="bp">∪</span> <span class="n">u</span> <span class="o">:=</span> <span class="n">hx.2</span> <span class="n">rcases</span> <span class="n">xtu</span> <span class="k">with</span> <span class="n">xt</span> <span class="bp">|</span> <span class="n">xu</span> <span class="bp">·</span> <span class="n">left</span> <span class="k">show</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">s</span> <span class="bp">∩</span> <span class="n">t</span> <span class="n">exact</span> <span class="o">⟨</span><span class="n">xs</span><span class="o">,</span> <span class="n">xt</span><span class="o">⟩</span> <span class="bp">·</span> <span class="n">right</span> <span class="k">show</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">s</span> <span class="bp">∩</span> <span class="n">u</span> <span class="n">exact</span> <span class="o">⟨</span><span class="n">xs</span><span class="o">,</span> <span class="n">xu</span><span class="o">⟩</span> </pre></div> </div> <p>Since intersection binds tighter than union, the use of parentheses in the expression <code class="docutils literal notranslate"><span class="pre">(s</span> <span class="pre">∩</span> <span class="pre">t)</span> <span class="pre">∪</span> <span class="pre">(s</span> <span class="pre">∩</span> <span class="pre">u)</span></code> is unnecessary, but they make the meaning of the expression clearer. The following is a shorter proof of the same fact:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="o">(</span><span class="n">t</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">u</span><span class="o">)</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rintro</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">⟨</span><span class="n">xs</span><span class="o">,</span><span class="w"> </span><span class="n">xt</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">xu</span><span class="o">⟩</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">left</span><span class="bp">;</span><span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="o">⟨</span><span class="n">xs</span><span class="o">,</span><span class="w"> </span><span class="n">xt</span><span class="o">⟩</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">right</span><span class="bp">;</span><span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="o">⟨</span><span class="n">xs</span><span class="o">,</span><span class="w"> </span><span class="n">xu</span><span class="o">⟩</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">s</span> <span class="bp">∩</span> <span class="o">(</span><span class="n">t</span> <span class="bp">∪</span> <span class="n">u</span><span class="o">)</span> <span class="bp">⊆</span> <span class="n">s</span> <span class="bp">∩</span> <span class="n">t</span> <span class="bp">∪</span> <span class="n">s</span> <span class="bp">∩</span> <span class="n">u</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rintro</span> <span class="n">x</span> <span class="o">⟨</span><span class="n">xs</span><span class="o">,</span> <span class="n">xt</span> <span class="bp">|</span> <span class="n">xu</span><span class="o">⟩</span> <span class="bp">·</span> <span class="n">left</span><span class="bp">;</span> <span class="n">exact</span> <span class="o">⟨</span><span class="n">xs</span><span class="o">,</span> <span class="n">xt</span><span class="o">⟩</span> <span class="bp">·</span> <span class="n">right</span><span class="bp">;</span> <span class="n">exact</span> <span class="o">⟨</span><span class="n">xs</span><span class="o">,</span> <span class="n">xu</span><span class="o">⟩</span> </pre></div> </div> <p>As an exercise, try proving the other inclusion:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="o">(</span><span class="n">t</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">u</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">s</span> <span class="bp">∩</span> <span class="n">t</span> <span class="bp">∪</span> <span class="n">s</span> <span class="bp">∩</span> <span class="n">u</span> <span class="bp">⊆</span> <span class="n">s</span> <span class="bp">∩</span> <span class="o">(</span><span class="n">t</span> <span class="bp">∪</span> <span class="n">u</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>It might help to know that when using <code class="docutils literal notranslate"><span class="pre">rintro</span></code>,
-
@@ -232,28 +228,28 @@ It can be rewritten manually using <code class="docutils literal notranslate"><sor <code class="docutils literal notranslate"><span class="pre">Set.mem_diff</span></code>, but the following two proofs of the same inclusion show how to avoid using them.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="bp">\</span><span class="w"> </span><span class="n">t</span><span class="o">)</span><span class="w"> </span><span class="bp">\</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">\</span><span class="w"> </span><span class="o">(</span><span class="n">t</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">u</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">xstu</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">xs</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">xstu</span><span class="bp">.</span><span class="mi">1</span><span class="bp">.</span><span class="mi">1</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">xnt</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∉</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">xstu</span><span class="bp">.</span><span class="mi">1</span><span class="bp">.</span><span class="mi">2</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">xnu</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∉</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">xstu</span><span class="bp">.</span><span class="mi">2</span> <span class="w"> </span><span class="n">constructor</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">xs</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">xtu</span> <span class="w"> </span><span class="c1">-- x ∈ t ∨ x ∈ u</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">xtu</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="n">xt</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">xu</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="k">show</span><span class="w"> </span><span class="n">False</span><span class="bp">;</span><span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">xnt</span><span class="w"> </span><span class="n">xt</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="k">show</span><span class="w"> </span><span class="n">False</span><span class="bp">;</span><span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">xnu</span><span class="w"> </span><span class="n">xu</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="bp">\</span><span class="w"> </span><span class="n">t</span><span class="o">)</span><span class="w"> </span><span class="bp">\</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">\</span><span class="w"> </span><span class="o">(</span><span class="n">t</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">u</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rintro</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">⟨⟨</span><span class="n">xs</span><span class="o">,</span><span class="w"> </span><span class="n">xnt</span><span class="o">⟩,</span><span class="w"> </span><span class="n">xnu</span><span class="o">⟩</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">xs</span> <span class="w"> </span><span class="n">rintro</span><span class="w"> </span><span class="o">(</span><span class="n">xt</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">xu</span><span class="o">)</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">contradiction</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="o">(</span><span class="n">s</span> <span class="bp">\</span> <span class="n">t</span><span class="o">)</span> <span class="bp">\</span> <span class="n">u</span> <span class="bp">⊆</span> <span class="n">s</span> <span class="bp">\</span> <span class="o">(</span><span class="n">t</span> <span class="bp">∪</span> <span class="n">u</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">x</span> <span class="n">xstu</span> <span class="k">have</span> <span class="n">xs</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">s</span> <span class="o">:=</span> <span class="n">xstu.1.1</span> <span class="k">have</span> <span class="n">xnt</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">∉</span> <span class="n">t</span> <span class="o">:=</span> <span class="n">xstu.1.2</span> <span class="k">have</span> <span class="n">xnu</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">∉</span> <span class="n">u</span> <span class="o">:=</span> <span class="n">xstu.2</span> <span class="n">constructor</span> <span class="bp">·</span> <span class="n">exact</span> <span class="n">xs</span> <span class="n">intro</span> <span class="n">xtu</span> <span class="c1">-- x ∈ t ∨ x ∈ u</span> <span class="n">rcases</span> <span class="n">xtu</span> <span class="k">with</span> <span class="n">xt</span> <span class="bp">|</span> <span class="n">xu</span> <span class="bp">·</span> <span class="k">show</span> <span class="n">False</span><span class="bp">;</span> <span class="n">exact</span> <span class="n">xnt</span> <span class="n">xt</span> <span class="bp">·</span> <span class="k">show</span> <span class="n">False</span><span class="bp">;</span> <span class="n">exact</span> <span class="n">xnu</span> <span class="n">xu</span> <span class="kd">example</span> <span class="o">:</span> <span class="o">(</span><span class="n">s</span> <span class="bp">\</span> <span class="n">t</span><span class="o">)</span> <span class="bp">\</span> <span class="n">u</span> <span class="bp">⊆</span> <span class="n">s</span> <span class="bp">\</span> <span class="o">(</span><span class="n">t</span> <span class="bp">∪</span> <span class="n">u</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rintro</span> <span class="n">x</span> <span class="o">⟨⟨</span><span class="n">xs</span><span class="o">,</span> <span class="n">xnt</span><span class="o">⟩,</span> <span class="n">xnu</span><span class="o">⟩</span> <span class="n">use</span> <span class="n">xs</span> <span class="n">rintro</span> <span class="o">(</span><span class="n">xt</span> <span class="bp">|</span> <span class="n">xu</span><span class="o">)</span> <span class="bp"><;></span> <span class="n">contradiction</span> </pre></div> </div> <p>As an exercise, prove the reverse inclusion:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">\</span><span class="w"> </span><span class="o">(</span><span class="n">t</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">u</span><span class="o">)</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="bp">\</span><span class="w"> </span><span class="n">t</span><span class="o">)</span><span class="w"> </span><span class="bp">\</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">s</span> <span class="bp">\</span> <span class="o">(</span><span class="n">t</span> <span class="bp">∪</span> <span class="n">u</span><span class="o">)</span> <span class="bp">⊆</span> <span class="o">(</span><span class="n">s</span> <span class="bp">\</span> <span class="n">t</span><span class="o">)</span> <span class="bp">\</span> <span class="n">u</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>To prove that two sets are equal,
-
@@ -262,57 +258,57 @@ of the other.This principle is known as “extensionality,” and, unsurprisingly, the <code class="docutils literal notranslate"><span class="pre">ext</span></code> tactic is equipped to handle it.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">ext</span><span class="w"> </span><span class="n">x</span> <span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="n">only</span><span class="w"> </span><span class="o">[</span><span class="n">mem_inter_iff</span><span class="o">]</span> <span class="w"> </span><span class="n">constructor</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">rintro</span><span class="w"> </span><span class="o">⟨</span><span class="n">xs</span><span class="o">,</span><span class="w"> </span><span class="n">xt</span><span class="o">⟩</span><span class="bp">;</span><span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="o">⟨</span><span class="n">xt</span><span class="o">,</span><span class="w"> </span><span class="n">xs</span><span class="o">⟩</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">rintro</span><span class="w"> </span><span class="o">⟨</span><span class="n">xt</span><span class="o">,</span><span class="w"> </span><span class="n">xs</span><span class="o">⟩</span><span class="bp">;</span><span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="o">⟨</span><span class="n">xs</span><span class="o">,</span><span class="w"> </span><span class="n">xt</span><span class="o">⟩</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">s</span> <span class="bp">∩</span> <span class="n">t</span> <span class="bp">=</span> <span class="n">t</span> <span class="bp">∩</span> <span class="n">s</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">ext</span> <span class="n">x</span> <span class="n">simp</span> <span class="n">only</span> <span class="o">[</span><span class="n">mem_inter_iff</span><span class="o">]</span> <span class="n">constructor</span> <span class="bp">·</span> <span class="n">rintro</span> <span class="o">⟨</span><span class="n">xs</span><span class="o">,</span> <span class="n">xt</span><span class="o">⟩</span><span class="bp">;</span> <span class="n">exact</span> <span class="o">⟨</span><span class="n">xt</span><span class="o">,</span> <span class="n">xs</span><span class="o">⟩</span> <span class="bp">·</span> <span class="n">rintro</span> <span class="o">⟨</span><span class="n">xt</span><span class="o">,</span> <span class="n">xs</span><span class="o">⟩</span><span class="bp">;</span> <span class="n">exact</span> <span class="o">⟨</span><span class="n">xs</span><span class="o">,</span> <span class="n">xt</span><span class="o">⟩</span> </pre></div> </div> <p>Once again, deleting the line <code class="docutils literal notranslate"><span class="pre">simp</span> <span class="pre">only</span> <span class="pre">[mem_inter_iff]</span></code> does not harm the proof. In fact, if you like inscrutable proof terms, the following one-line proof is for you:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Set.ext</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="o">⟨</span><span class="k">fun</span><span class="w"> </span><span class="o">⟨</span><span class="n">xs</span><span class="o">,</span><span class="w"> </span><span class="n">xt</span><span class="o">⟩</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="o">⟨</span><span class="n">xt</span><span class="o">,</span><span class="w"> </span><span class="n">xs</span><span class="o">⟩,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="o">⟨</span><span class="n">xt</span><span class="o">,</span><span class="w"> </span><span class="n">xs</span><span class="o">⟩</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="o">⟨</span><span class="n">xs</span><span class="o">,</span><span class="w"> </span><span class="n">xt</span><span class="o">⟩⟩</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">s</span> <span class="bp">∩</span> <span class="n">t</span> <span class="bp">=</span> <span class="n">t</span> <span class="bp">∩</span> <span class="n">s</span> <span class="o">:=</span> <span class="n">Set.ext</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="o">⟨</span><span class="k">fun</span> <span class="o">⟨</span><span class="n">xs</span><span class="o">,</span> <span class="n">xt</span><span class="o">⟩</span> <span class="bp">↦</span> <span class="o">⟨</span><span class="n">xt</span><span class="o">,</span> <span class="n">xs</span><span class="o">⟩,</span> <span class="k">fun</span> <span class="o">⟨</span><span class="n">xt</span><span class="o">,</span> <span class="n">xs</span><span class="o">⟩</span> <span class="bp">↦</span> <span class="o">⟨</span><span class="n">xs</span><span class="o">,</span> <span class="n">xt</span><span class="o">⟩⟩</span> </pre></div> </div> <p>Here is an even shorter proof, using the simplifier:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">ext</span><span class="w"> </span><span class="n">x</span><span class="bp">;</span><span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="o">[</span><span class="n">and_comm</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">s</span> <span class="bp">∩</span> <span class="n">t</span> <span class="bp">=</span> <span class="n">t</span> <span class="bp">∩</span> <span class="n">s</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">ext</span> <span class="n">x</span><span class="bp">;</span> <span class="n">simp</span> <span class="o">[</span><span class="n">and_comm</span><span class="o">]</span> </pre></div> </div> <p>An alternative to using <code class="docutils literal notranslate"><span class="pre">ext</span></code> is to use the theorem <code class="docutils literal notranslate"><span class="pre">Subset.antisymm</span></code> which allows us to prove an equation <code class="docutils literal notranslate"><span class="pre">s</span> <span class="pre">=</span> <span class="pre">t</span></code> between sets by proving <code class="docutils literal notranslate"><span class="pre">s</span> <span class="pre">⊆</span> <span class="pre">t</span></code> and <code class="docutils literal notranslate"><span class="pre">t</span> <span class="pre">⊆</span> <span class="pre">s</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">Subset.antisymm</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">rintro</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">⟨</span><span class="n">xs</span><span class="o">,</span><span class="w"> </span><span class="n">xt</span><span class="o">⟩</span><span class="bp">;</span><span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="o">⟨</span><span class="n">xt</span><span class="o">,</span><span class="w"> </span><span class="n">xs</span><span class="o">⟩</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">rintro</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">⟨</span><span class="n">xt</span><span class="o">,</span><span class="w"> </span><span class="n">xs</span><span class="o">⟩</span><span class="bp">;</span><span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="o">⟨</span><span class="n">xs</span><span class="o">,</span><span class="w"> </span><span class="n">xt</span><span class="o">⟩</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">s</span> <span class="bp">∩</span> <span class="n">t</span> <span class="bp">=</span> <span class="n">t</span> <span class="bp">∩</span> <span class="n">s</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">apply</span> <span class="n">Subset.antisymm</span> <span class="bp">·</span> <span class="n">rintro</span> <span class="n">x</span> <span class="o">⟨</span><span class="n">xs</span><span class="o">,</span> <span class="n">xt</span><span class="o">⟩</span><span class="bp">;</span> <span class="n">exact</span> <span class="o">⟨</span><span class="n">xt</span><span class="o">,</span> <span class="n">xs</span><span class="o">⟩</span> <span class="bp">·</span> <span class="n">rintro</span> <span class="n">x</span> <span class="o">⟨</span><span class="n">xt</span><span class="o">,</span> <span class="n">xs</span><span class="o">⟩</span><span class="bp">;</span> <span class="n">exact</span> <span class="o">⟨</span><span class="n">xs</span><span class="o">,</span> <span class="n">xt</span><span class="o">⟩</span> </pre></div> </div> <p>Try finishing this proof term:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Subset.antisymm</span><span class="w"> </span><span class="gr">sorry</span><span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">s</span> <span class="bp">∩</span> <span class="n">t</span> <span class="bp">=</span> <span class="n">t</span> <span class="bp">∩</span> <span class="n">s</span> <span class="o">:=</span> <span class="n">Subset.antisymm</span> <span class="gr">sorry</span> <span class="gr">sorry</span> </pre></div> </div> <p>Remember that you can replace <cite>sorry</cite> by an underscore, and when you hover over it, Lean will show you what it expects at that point.</p> <p>Here are some set-theoretic identities you might enjoy proving:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">t</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">s</span> <span class="bp">∩</span> <span class="o">(</span><span class="n">s</span> <span class="bp">∪</span> <span class="n">t</span><span class="o">)</span> <span class="bp">=</span> <span class="n">s</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">s</span> <span class="bp">∪</span> <span class="n">s</span> <span class="bp">∩</span> <span class="n">t</span> <span class="bp">=</span> <span class="n">s</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">\</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">s</span> <span class="bp">\</span> <span class="n">t</span> <span class="bp">∪</span> <span class="n">t</span> <span class="bp">=</span> <span class="n">s</span> <span class="bp">∪</span> <span class="n">t</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">\</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">\</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">t</span><span class="o">)</span><span class="w"> </span><span class="bp">\</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">t</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">s</span> <span class="bp">\</span> <span class="n">t</span> <span class="bp">∪</span> <span class="n">t</span> <span class="bp">\</span> <span class="n">s</span> <span class="bp">=</span> <span class="o">(</span><span class="n">s</span> <span class="bp">∪</span> <span class="n">t</span><span class="o">)</span> <span class="bp">\</span> <span class="o">(</span><span class="n">s</span> <span class="bp">∩</span> <span class="n">t</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>When it comes to representing sets,
-
@@ -328,17 +324,17 @@ In other words, sets are really properties, treated as objects.</p>The expression <code class="docutils literal notranslate"><span class="pre">{</span> <span class="pre">y</span> <span class="pre">|</span> <span class="pre">P</span> <span class="pre">y</span> <span class="pre">}</span></code> unfolds to <code class="docutils literal notranslate"><span class="pre">(fun</span> <span class="pre">y</span> <span class="pre">↦</span> <span class="pre">P</span> <span class="pre">y)</span></code>, so <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">∈</span> <span class="pre">{</span> <span class="pre">y</span> <span class="pre">|</span> <span class="pre">P</span> <span class="pre">y</span> <span class="pre">}</span></code> reduces to <code class="docutils literal notranslate"><span class="pre">P</span> <span class="pre">x</span></code>. So we can turn the property of being even into the set of even numbers:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">evens</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">Even</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">}</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">evens</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">ℕ</span> <span class="o">:=</span> <span class="o">{</span> <span class="n">n</span> <span class="bp">|</span> <span class="n">Even</span> <span class="n">n</span> <span class="o">}</span> <span class="kd">def</span><span class="w"> </span><span class="n">odds</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="bp">¬</span><span class="n">Even</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">}</span> <span class="kd">def</span> <span class="n">odds</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">ℕ</span> <span class="o">:=</span> <span class="o">{</span> <span class="n">n</span> <span class="bp">|</span> <span class="bp">¬</span><span class="n">Even</span> <span class="n">n</span> <span class="o">}</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">evens</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">odds</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">univ</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">evens</span><span class="o">,</span><span class="w"> </span><span class="n">odds</span><span class="o">]</span> <span class="w"> </span><span class="n">ext</span><span class="w"> </span><span class="n">n</span> <span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="o">[</span><span class="bp">-</span><span class="n">Nat.not_even_iff_odd</span><span class="o">]</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">Classical.em</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">evens</span> <span class="bp">∪</span> <span class="n">odds</span> <span class="bp">=</span> <span class="n">univ</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">evens</span><span class="o">,</span> <span class="n">odds</span><span class="o">]</span> <span class="n">ext</span> <span class="n">n</span> <span class="n">simp</span> <span class="o">[</span><span class="bp">-</span><span class="n">Nat.not_even_iff_odd</span><span class="o">]</span> <span class="n">apply</span> <span class="n">Classical.em</span> </pre></div> </div> <p>You should step through this proof and make sure
-
@@ -361,11 +357,11 @@ because Lean has trouble guessing which ones we mean.The following examples show how Lean unfolds the last two definitions when needed. In the second one, <code class="docutils literal notranslate"><span class="pre">trivial</span></code> is the canonical proof of <code class="docutils literal notranslate"><span class="pre">True</span></code> in the library.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="o">(</span><span class="bp">∅</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">ℕ</span><span class="o">))</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">False</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">h</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">∈</span> <span class="o">(</span><span class="bp">∅</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">ℕ</span><span class="o">))</span> <span class="o">:</span> <span class="n">False</span> <span class="o">:=</span> <span class="n">h</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="o">(</span><span class="n">univ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">trivial</span> <span class="kd">example</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">∈</span> <span class="o">(</span><span class="n">univ</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">:=</span> <span class="n">trivial</span> </pre></div> </div> <p>As an exercise, prove the following inclusion.
-
@@ -374,8 +370,8 @@ and use the simplifier to reduce theset-theoretic constructions to logic. We also recommend using the theorems <code class="docutils literal notranslate"><span class="pre">Nat.Prime.eq_two_or_odd</span></code> and <code class="docutils literal notranslate"><span class="pre">Nat.odd_iff</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">Nat.Prime</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">}</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">}</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="bp">¬</span><span class="n">Even</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">}</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="o">{</span> <span class="n">n</span> <span class="bp">|</span> <span class="n">Nat.Prime</span> <span class="n">n</span> <span class="o">}</span> <span class="bp">∩</span> <span class="o">{</span> <span class="n">n</span> <span class="bp">|</span> <span class="n">n</span> <span class="bp">></span> <span class="mi">2</span> <span class="o">}</span> <span class="bp">⊆</span> <span class="o">{</span> <span class="n">n</span> <span class="bp">|</span> <span class="bp">¬</span><span class="n">Even</span> <span class="n">n</span> <span class="o">}</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>Be careful: it is somewhat confusing that the library has multiple versions
-
@@ -384,21 +380,21 @@ The most general one makes sense in any commutative monoid with a zero element.The predicate <code class="docutils literal notranslate"><span class="pre">Nat.Prime</span></code> is specific to the natural numbers. Fortunately, there is a theorem that says that in the specific case, the two notions agree, so you can always rewrite one to the other.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#print</span><span class="w"> </span><span class="n">Prime</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#print</span> <span class="n">Prime</span> <span class="k">#print</span><span class="w"> </span><span class="n">Nat.Prime</span> <span class="k">#print</span> <span class="n">Nat.Prime</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Prime</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">Nat.Prime</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Nat.prime_iff.symm</span> <span class="kd">example</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">:</span> <span class="n">Prime</span> <span class="n">n</span> <span class="bp">↔</span> <span class="n">Nat.Prime</span> <span class="n">n</span> <span class="o">:=</span> <span class="n">Nat.prime_iff.symm</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Prime</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat.Prime</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">Nat.prime_iff</span><span class="o">]</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">h</span> <span class="kd">example</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">Prime</span> <span class="n">n</span><span class="o">)</span> <span class="o">:</span> <span class="n">Nat.Prime</span> <span class="n">n</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">Nat.prime_iff</span><span class="o">]</span> <span class="n">exact</span> <span class="n">h</span> </pre></div> </div> <p id="index-2">The <cite>rwa</cite> tactic follows a rewrite with the assumption tactic.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Prime</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat.Prime</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rwa</span><span class="w"> </span><span class="o">[</span><span class="n">Nat.prime_iff</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">Prime</span> <span class="n">n</span><span class="o">)</span> <span class="o">:</span> <span class="n">Nat.Prime</span> <span class="n">n</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rwa</span> <span class="o">[</span><span class="n">Nat.prime_iff</span><span class="o">]</span> </pre></div> </div> <p id="index-3">Lean introduces the notation <code class="docutils literal notranslate"><span class="pre">∀</span> <span class="pre">x</span> <span class="pre">∈</span> <span class="pre">s,</span> <span class="pre">...</span></code>,
-
@@ -419,28 +415,28 @@ these two expressions behave roughly the same.As a result, we usually don’t need to use <code class="docutils literal notranslate"><span class="pre">bex_def</span></code> to transform them explicitly. Here is are some examples of how they are used:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">(</span><span class="n">s</span> <span class="n">t</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">ℕ</span><span class="o">)</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h₀</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="bp">¬</span><span class="n">Even</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h₁</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="n">Prime</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="bp">¬</span><span class="n">Even</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">Prime</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">xs</span> <span class="w"> </span><span class="n">constructor</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">h₀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">xs</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">h₁</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">xs</span> <span class="kd">example</span> <span class="o">(</span><span class="n">h₀</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">s</span><span class="o">,</span> <span class="bp">¬</span><span class="n">Even</span> <span class="n">x</span><span class="o">)</span> <span class="o">(</span><span class="n">h₁</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">s</span><span class="o">,</span> <span class="n">Prime</span> <span class="n">x</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">s</span><span class="o">,</span> <span class="bp">¬</span><span class="n">Even</span> <span class="n">x</span> <span class="bp">∧</span> <span class="n">Prime</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">x</span> <span class="n">xs</span> <span class="n">constructor</span> <span class="bp">·</span> <span class="n">apply</span> <span class="n">h₀</span> <span class="n">x</span> <span class="n">xs</span> <span class="n">apply</span> <span class="n">h₁</span> <span class="n">x</span> <span class="n">xs</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="bp">¬</span><span class="n">Even</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">Prime</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="n">Prime</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">xs</span><span class="o">,</span><span class="w"> </span><span class="n">_</span><span class="o">,</span><span class="w"> </span><span class="n">prime_x</span><span class="o">⟩</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">xs</span> <span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">s</span><span class="o">,</span> <span class="bp">¬</span><span class="n">Even</span> <span class="n">x</span> <span class="bp">∧</span> <span class="n">Prime</span> <span class="n">x</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">s</span><span class="o">,</span> <span class="n">Prime</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rcases</span> <span class="n">h</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">x</span><span class="o">,</span> <span class="n">xs</span><span class="o">,</span> <span class="n">_</span><span class="o">,</span> <span class="n">prime_x</span><span class="o">⟩</span> <span class="n">use</span> <span class="n">x</span><span class="o">,</span> <span class="n">xs</span> </pre></div> </div> <p>See if you can prove these slight variations:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">section</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">ssubt</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">t</span><span class="o">)</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">ssubt</span> <span class="o">:</span> <span class="n">s</span> <span class="bp">⊆</span> <span class="n">t</span><span class="o">)</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h₀</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">t</span><span class="o">,</span><span class="w"> </span><span class="bp">¬</span><span class="n">Even</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h₁</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">t</span><span class="o">,</span><span class="w"> </span><span class="n">Prime</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="bp">¬</span><span class="n">Even</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">Prime</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">h₀</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">t</span><span class="o">,</span> <span class="bp">¬</span><span class="n">Even</span> <span class="n">x</span><span class="o">)</span> <span class="o">(</span><span class="n">h₁</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">t</span><span class="o">,</span> <span class="n">Prime</span> <span class="n">x</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">s</span><span class="o">,</span> <span class="bp">¬</span><span class="n">Even</span> <span class="n">x</span> <span class="bp">∧</span> <span class="n">Prime</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="bp">¬</span><span class="n">Even</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">Prime</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">t</span><span class="o">,</span><span class="w"> </span><span class="n">Prime</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">s</span><span class="o">,</span> <span class="bp">¬</span><span class="n">Even</span> <span class="n">x</span> <span class="bp">∧</span> <span class="n">Prime</span> <span class="n">x</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">t</span><span class="o">,</span> <span class="n">Prime</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">end</span> </pre></div>
-
@@ -456,35 +452,35 @@ There is nothing special about the natural numbers here,so <code class="docutils literal notranslate"><span class="pre">ℕ</span></code> can be replaced by any type <code class="docutils literal notranslate"><span class="pre">I</span></code> used to index the sets. The following illustrates their use.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">A</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">α</span><span class="o">)</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">α</span><span class="o">)</span> <span class="kn">open</span><span class="w"> </span><span class="n">Set</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="bp">⋃</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">⋃</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">ext</span><span class="w"> </span><span class="n">x</span> <span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="n">only</span><span class="w"> </span><span class="o">[</span><span class="n">mem_inter_iff</span><span class="o">,</span><span class="w"> </span><span class="n">mem_iUnion</span><span class="o">]</span> <span class="w"> </span><span class="n">constructor</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">rintro</span><span class="w"> </span><span class="o">⟨</span><span class="n">xs</span><span class="o">,</span><span class="w"> </span><span class="o">⟨</span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">xAi</span><span class="o">⟩⟩</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="o">⟨</span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">xAi</span><span class="o">,</span><span class="w"> </span><span class="n">xs</span><span class="o">⟩</span> <span class="w"> </span><span class="n">rintro</span><span class="w"> </span><span class="o">⟨</span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">xAi</span><span class="o">,</span><span class="w"> </span><span class="n">xs</span><span class="o">⟩</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="o">⟨</span><span class="n">xs</span><span class="o">,</span><span class="w"> </span><span class="o">⟨</span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">xAi</span><span class="o">⟩⟩</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="bp">⋂</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">(</span><span class="bp">⋂</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="bp">⋂</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">ext</span><span class="w"> </span><span class="n">x</span> <span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="n">only</span><span class="w"> </span><span class="o">[</span><span class="n">mem_inter_iff</span><span class="o">,</span><span class="w"> </span><span class="n">mem_iInter</span><span class="o">]</span> <span class="w"> </span><span class="n">constructor</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="n">constructor</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">i</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="bp">.</span><span class="mi">1</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">i</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="bp">.</span><span class="mi">2</span> <span class="w"> </span><span class="n">rintro</span><span class="w"> </span><span class="o">⟨</span><span class="n">h1</span><span class="o">,</span><span class="w"> </span><span class="n">h2</span><span class="o">⟩</span><span class="w"> </span><span class="n">i</span> <span class="w"> </span><span class="n">constructor</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">h1</span><span class="w"> </span><span class="n">i</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">h2</span><span class="w"> </span><span class="n">i</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">α</span> <span class="n">I</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">A</span> <span class="n">B</span> <span class="o">:</span> <span class="n">I</span> <span class="bp">→</span> <span class="n">Set</span> <span class="n">α</span><span class="o">)</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">s</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">α</span><span class="o">)</span> <span class="kn">open</span> <span class="n">Set</span> <span class="kd">example</span> <span class="o">:</span> <span class="o">(</span><span class="n">s</span> <span class="bp">∩</span> <span class="bp">⋃</span> <span class="n">i</span><span class="o">,</span> <span class="n">A</span> <span class="n">i</span><span class="o">)</span> <span class="bp">=</span> <span class="bp">⋃</span> <span class="n">i</span><span class="o">,</span> <span class="n">A</span> <span class="n">i</span> <span class="bp">∩</span> <span class="n">s</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">ext</span> <span class="n">x</span> <span class="n">simp</span> <span class="n">only</span> <span class="o">[</span><span class="n">mem_inter_iff</span><span class="o">,</span> <span class="n">mem_iUnion</span><span class="o">]</span> <span class="n">constructor</span> <span class="bp">·</span> <span class="n">rintro</span> <span class="o">⟨</span><span class="n">xs</span><span class="o">,</span> <span class="o">⟨</span><span class="n">i</span><span class="o">,</span> <span class="n">xAi</span><span class="o">⟩⟩</span> <span class="n">exact</span> <span class="o">⟨</span><span class="n">i</span><span class="o">,</span> <span class="n">xAi</span><span class="o">,</span> <span class="n">xs</span><span class="o">⟩</span> <span class="n">rintro</span> <span class="o">⟨</span><span class="n">i</span><span class="o">,</span> <span class="n">xAi</span><span class="o">,</span> <span class="n">xs</span><span class="o">⟩</span> <span class="n">exact</span> <span class="o">⟨</span><span class="n">xs</span><span class="o">,</span> <span class="o">⟨</span><span class="n">i</span><span class="o">,</span> <span class="n">xAi</span><span class="o">⟩⟩</span> <span class="kd">example</span> <span class="o">:</span> <span class="o">(</span><span class="bp">⋂</span> <span class="n">i</span><span class="o">,</span> <span class="n">A</span> <span class="n">i</span> <span class="bp">∩</span> <span class="n">B</span> <span class="n">i</span><span class="o">)</span> <span class="bp">=</span> <span class="o">(</span><span class="bp">⋂</span> <span class="n">i</span><span class="o">,</span> <span class="n">A</span> <span class="n">i</span><span class="o">)</span> <span class="bp">∩</span> <span class="bp">⋂</span> <span class="n">i</span><span class="o">,</span> <span class="n">B</span> <span class="n">i</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">ext</span> <span class="n">x</span> <span class="n">simp</span> <span class="n">only</span> <span class="o">[</span><span class="n">mem_inter_iff</span><span class="o">,</span> <span class="n">mem_iInter</span><span class="o">]</span> <span class="n">constructor</span> <span class="bp">·</span> <span class="n">intro</span> <span class="n">h</span> <span class="n">constructor</span> <span class="bp">·</span> <span class="n">intro</span> <span class="n">i</span> <span class="n">exact</span> <span class="o">(</span><span class="n">h</span> <span class="n">i</span><span class="o">)</span><span class="bp">.</span><span class="mi">1</span> <span class="n">intro</span> <span class="n">i</span> <span class="n">exact</span> <span class="o">(</span><span class="n">h</span> <span class="n">i</span><span class="o">)</span><span class="bp">.</span><span class="mi">2</span> <span class="n">rintro</span> <span class="o">⟨</span><span class="n">h1</span><span class="o">,</span> <span class="n">h2</span><span class="o">⟩</span> <span class="n">i</span> <span class="n">constructor</span> <span class="bp">·</span> <span class="n">exact</span> <span class="n">h1</span> <span class="n">i</span> <span class="n">exact</span> <span class="n">h2</span> <span class="n">i</span> </pre></div> </div> <p>Parentheses are often needed with an
-
@@ -495,8 +491,8 @@ the scope of the bound variable extends as far as it can.</p>One direction requires classical logic! We recommend using <code class="docutils literal notranslate"><span class="pre">by_cases</span> <span class="pre">xs</span> <span class="pre">:</span> <span class="pre">x</span> <span class="pre">∈</span> <span class="pre">s</span></code> at an appropriate point in the proof.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="bp">⋂</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">⋂</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="o">(</span><span class="n">s</span> <span class="bp">∪</span> <span class="bp">⋂</span> <span class="n">i</span><span class="o">,</span> <span class="n">A</span> <span class="n">i</span><span class="o">)</span> <span class="bp">=</span> <span class="bp">⋂</span> <span class="n">i</span><span class="o">,</span> <span class="n">A</span> <span class="n">i</span> <span class="bp">∪</span> <span class="n">s</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>Mathlib also has bounded unions and intersections,
-
@@ -505,23 +501,23 @@ You can unpack their meaning with <code class="docutils literal notranslate"><spand <code class="docutils literal notranslate"><span class="pre">mem_iInter₂</span></code>. As the following examples show, Lean’s simplifier carries out these replacements as well.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">primes</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">Nat.Prime</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">}</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="bp">⋃</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">primes</span><span class="o">,</span><span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">})</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">primes</span><span class="o">,</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">}</span><span class="w"> </span><span class="o">:=</span><span class="kd">by</span> <span class="w"> </span><span class="n">ext</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">mem_iUnion₂</span><span class="o">]</span> <span class="w"> </span><span class="n">simp</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="bp">⋃</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">primes</span><span class="o">,</span><span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">})</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">primes</span><span class="o">,</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">}</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">ext</span> <span class="w"> </span><span class="n">simp</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="bp">⋂</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">primes</span><span class="o">,</span><span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="bp">¬</span><span class="n">p</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">})</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">}</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">x</span> <span class="w"> </span><span class="n">contrapose</span><span class="bp">!</span> <span class="w"> </span><span class="n">simp</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">Nat.exists_prime_and_dvd</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">primes</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">ℕ</span> <span class="o">:=</span> <span class="o">{</span> <span class="n">x</span> <span class="bp">|</span> <span class="n">Nat.Prime</span> <span class="n">x</span> <span class="o">}</span> <span class="kd">example</span> <span class="o">:</span> <span class="o">(</span><span class="bp">⋃</span> <span class="n">p</span> <span class="bp">∈</span> <span class="n">primes</span><span class="o">,</span> <span class="o">{</span> <span class="n">x</span> <span class="bp">|</span> <span class="n">p</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">∣</span> <span class="n">x</span> <span class="o">})</span> <span class="bp">=</span> <span class="o">{</span> <span class="n">x</span> <span class="bp">|</span> <span class="bp">∃</span> <span class="n">p</span> <span class="bp">∈</span> <span class="n">primes</span><span class="o">,</span> <span class="n">p</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">∣</span> <span class="n">x</span> <span class="o">}</span> <span class="o">:=</span><span class="kd">by</span> <span class="n">ext</span> <span class="n">rw</span> <span class="o">[</span><span class="n">mem_iUnion₂</span><span class="o">]</span> <span class="n">simp</span> <span class="kd">example</span> <span class="o">:</span> <span class="o">(</span><span class="bp">⋃</span> <span class="n">p</span> <span class="bp">∈</span> <span class="n">primes</span><span class="o">,</span> <span class="o">{</span> <span class="n">x</span> <span class="bp">|</span> <span class="n">p</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">∣</span> <span class="n">x</span> <span class="o">})</span> <span class="bp">=</span> <span class="o">{</span> <span class="n">x</span> <span class="bp">|</span> <span class="bp">∃</span> <span class="n">p</span> <span class="bp">∈</span> <span class="n">primes</span><span class="o">,</span> <span class="n">p</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">∣</span> <span class="n">x</span> <span class="o">}</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">ext</span> <span class="n">simp</span> <span class="kd">example</span> <span class="o">:</span> <span class="o">(</span><span class="bp">⋂</span> <span class="n">p</span> <span class="bp">∈</span> <span class="n">primes</span><span class="o">,</span> <span class="o">{</span> <span class="n">x</span> <span class="bp">|</span> <span class="bp">¬</span><span class="n">p</span> <span class="bp">∣</span> <span class="n">x</span> <span class="o">})</span> <span class="bp">⊆</span> <span class="o">{</span> <span class="n">x</span> <span class="bp">|</span> <span class="n">x</span> <span class="bp">=</span> <span class="mi">1</span> <span class="o">}</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">x</span> <span class="n">contrapose</span><span class="bp">!</span> <span class="n">simp</span> <span class="n">apply</span> <span class="n">Nat.exists_prime_and_dvd</span> </pre></div> </div> <p>Try solving the following example, which is similar.
-
@@ -529,8 +525,8 @@ If you start typing <code class="docutils literal notranslate"><span class="pre"tab completion will tell you that <code class="docutils literal notranslate"><span class="pre">apply</span> <span class="pre">eq_univ_of_forall</span></code> is a good way to start the proof. We also recommend using the theorem <code class="docutils literal notranslate"><span class="pre">Nat.exists_infinite_primes</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="bp">⋃</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">primes</span><span class="o">,</span><span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="o">})</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">univ</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="o">(</span><span class="bp">⋃</span> <span class="n">p</span> <span class="bp">∈</span> <span class="n">primes</span><span class="o">,</span> <span class="o">{</span> <span class="n">x</span> <span class="bp">|</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">p</span> <span class="o">})</span> <span class="bp">=</span> <span class="n">univ</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>Give a collection of sets, <code class="docutils literal notranslate"><span class="pre">s</span> <span class="pre">:</span> <span class="pre">Set</span> <span class="pre">(Set</span> <span class="pre">α)</span></code>,
-
@@ -541,41 +537,41 @@ Similarly, their intersection, <code class="docutils literal notranslate"><spanThese operations are called <code class="docutils literal notranslate"><span class="pre">sUnion</span></code> and <code class="docutils literal notranslate"><span class="pre">sInter</span></code>, respectively. The following examples show their relationship to bounded union and intersection.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="o">(</span><span class="n">Set</span><span class="w"> </span><span class="n">α</span><span class="o">))</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">(</span><span class="n">s</span> <span class="o">:</span> <span class="n">Set</span> <span class="o">(</span><span class="n">Set</span> <span class="n">α</span><span class="o">))</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">⋃₀</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">⋃</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">ext</span><span class="w"> </span><span class="n">x</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">mem_iUnion₂</span><span class="o">]</span> <span class="w"> </span><span class="n">simp</span> <span class="kd">example</span> <span class="o">:</span> <span class="bp">⋃₀</span> <span class="n">s</span> <span class="bp">=</span> <span class="bp">⋃</span> <span class="n">t</span> <span class="bp">∈</span> <span class="n">s</span><span class="o">,</span> <span class="n">t</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">ext</span> <span class="n">x</span> <span class="n">rw</span> <span class="o">[</span><span class="n">mem_iUnion₂</span><span class="o">]</span> <span class="n">simp</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">⋂₀</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">⋂</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">ext</span><span class="w"> </span><span class="n">x</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">mem_iInter₂</span><span class="o">]</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">example</span> <span class="o">:</span> <span class="bp">⋂₀</span> <span class="n">s</span> <span class="bp">=</span> <span class="bp">⋂</span> <span class="n">t</span> <span class="bp">∈</span> <span class="n">s</span><span class="o">,</span> <span class="n">t</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">ext</span> <span class="n">x</span> <span class="n">rw</span> <span class="o">[</span><span class="n">mem_iInter₂</span><span class="o">]</span> <span class="n">rfl</span> </pre></div> </div> <p>In the library, these identities are called <code class="docutils literal notranslate"><span class="pre">sUnion_eq_biUnion</span></code> and <code class="docutils literal notranslate"><span class="pre">sInter_eq_biInter</span></code>.</p> </section> <section id="functions"> <span id="id3"></span><h2><span class="section-number">4.2. </span>Functions<a class="headerlink" href="#functions" title="Link to this heading"></a></h2> <span id="id3"></span><h2><span class="section-number">4.2. </span>Functions<a class="headerlink" href="#functions" title="Permalink to this heading"></a></h2> <p>If <code class="docutils literal notranslate"><span class="pre">f</span> <span class="pre">:</span> <span class="pre">α</span> <span class="pre">→</span> <span class="pre">β</span></code> is a function and <code class="docutils literal notranslate"><span class="pre">p</span></code> is a set of elements of type <code class="docutils literal notranslate"><span class="pre">β</span></code>, the library defines <code class="docutils literal notranslate"><span class="pre">preimage</span> <span class="pre">f</span> <span class="pre">p</span></code>, written <code class="docutils literal notranslate"><span class="pre">f</span> <span class="pre">⁻¹'</span> <span class="pre">p</span></code>, to be <code class="docutils literal notranslate"><span class="pre">{x</span> <span class="pre">|</span> <span class="pre">f</span> <span class="pre">x</span> <span class="pre">∈</span> <span class="pre">p}</span></code>. The expression <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">∈</span> <span class="pre">f</span> <span class="pre">⁻¹'</span> <span class="pre">p</span></code> reduces to <code class="docutils literal notranslate"><span class="pre">f</span> <span class="pre">x</span> <span class="pre">∈</span> <span class="pre">p</span></code>. This is often convenient, as in the following example:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="n">β</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">β</span><span class="o">)</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">α</span><span class="o">)</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">u</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">β</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">α</span> <span class="n">β</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">β</span><span class="o">)</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">s</span> <span class="n">t</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">α</span><span class="o">)</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">u</span> <span class="n">v</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">β</span><span class="o">)</span> <span class="kn">open</span><span class="w"> </span><span class="n">Function</span> <span class="kn">open</span><span class="w"> </span><span class="n">Set</span> <span class="kn">open</span> <span class="n">Function</span> <span class="kn">open</span> <span class="n">Set</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">⁻¹'</span><span class="w"> </span><span class="o">(</span><span class="n">u</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">v</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">⁻¹'</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">⁻¹'</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">ext</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">f</span> <span class="bp">⁻¹'</span> <span class="o">(</span><span class="n">u</span> <span class="bp">∩</span> <span class="n">v</span><span class="o">)</span> <span class="bp">=</span> <span class="n">f</span> <span class="bp">⁻¹'</span> <span class="n">u</span> <span class="bp">∩</span> <span class="n">f</span> <span class="bp">⁻¹'</span> <span class="n">v</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">ext</span> <span class="n">rfl</span> </pre></div> </div> <p>If <code class="docutils literal notranslate"><span class="pre">s</span></code> is a set of elements of type <code class="docutils literal notranslate"><span class="pre">α</span></code>,
-
@@ -587,25 +583,25 @@ So a hypothesis <code class="docutils literal notranslate"><span class="pre">y<and <code class="docutils literal notranslate"><span class="pre">xeq</span> <span class="pre">:</span> <span class="pre">f</span> <span class="pre">x</span> <span class="pre">=</span> <span class="pre">y</span></code>. The <code class="docutils literal notranslate"><span class="pre">rfl</span></code> tag in the <code class="docutils literal notranslate"><span class="pre">rintro</span></code> tactic (see <a class="reference internal" href="C03_Logic.html#the-existential-quantifier"><span class="std std-numref">Section 3.2</span></a>) was made precisely for this sort of situation.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">t</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">ext</span><span class="w"> </span><span class="n">y</span><span class="bp">;</span><span class="w"> </span><span class="n">constructor</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">rintro</span><span class="w"> </span><span class="o">⟨</span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">xs</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">xt</span><span class="o">,</span><span class="w"> </span><span class="n">rfl</span><span class="o">⟩</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">left</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">xs</span> <span class="w"> </span><span class="n">right</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">xt</span> <span class="w"> </span><span class="n">rintro</span><span class="w"> </span><span class="o">(⟨</span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">xs</span><span class="o">,</span><span class="w"> </span><span class="n">rfl</span><span class="o">⟩</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="o">⟨</span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">xt</span><span class="o">,</span><span class="w"> </span><span class="n">rfl</span><span class="o">⟩)</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">Or.inl</span><span class="w"> </span><span class="n">xs</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">Or.inr</span><span class="w"> </span><span class="n">xt</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">f</span> <span class="bp">''</span> <span class="o">(</span><span class="n">s</span> <span class="bp">∪</span> <span class="n">t</span><span class="o">)</span> <span class="bp">=</span> <span class="n">f</span> <span class="bp">''</span> <span class="n">s</span> <span class="bp">∪</span> <span class="n">f</span> <span class="bp">''</span> <span class="n">t</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">ext</span> <span class="n">y</span><span class="bp">;</span> <span class="n">constructor</span> <span class="bp">·</span> <span class="n">rintro</span> <span class="o">⟨</span><span class="n">x</span><span class="o">,</span> <span class="n">xs</span> <span class="bp">|</span> <span class="n">xt</span><span class="o">,</span> <span class="n">rfl</span><span class="o">⟩</span> <span class="bp">·</span> <span class="n">left</span> <span class="n">use</span> <span class="n">x</span><span class="o">,</span> <span class="n">xs</span> <span class="n">right</span> <span class="n">use</span> <span class="n">x</span><span class="o">,</span> <span class="n">xt</span> <span class="n">rintro</span> <span class="o">(⟨</span><span class="n">x</span><span class="o">,</span> <span class="n">xs</span><span class="o">,</span> <span class="n">rfl</span><span class="o">⟩</span> <span class="bp">|</span> <span class="o">⟨</span><span class="n">x</span><span class="o">,</span> <span class="n">xt</span><span class="o">,</span> <span class="n">rfl</span><span class="o">⟩)</span> <span class="bp">·</span> <span class="n">use</span> <span class="n">x</span><span class="o">,</span> <span class="n">Or.inl</span> <span class="n">xs</span> <span class="n">use</span> <span class="n">x</span><span class="o">,</span> <span class="n">Or.inr</span> <span class="n">xt</span> </pre></div> </div> <p>Notice also that the <code class="docutils literal notranslate"><span class="pre">use</span></code> tactic applies <code class="docutils literal notranslate"><span class="pre">rfl</span></code> to close goals when it can.</p> <p>Here is another example:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">⁻¹'</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="n">s</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">xs</span> <span class="w"> </span><span class="k">show</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="n">s</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">xs</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">s</span> <span class="bp">⊆</span> <span class="n">f</span> <span class="bp">⁻¹'</span> <span class="o">(</span><span class="n">f</span> <span class="bp">''</span> <span class="n">s</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">x</span> <span class="n">xs</span> <span class="k">show</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">f</span> <span class="bp">''</span> <span class="n">s</span> <span class="n">use</span> <span class="n">x</span><span class="o">,</span> <span class="n">xs</span> </pre></div> </div> <p>We can replace the line <code class="docutils literal notranslate"><span class="pre">use</span> <span class="pre">x,</span> <span class="pre">xs</span></code> by
-
@@ -614,8 +610,8 @@ use a theorem specifically designed for that purpose.But knowing that the image is defined in terms of an existential quantifier is often convenient.</p> <p>The following equivalence is a good exercise:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">⁻¹'</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">f</span> <span class="bp">''</span> <span class="n">s</span> <span class="bp">⊆</span> <span class="n">v</span> <span class="bp">↔</span> <span class="n">s</span> <span class="bp">⊆</span> <span class="n">f</span> <span class="bp">⁻¹'</span> <span class="n">v</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>It shows that <code class="docutils literal notranslate"><span class="pre">image</span> <span class="pre">f</span></code> and <code class="docutils literal notranslate"><span class="pre">preimage</span> <span class="pre">f</span></code> are
-
@@ -634,47 +630,47 @@ you to enjoy.You don’t have to do all of them at once; do a few of them, and set the rest aside for a rainy day.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Injective</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">⁻¹'</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="n">s</span><span class="o">)</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">Injective</span> <span class="n">f</span><span class="o">)</span> <span class="o">:</span> <span class="n">f</span> <span class="bp">⁻¹'</span> <span class="o">(</span><span class="n">f</span> <span class="bp">''</span> <span class="n">s</span><span class="o">)</span> <span class="bp">⊆</span> <span class="n">s</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="bp">⁻¹'</span><span class="w"> </span><span class="n">u</span><span class="o">)</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">f</span> <span class="bp">''</span> <span class="o">(</span><span class="n">f</span> <span class="bp">⁻¹'</span> <span class="n">u</span><span class="o">)</span> <span class="bp">⊆</span> <span class="n">u</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Surjective</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="bp">⁻¹'</span><span class="w"> </span><span class="n">u</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">Surjective</span> <span class="n">f</span><span class="o">)</span> <span class="o">:</span> <span class="n">u</span> <span class="bp">⊆</span> <span class="n">f</span> <span class="bp">''</span> <span class="o">(</span><span class="n">f</span> <span class="bp">⁻¹'</span> <span class="n">u</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">t</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">s</span> <span class="bp">⊆</span> <span class="n">t</span><span class="o">)</span> <span class="o">:</span> <span class="n">f</span> <span class="bp">''</span> <span class="n">s</span> <span class="bp">⊆</span> <span class="n">f</span> <span class="bp">''</span> <span class="n">t</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">v</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">⁻¹'</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">⁻¹'</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">u</span> <span class="bp">⊆</span> <span class="n">v</span><span class="o">)</span> <span class="o">:</span> <span class="n">f</span> <span class="bp">⁻¹'</span> <span class="n">u</span> <span class="bp">⊆</span> <span class="n">f</span> <span class="bp">⁻¹'</span> <span class="n">v</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">⁻¹'</span><span class="w"> </span><span class="o">(</span><span class="n">u</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">v</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">⁻¹'</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">⁻¹'</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">f</span> <span class="bp">⁻¹'</span> <span class="o">(</span><span class="n">u</span> <span class="bp">∪</span> <span class="n">v</span><span class="o">)</span> <span class="bp">=</span> <span class="n">f</span> <span class="bp">⁻¹'</span> <span class="n">u</span> <span class="bp">∪</span> <span class="n">f</span> <span class="bp">⁻¹'</span> <span class="n">v</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">t</span><span class="o">)</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">f</span> <span class="bp">''</span> <span class="o">(</span><span class="n">s</span> <span class="bp">∩</span> <span class="n">t</span><span class="o">)</span> <span class="bp">⊆</span> <span class="n">f</span> <span class="bp">''</span> <span class="n">s</span> <span class="bp">∩</span> <span class="n">f</span> <span class="bp">''</span> <span class="n">t</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Injective</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">t</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">Injective</span> <span class="n">f</span><span class="o">)</span> <span class="o">:</span> <span class="n">f</span> <span class="bp">''</span> <span class="n">s</span> <span class="bp">∩</span> <span class="n">f</span> <span class="bp">''</span> <span class="n">t</span> <span class="bp">⊆</span> <span class="n">f</span> <span class="bp">''</span> <span class="o">(</span><span class="n">s</span> <span class="bp">∩</span> <span class="n">t</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">\</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="bp">\</span><span class="w"> </span><span class="n">t</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">f</span> <span class="bp">''</span> <span class="n">s</span> <span class="bp">\</span> <span class="n">f</span> <span class="bp">''</span> <span class="n">t</span> <span class="bp">⊆</span> <span class="n">f</span> <span class="bp">''</span> <span class="o">(</span><span class="n">s</span> <span class="bp">\</span> <span class="n">t</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">⁻¹'</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="bp">\</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">⁻¹'</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">⁻¹'</span><span class="w"> </span><span class="o">(</span><span class="n">u</span><span class="w"> </span><span class="bp">\</span><span class="w"> </span><span class="n">v</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">f</span> <span class="bp">⁻¹'</span> <span class="n">u</span> <span class="bp">\</span> <span class="n">f</span> <span class="bp">⁻¹'</span> <span class="n">v</span> <span class="bp">⊆</span> <span class="n">f</span> <span class="bp">⁻¹'</span> <span class="o">(</span><span class="n">u</span> <span class="bp">\</span> <span class="n">v</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">⁻¹'</span><span class="w"> </span><span class="n">v</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">f</span> <span class="bp">''</span> <span class="n">s</span> <span class="bp">∩</span> <span class="n">v</span> <span class="bp">=</span> <span class="n">f</span> <span class="bp">''</span> <span class="o">(</span><span class="n">s</span> <span class="bp">∩</span> <span class="n">f</span> <span class="bp">⁻¹'</span> <span class="n">v</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">⁻¹'</span><span class="w"> </span><span class="n">u</span><span class="o">)</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">f</span> <span class="bp">''</span> <span class="o">(</span><span class="n">s</span> <span class="bp">∩</span> <span class="n">f</span> <span class="bp">⁻¹'</span> <span class="n">u</span><span class="o">)</span> <span class="bp">⊆</span> <span class="n">f</span> <span class="bp">''</span> <span class="n">s</span> <span class="bp">∩</span> <span class="n">u</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">⁻¹'</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">⁻¹'</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">u</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">s</span> <span class="bp">∩</span> <span class="n">f</span> <span class="bp">⁻¹'</span> <span class="n">u</span> <span class="bp">⊆</span> <span class="n">f</span> <span class="bp">⁻¹'</span> <span class="o">(</span><span class="n">f</span> <span class="bp">''</span> <span class="n">s</span> <span class="bp">∩</span> <span class="n">u</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">⁻¹'</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">⁻¹'</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">u</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">s</span> <span class="bp">∪</span> <span class="n">f</span> <span class="bp">⁻¹'</span> <span class="n">u</span> <span class="bp">⊆</span> <span class="n">f</span> <span class="bp">⁻¹'</span> <span class="o">(</span><span class="n">f</span> <span class="bp">''</span> <span class="n">s</span> <span class="bp">∪</span> <span class="n">u</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>You can also try your hand at the next group of exercises,
-
@@ -685,29 +681,29 @@ to guarantee that the index set is nonempty.To prove any of these, we recommend using <code class="docutils literal notranslate"><span class="pre">ext</span></code> or <code class="docutils literal notranslate"><span class="pre">intro</span></code> to unfold the meaning of an equation or inclusion between sets, and then calling <code class="docutils literal notranslate"><span class="pre">simp</span></code> to unpack the conditions for membership.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">I</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">A</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">α</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">B</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">β</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">I</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">(</span><span class="n">A</span> <span class="o">:</span> <span class="n">I</span> <span class="bp">→</span> <span class="n">Set</span> <span class="n">α</span><span class="o">)</span> <span class="o">(</span><span class="n">B</span> <span class="o">:</span> <span class="n">I</span> <span class="bp">→</span> <span class="n">Set</span> <span class="n">β</span><span class="o">)</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="bp">⋃</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">⋃</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">:</span> <span class="o">(</span><span class="n">f</span> <span class="bp">''</span> <span class="bp">⋃</span> <span class="n">i</span><span class="o">,</span> <span class="n">A</span> <span class="n">i</span><span class="o">)</span> <span class="bp">=</span> <span class="bp">⋃</span> <span class="n">i</span><span class="o">,</span> <span class="n">f</span> <span class="bp">''</span> <span class="n">A</span> <span class="n">i</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="bp">⋂</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="bp">⋂</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">:</span> <span class="o">(</span><span class="n">f</span> <span class="bp">''</span> <span class="bp">⋂</span> <span class="n">i</span><span class="o">,</span> <span class="n">A</span> <span class="n">i</span><span class="o">)</span> <span class="bp">⊆</span> <span class="bp">⋂</span> <span class="n">i</span><span class="o">,</span> <span class="n">f</span> <span class="bp">''</span> <span class="n">A</span> <span class="n">i</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">i</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">I</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">injf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Injective</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="bp">⋂</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="bp">⋂</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">i</span> <span class="o">:</span> <span class="n">I</span><span class="o">)</span> <span class="o">(</span><span class="n">injf</span> <span class="o">:</span> <span class="n">Injective</span> <span class="n">f</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="bp">⋂</span> <span class="n">i</span><span class="o">,</span> <span class="n">f</span> <span class="bp">''</span> <span class="n">A</span> <span class="n">i</span><span class="o">)</span> <span class="bp">⊆</span> <span class="n">f</span> <span class="bp">''</span> <span class="bp">⋂</span> <span class="n">i</span><span class="o">,</span> <span class="n">A</span> <span class="n">i</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="bp">⁻¹'</span><span class="w"> </span><span class="bp">⋃</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">⋃</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">⁻¹'</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">:</span> <span class="o">(</span><span class="n">f</span> <span class="bp">⁻¹'</span> <span class="bp">⋃</span> <span class="n">i</span><span class="o">,</span> <span class="n">B</span> <span class="n">i</span><span class="o">)</span> <span class="bp">=</span> <span class="bp">⋃</span> <span class="n">i</span><span class="o">,</span> <span class="n">f</span> <span class="bp">⁻¹'</span> <span class="n">B</span> <span class="n">i</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="bp">⁻¹'</span><span class="w"> </span><span class="bp">⋂</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">⋂</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">⁻¹'</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">:</span> <span class="o">(</span><span class="n">f</span> <span class="bp">⁻¹'</span> <span class="bp">⋂</span> <span class="n">i</span><span class="o">,</span> <span class="n">B</span> <span class="n">i</span><span class="o">)</span> <span class="bp">=</span> <span class="bp">⋂</span> <span class="n">i</span><span class="o">,</span> <span class="n">f</span> <span class="bp">⁻¹'</span> <span class="n">B</span> <span class="n">i</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>The library defines a predicate <code class="docutils literal notranslate"><span class="pre">InjOn</span> <span class="pre">f</span> <span class="pre">s</span></code> to say that <code class="docutils literal notranslate"><span class="pre">f</span></code> is injective on <code class="docutils literal notranslate"><span class="pre">s</span></code>. It is defined as follows:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">InjOn</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x₁</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x₂</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x₁</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x₂</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">x₁</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x₂</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Iff.refl</span><span class="w"> </span><span class="n">_</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">InjOn</span> <span class="n">f</span> <span class="n">s</span> <span class="bp">↔</span> <span class="bp">∀</span> <span class="n">x₁</span> <span class="bp">∈</span> <span class="n">s</span><span class="o">,</span> <span class="bp">∀</span> <span class="n">x₂</span> <span class="bp">∈</span> <span class="n">s</span><span class="o">,</span> <span class="n">f</span> <span class="n">x₁</span> <span class="bp">=</span> <span class="n">f</span> <span class="n">x₂</span> <span class="bp">→</span> <span class="n">x₁</span> <span class="bp">=</span> <span class="n">x₂</span> <span class="o">:=</span> <span class="n">Iff.refl</span> <span class="n">_</span> </pre></div> </div> <p>The statement <code class="docutils literal notranslate"><span class="pre">Injective</span> <span class="pre">f</span></code> is provably equivalent
-
@@ -721,39 +717,39 @@ to their full domain,there are often relativized versions that restrict the statements to a subset of the domain type.</p> <p>Here is are some examples of <code class="docutils literal notranslate"><span class="pre">InjOn</span></code> and <code class="docutils literal notranslate"><span class="pre">range</span></code> in use:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">Real</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">InjOn</span><span class="w"> </span><span class="n">log</span><span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">}</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">xpos</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">ypos</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">e</span> <span class="w"> </span><span class="c1">-- log x = log y</span> <span class="w"> </span><span class="k">calc</span> <span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">exp</span><span class="w"> </span><span class="o">(</span><span class="n">log</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">exp_log</span><span class="w"> </span><span class="n">xpos</span><span class="o">]</span> <span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">exp</span><span class="w"> </span><span class="o">(</span><span class="n">log</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">e</span><span class="o">]</span> <span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">exp_log</span><span class="w"> </span><span class="n">ypos</span><span class="o">]</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">range</span><span class="w"> </span><span class="n">exp</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">}</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">ext</span><span class="w"> </span><span class="n">y</span><span class="bp">;</span><span class="w"> </span><span class="n">constructor</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">rintro</span><span class="w"> </span><span class="o">⟨</span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">rfl</span><span class="o">⟩</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">exp_pos</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">ypos</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">log</span><span class="w"> </span><span class="n">y</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">exp_log</span><span class="w"> </span><span class="n">ypos</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span> <span class="n">Set</span> <span class="n">Real</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">InjOn</span> <span class="n">log</span> <span class="o">{</span> <span class="n">x</span> <span class="bp">|</span> <span class="n">x</span> <span class="bp">></span> <span class="mi">0</span> <span class="o">}</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">x</span> <span class="n">xpos</span> <span class="n">y</span> <span class="n">ypos</span> <span class="n">intro</span> <span class="n">e</span> <span class="c1">-- log x = log y</span> <span class="k">calc</span> <span class="n">x</span> <span class="bp">=</span> <span class="n">exp</span> <span class="o">(</span><span class="n">log</span> <span class="n">x</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">exp_log</span> <span class="n">xpos</span><span class="o">]</span> <span class="n">_</span> <span class="bp">=</span> <span class="n">exp</span> <span class="o">(</span><span class="n">log</span> <span class="n">y</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">e</span><span class="o">]</span> <span class="n">_</span> <span class="bp">=</span> <span class="n">y</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">exp_log</span> <span class="n">ypos</span><span class="o">]</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">range</span> <span class="n">exp</span> <span class="bp">=</span> <span class="o">{</span> <span class="n">y</span> <span class="bp">|</span> <span class="n">y</span> <span class="bp">></span> <span class="mi">0</span> <span class="o">}</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">ext</span> <span class="n">y</span><span class="bp">;</span> <span class="n">constructor</span> <span class="bp">·</span> <span class="n">rintro</span> <span class="o">⟨</span><span class="n">x</span><span class="o">,</span> <span class="n">rfl</span><span class="o">⟩</span> <span class="n">apply</span> <span class="n">exp_pos</span> <span class="n">intro</span> <span class="n">ypos</span> <span class="n">use</span> <span class="n">log</span> <span class="n">y</span> <span class="n">rw</span> <span class="o">[</span><span class="n">exp_log</span> <span class="n">ypos</span><span class="o">]</span> </pre></div> </div> <p>Try proving these:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">InjOn</span><span class="w"> </span><span class="n">sqrt</span><span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≥</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">}</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">InjOn</span> <span class="n">sqrt</span> <span class="o">{</span> <span class="n">x</span> <span class="bp">|</span> <span class="n">x</span> <span class="bp">≥</span> <span class="mi">0</span> <span class="o">}</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">InjOn</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≥</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">}</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">InjOn</span> <span class="o">(</span><span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">x</span> <span class="bp">^</span> <span class="mi">2</span><span class="o">)</span> <span class="o">{</span> <span class="n">x</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">|</span> <span class="n">x</span> <span class="bp">≥</span> <span class="mi">0</span> <span class="o">}</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">sqrt</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≥</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">}</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">≥</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">}</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">sqrt</span> <span class="bp">''</span> <span class="o">{</span> <span class="n">x</span> <span class="bp">|</span> <span class="n">x</span> <span class="bp">≥</span> <span class="mi">0</span> <span class="o">}</span> <span class="bp">=</span> <span class="o">{</span> <span class="n">y</span> <span class="bp">|</span> <span class="n">y</span> <span class="bp">≥</span> <span class="mi">0</span> <span class="o">}</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">range</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">≥</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">}</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">:</span> <span class="o">(</span><span class="n">range</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">x</span> <span class="bp">^</span> <span class="mi">2</span><span class="o">)</span> <span class="bp">=</span> <span class="o">{</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">|</span> <span class="n">y</span> <span class="bp">≥</span> <span class="mi">0</span> <span class="o">}</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>To define the inverse of a function <code class="docutils literal notranslate"><span class="pre">f</span> <span class="pre">:</span> <span class="pre">α</span> <span class="pre">→</span> <span class="pre">β</span></code>,
-
@@ -773,16 +769,16 @@ This requires an appeal to the <em>axiom of choice</em>.Lean allows various ways of accessing it; one convenient method is to use the classical <code class="docutils literal notranslate"><span class="pre">choose</span></code> operator, illustrated below.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="n">β</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Inhabited</span><span class="w"> </span><span class="n">α</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">α</span> <span class="n">β</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Inhabited</span> <span class="n">α</span><span class="o">]</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">default</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">default</span> <span class="o">:</span> <span class="n">α</span><span class="o">)</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">P</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="kt">Prop</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="n">x</span><span class="o">)</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">P</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="kt">Prop</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">x</span><span class="o">,</span> <span class="n">P</span> <span class="n">x</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="n">Classical.choose</span><span class="w"> </span><span class="n">h</span> <span class="k">#check</span> <span class="n">Classical.choose</span> <span class="n">h</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="o">(</span><span class="n">Classical.choose</span><span class="w"> </span><span class="n">h</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Classical.choose_spec</span><span class="w"> </span><span class="n">h</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">P</span> <span class="o">(</span><span class="n">Classical.choose</span> <span class="n">h</span><span class="o">)</span> <span class="o">:=</span> <span class="n">Classical.choose_spec</span> <span class="n">h</span> </pre></div> </div> <p>Given <code class="docutils literal notranslate"><span class="pre">h</span> <span class="pre">:</span> <span class="pre">∃</span> <span class="pre">x,</span> <span class="pre">P</span> <span class="pre">x</span></code>, the value of <code class="docutils literal notranslate"><span class="pre">Classical.choose</span> <span class="pre">h</span></code>
-
@@ -791,16 +787,16 @@ The theorem <code class="docutils literal notranslate"><span class="pre">Classicmeets this specification.</p> <p>With these in hand, we can define the inverse function as follows:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">noncomputable</span><span class="w"> </span><span class="kn">section</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">noncomputable</span> <span class="kn">section</span> <span class="kn">open</span><span class="w"> </span><span class="n">Classical</span> <span class="kn">open</span> <span class="n">Classical</span> <span class="kd">def</span><span class="w"> </span><span class="n">inverse</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">β</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">β</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">β</span><span class="w"> </span><span class="bp">↦</span> <span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="k">then</span><span class="w"> </span><span class="n">Classical.choose</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="n">default</span> <span class="kd">def</span> <span class="n">inverse</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">β</span><span class="o">)</span> <span class="o">:</span> <span class="n">β</span> <span class="bp">→</span> <span class="n">α</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">y</span> <span class="o">:</span> <span class="n">β</span> <span class="bp">↦</span> <span class="k">if</span> <span class="n">h</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">x</span><span class="o">,</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">=</span> <span class="n">y</span> <span class="k">then</span> <span class="n">Classical.choose</span> <span class="n">h</span> <span class="k">else</span> <span class="n">default</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">inverse_spec</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">β</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">β</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">inverse</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">inverse</span><span class="o">,</span><span class="w"> </span><span class="n">dif_pos</span><span class="w"> </span><span class="n">h</span><span class="o">]</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">Classical.choose_spec</span><span class="w"> </span><span class="n">h</span> <span class="kd">theorem</span> <span class="n">inverse_spec</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">β</span><span class="o">}</span> <span class="o">(</span><span class="n">y</span> <span class="o">:</span> <span class="n">β</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">x</span><span class="o">,</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">=</span> <span class="n">y</span><span class="o">)</span> <span class="o">:</span> <span class="n">f</span> <span class="o">(</span><span class="n">inverse</span> <span class="n">f</span> <span class="n">y</span><span class="o">)</span> <span class="bp">=</span> <span class="n">y</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">inverse</span><span class="o">,</span> <span class="n">dif_pos</span> <span class="n">h</span><span class="o">]</span> <span class="n">exact</span> <span class="n">Classical.choose_spec</span> <span class="n">h</span> </pre></div> </div> <p>The lines <code class="docutils literal notranslate"><span class="pre">noncomputable</span> <span class="pre">section</span></code> and <code class="docutils literal notranslate"><span class="pre">open</span> <span class="pre">Classical</span></code>
-
@@ -833,15 +829,15 @@ You should be able to prove each of them with about a half-dozenshort lines. If you are looking for an extra challenge, try to condense each proof to a single-line proof term.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">β</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">β</span><span class="o">)</span> <span class="kn">open</span><span class="w"> </span><span class="n">Function</span> <span class="kn">open</span> <span class="n">Function</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Injective</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">LeftInverse</span><span class="w"> </span><span class="o">(</span><span class="n">inverse</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">Injective</span> <span class="n">f</span> <span class="bp">↔</span> <span class="n">LeftInverse</span> <span class="o">(</span><span class="n">inverse</span> <span class="n">f</span><span class="o">)</span> <span class="n">f</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Surjective</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">RightInverse</span><span class="w"> </span><span class="o">(</span><span class="n">inverse</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">Surjective</span> <span class="n">f</span> <span class="bp">↔</span> <span class="n">RightInverse</span> <span class="o">(</span><span class="n">inverse</span> <span class="n">f</span><span class="o">)</span> <span class="n">f</span> <span class="o">:=</span> <span class="gr">sorry</span> </pre></div> </div> <p>We close this section with a type-theoretic statement of Cantor’s
-
@@ -849,24 +845,24 @@ famous theorem that there is no surjective function from a setto its power set. See if you can understand the proof, and then fill in the two lines that are missing.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">Cantor</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">α</span><span class="o">,</span><span class="w"> </span><span class="bp">¬</span><span class="n">Surjective</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">surjf</span> <span class="w"> </span><span class="k">let</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp">∉</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">}</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">surjf</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">j</span><span class="o">,</span><span class="w"> </span><span class="n">h</span><span class="o">⟩</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">h₁</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">j</span><span class="w"> </span><span class="bp">∉</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">j</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">h'</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">j</span><span class="w"> </span><span class="bp">∉</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">j</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">rwa</span><span class="w"> </span><span class="o">[</span><span class="n">h</span><span class="o">]</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">h'</span> <span class="w"> </span><span class="n">contradiction</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">h₂</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">j</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">S</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">h₃</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">j</span><span class="w"> </span><span class="bp">∉</span><span class="w"> </span><span class="n">S</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">contradiction</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">Cantor</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">f</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">Set</span> <span class="n">α</span><span class="o">,</span> <span class="bp">¬</span><span class="n">Surjective</span> <span class="n">f</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">f</span> <span class="n">surjf</span> <span class="k">let</span> <span class="n">S</span> <span class="o">:=</span> <span class="o">{</span> <span class="n">i</span> <span class="bp">|</span> <span class="n">i</span> <span class="bp">∉</span> <span class="n">f</span> <span class="n">i</span> <span class="o">}</span> <span class="n">rcases</span> <span class="n">surjf</span> <span class="n">S</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">j</span><span class="o">,</span> <span class="n">h</span><span class="o">⟩</span> <span class="k">have</span> <span class="n">h₁</span> <span class="o">:</span> <span class="n">j</span> <span class="bp">∉</span> <span class="n">f</span> <span class="n">j</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">h'</span> <span class="k">have</span> <span class="o">:</span> <span class="n">j</span> <span class="bp">∉</span> <span class="n">f</span> <span class="n">j</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rwa</span> <span class="o">[</span><span class="n">h</span><span class="o">]</span> <span class="n">at</span> <span class="n">h'</span> <span class="n">contradiction</span> <span class="k">have</span> <span class="n">h₂</span> <span class="o">:</span> <span class="n">j</span> <span class="bp">∈</span> <span class="n">S</span> <span class="gr">sorry</span> <span class="k">have</span> <span class="n">h₃</span> <span class="o">:</span> <span class="n">j</span> <span class="bp">∉</span> <span class="n">S</span> <span class="gr">sorry</span> <span class="n">contradiction</span> </pre></div> </div> </section> <section id="the-schroder-bernstein-theorem"> <span id="the-schroeder-bernstein-theorem"></span><h2><span class="section-number">4.3. </span>The Schröder-Bernstein Theorem<a class="headerlink" href="#the-schroder-bernstein-theorem" title="Link to this heading"></a></h2> <span id="the-schroeder-bernstein-theorem"></span><h2><span class="section-number">4.3. </span>The Schröder-Bernstein Theorem<a class="headerlink" href="#the-schroder-bernstein-theorem" title="Permalink to this heading"></a></h2> <p>We close this chapter with an elementary but nontrivial theorem of set theory. Let <span class="math notranslate nohighlight">\(\alpha\)</span> and <span class="math notranslate nohighlight">\(\beta\)</span> be sets. (In our formalization, they will actually be types.)
-
@@ -889,22 +885,19 @@ to the formal proof of a real mathematical result.</p><span class="math notranslate nohighlight">\(g\)</span> in <span class="math notranslate nohighlight">\(\alpha\)</span>. On that image, the inverse of <span class="math notranslate nohighlight">\(g\)</span> is defined and is a bijection with <span class="math notranslate nohighlight">\(\beta\)</span>.</p> <a class="reference internal image-reference" href="_images/schroeder_bernstein1.png"><img alt="the Schröder Bernstein theorem" class="align-center" src="_images/schroeder_bernstein1.png" style="height: 150px;" /> </a> <a class="reference internal image-reference" href="_images/schroeder_bernstein1.png"><img alt="the Schröder Bernstein theorem" class="align-center" src="_images/schroeder_bernstein1.png" style="height: 150px;" /></a> <p>The problem is that the bijection does not include the shaded region in the diagram, which is nonempty if <span class="math notranslate nohighlight">\(g\)</span> is not surjective. Alternatively, we can use <span class="math notranslate nohighlight">\(f\)</span> to map all of <span class="math notranslate nohighlight">\(\alpha\)</span> to <span class="math notranslate nohighlight">\(\beta\)</span>, but in that case the problem is that if <span class="math notranslate nohighlight">\(f\)</span> is not surjective, it will miss some elements of <span class="math notranslate nohighlight">\(\beta\)</span>.</p> <a class="reference internal image-reference" href="_images/schroeder_bernstein2.png"><img alt="the Schröder Bernstein theorem" class="align-center" src="_images/schroeder_bernstein2.png" style="height: 150px;" /> </a> <a class="reference internal image-reference" href="_images/schroeder_bernstein2.png"><img alt="the Schröder Bernstein theorem" class="align-center" src="_images/schroeder_bernstein2.png" style="height: 150px;" /></a> <p>But now consider the composition <span class="math notranslate nohighlight">\(g \circ f\)</span> from <span class="math notranslate nohighlight">\(\alpha\)</span> to itself. Because the composition is injective, it forms a bijection between <span class="math notranslate nohighlight">\(\alpha\)</span> and its image, yielding a scaled-down copy of <span class="math notranslate nohighlight">\(\alpha\)</span> inside itself.</p> <a class="reference internal image-reference" href="_images/schroeder_bernstein3.png"><img alt="the Schröder Bernstein theorem" class="align-center" src="_images/schroeder_bernstein3.png" style="height: 150px;" /> </a> <a class="reference internal image-reference" href="_images/schroeder_bernstein3.png"><img alt="the Schröder Bernstein theorem" class="align-center" src="_images/schroeder_bernstein3.png" style="height: 150px;" /></a> <p>This composition maps the inner shaded ring to yet another such set, which we can think of as an even smaller concentric shaded ring, and so on.
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@@ -944,9 +937,9 @@ Formalizing the proof will not only improve our confidence in theresult, but also help us understand it better. Because the proof uses classical logic, we tell Lean that our definitions will generally not be computable.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">noncomputable</span><span class="w"> </span><span class="kn">section</span> <span class="kn">open</span><span class="w"> </span><span class="n">Classical</span> <span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="n">β</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Nonempty</span><span class="w"> </span><span class="n">β</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">noncomputable</span> <span class="kn">section</span> <span class="kn">open</span> <span class="n">Classical</span> <span class="kd">variable</span> <span class="o">{</span><span class="n">α</span> <span class="n">β</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Nonempty</span> <span class="n">β</span><span class="o">]</span> </pre></div> </div> <p>The annotation <code class="docutils literal notranslate"><span class="pre">[Nonempty</span> <span class="pre">β]</span></code> specifies that <code class="docutils literal notranslate"><span class="pre">β</span></code> is nonempty.
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@@ -962,21 +955,21 @@ in <code class="docutils literal notranslate"><span class="pre">β</span></cand returns an arbitrary element of <code class="docutils literal notranslate"><span class="pre">β</span></code> otherwise. The function <code class="docutils literal notranslate"><span class="pre">invFun</span> <span class="pre">g</span></code> is always a left inverse if <code class="docutils literal notranslate"><span class="pre">g</span></code> is injective and a right inverse if <code class="docutils literal notranslate"><span class="pre">g</span></code> is surjective.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">invFun</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">β</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">leftInverse_invFun</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Injective</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">LeftInverse</span><span class="w"> </span><span class="o">(</span><span class="n">invFun</span><span class="w"> </span><span class="n">g</span><span class="o">)</span><span class="w"> </span><span class="n">g</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">leftInverse_invFun</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Injective</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">y</span><span class="o">,</span><span class="w"> </span><span class="n">invFun</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="o">(</span><span class="n">g</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">y</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">invFun_eq</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="bp">∃</span><span class="w"> </span><span class="n">y</span><span class="o">,</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="o">(</span><span class="n">invFun</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="o">(</span><span class="n">invFun</span> <span class="n">g</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">β</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">leftInverse_invFun</span> <span class="o">:</span> <span class="n">Injective</span> <span class="n">g</span> <span class="bp">→</span> <span class="n">LeftInverse</span> <span class="o">(</span><span class="n">invFun</span> <span class="n">g</span><span class="o">)</span> <span class="n">g</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">leftInverse_invFun</span> <span class="o">:</span> <span class="n">Injective</span> <span class="n">g</span> <span class="bp">→</span> <span class="bp">∀</span> <span class="n">y</span><span class="o">,</span> <span class="n">invFun</span> <span class="n">g</span> <span class="o">(</span><span class="n">g</span> <span class="n">y</span><span class="o">)</span> <span class="bp">=</span> <span class="n">y</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">invFun_eq</span> <span class="o">:</span> <span class="o">(</span><span class="bp">∃</span> <span class="n">y</span><span class="o">,</span> <span class="n">g</span> <span class="n">y</span> <span class="bp">=</span> <span class="n">x</span><span class="o">)</span> <span class="bp">→</span> <span class="n">g</span> <span class="o">(</span><span class="n">invFun</span> <span class="n">g</span> <span class="n">x</span><span class="o">)</span> <span class="bp">=</span> <span class="n">x</span><span class="o">)</span> </pre></div> </div> <p>We define the set corresponding to the union of the shaded regions as follows.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">β</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">g</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">β</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">α</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">β</span><span class="o">)</span> <span class="o">(</span><span class="n">g</span> <span class="o">:</span> <span class="n">β</span> <span class="bp">→</span> <span class="n">α</span><span class="o">)</span> <span class="kd">def</span><span class="w"> </span><span class="n">sbAux</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">α</span> <span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">=></span><span class="w"> </span><span class="n">univ</span><span class="w"> </span><span class="bp">\</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="n">univ</span> <span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">=></span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="n">sbAux</span><span class="w"> </span><span class="n">n</span><span class="o">)</span> <span class="kd">def</span> <span class="n">sbAux</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">Set</span> <span class="n">α</span> <span class="bp">|</span> <span class="mi">0</span> <span class="bp">=></span> <span class="n">univ</span> <span class="bp">\</span> <span class="n">g</span> <span class="bp">''</span> <span class="n">univ</span> <span class="bp">|</span> <span class="n">n</span> <span class="bp">+</span> <span class="mi">1</span> <span class="bp">=></span> <span class="n">g</span> <span class="bp">''</span> <span class="o">(</span><span class="n">f</span> <span class="bp">''</span> <span class="n">sbAux</span> <span class="n">n</span><span class="o">)</span> <span class="kd">def</span><span class="w"> </span><span class="n">sbSet</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="bp">⋃</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="n">sbAux</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">n</span> <span class="kd">def</span> <span class="n">sbSet</span> <span class="o">:=</span> <span class="bp">⋃</span> <span class="n">n</span><span class="o">,</span> <span class="n">sbAux</span> <span class="n">f</span> <span class="n">g</span> <span class="n">n</span> </pre></div> </div> <p>The definition <code class="docutils literal notranslate"><span class="pre">sbAux</span></code> is an example of a <em>recursive definition</em>,
-
@@ -988,8 +981,8 @@ S_{n+1} &= g(f(S_n)).\end{split}\]</div><p>The definition <code class="docutils literal notranslate"><span class="pre">sbSet</span></code> corresponds to the set <span class="math notranslate nohighlight">\(A = \bigcup_{n \in \mathbb{N}} S_n\)</span> in our proof sketch. The function <span class="math notranslate nohighlight">\(h\)</span> described above is now defined as follows:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">sbFun</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">β</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">sbSet</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="k">then</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="n">invFun</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">x</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">sbFun</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">α</span><span class="o">)</span> <span class="o">:</span> <span class="n">β</span> <span class="o">:=</span> <span class="k">if</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">sbSet</span> <span class="n">f</span> <span class="n">g</span> <span class="k">then</span> <span class="n">f</span> <span class="n">x</span> <span class="k">else</span> <span class="n">invFun</span> <span class="n">g</span> <span class="n">x</span> </pre></div> </div> <p>We will need the fact that our definition of <span class="math notranslate nohighlight">\(g^{-1}\)</span> is a
-
@@ -1008,16 +1001,16 @@ and fill in the remaining parts.You will need to use <code class="docutils literal notranslate"><span class="pre">invFun_eq</span></code> at the end. Notice that rewriting with <code class="docutils literal notranslate"><span class="pre">sbAux</span></code> here replaces <code class="docutils literal notranslate"><span class="pre">sbAux</span> <span class="pre">f</span> <span class="pre">g</span> <span class="pre">0</span></code> with the right-hand side of the corresponding defining equation.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">sb_right_inv</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hx</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∉</span><span class="w"> </span><span class="n">sbSet</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="o">(</span><span class="n">invFun</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="n">univ</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">contrapose</span><span class="bp">!</span><span class="w"> </span><span class="n">hx</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">sbSet</span><span class="o">,</span><span class="w"> </span><span class="n">mem_iUnion</span><span class="o">]</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="mi">0</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">sbAux</span><span class="o">,</span><span class="w"> </span><span class="n">mem_diff</span><span class="o">]</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">y</span><span class="o">,</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">sb_right_inv</span> <span class="o">{</span><span class="n">x</span> <span class="o">:</span> <span class="n">α</span><span class="o">}</span> <span class="o">(</span><span class="n">hx</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">∉</span> <span class="n">sbSet</span> <span class="n">f</span> <span class="n">g</span><span class="o">)</span> <span class="o">:</span> <span class="n">g</span> <span class="o">(</span><span class="n">invFun</span> <span class="n">g</span> <span class="n">x</span><span class="o">)</span> <span class="bp">=</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="k">have</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">g</span> <span class="bp">''</span> <span class="n">univ</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">contrapose</span><span class="bp">!</span> <span class="n">hx</span> <span class="n">rw</span> <span class="o">[</span><span class="n">sbSet</span><span class="o">,</span> <span class="n">mem_iUnion</span><span class="o">]</span> <span class="n">use</span> <span class="mi">0</span> <span class="n">rw</span> <span class="o">[</span><span class="n">sbAux</span><span class="o">,</span> <span class="n">mem_diff</span><span class="o">]</span> <span class="gr">sorry</span> <span class="k">have</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">y</span><span class="o">,</span> <span class="n">g</span> <span class="n">y</span> <span class="bp">=</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="gr">sorry</span> </pre></div> </div> <p>We now turn to the proof that <span class="math notranslate nohighlight">\(h\)</span> is injective.
-
@@ -1041,32 +1034,32 @@ Applying <span class="math notranslate nohighlight">\(g\)</span> to both sides y<p>Once again, we encourage you to step through the following proof to see how the argument plays out in Lean. See if you can finish off the proof using <code class="docutils literal notranslate"><span class="pre">sb_right_inv</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">sb_injective</span><span class="w"> </span><span class="o">(</span><span class="n">hf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Injective</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Injective</span><span class="w"> </span><span class="o">(</span><span class="n">sbFun</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">set</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">sbSet</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="n">A_def</span> <span class="w"> </span><span class="n">set</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">sbFun</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="n">h_def</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">x₁</span><span class="w"> </span><span class="n">x₂</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="o">(</span><span class="n">hxeq</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="n">x₁</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="n">x₂</span><span class="o">)</span> <span class="w"> </span><span class="k">show</span><span class="w"> </span><span class="n">x₁</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x₂</span> <span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="n">only</span><span class="w"> </span><span class="o">[</span><span class="n">h_def</span><span class="o">,</span><span class="w"> </span><span class="n">sbFun</span><span class="o">,</span><span class="w"> </span><span class="bp">←</span><span class="w"> </span><span class="n">A_def</span><span class="o">]</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">hxeq</span> <span class="w"> </span><span class="n">by_cases</span><span class="w"> </span><span class="n">xA</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x₁</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="bp">∨</span><span class="w"> </span><span class="n">x₂</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">A</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">wlog</span><span class="w"> </span><span class="n">x₁A</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x₁</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="n">generalizing</span><span class="w"> </span><span class="n">x₁</span><span class="w"> </span><span class="n">x₂</span><span class="w"> </span><span class="n">hxeq</span><span class="w"> </span><span class="n">xA</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">symm</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">this</span><span class="w"> </span><span class="n">hxeq.symm</span><span class="w"> </span><span class="n">xA.symm</span><span class="w"> </span><span class="o">(</span><span class="n">xA.resolve_left</span><span class="w"> </span><span class="n">x₁A</span><span class="o">)</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">x₂A</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x₂</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">_root_.not_imp_self.mp</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="o">(</span><span class="n">x₂nA</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x₂</span><span class="w"> </span><span class="bp">∉</span><span class="w"> </span><span class="n">A</span><span class="o">)</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">if_pos</span><span class="w"> </span><span class="n">x₁A</span><span class="o">,</span><span class="w"> </span><span class="n">if_neg</span><span class="w"> </span><span class="n">x₂nA</span><span class="o">]</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">hxeq</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">A_def</span><span class="o">,</span><span class="w"> </span><span class="n">sbSet</span><span class="o">,</span><span class="w"> </span><span class="n">mem_iUnion</span><span class="o">]</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">x₁A</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">x₂eq</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x₂</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">x₁</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">x₁A</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="n">hn</span><span class="o">⟩</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">A_def</span><span class="o">,</span><span class="w"> </span><span class="n">sbSet</span><span class="o">,</span><span class="w"> </span><span class="n">mem_iUnion</span><span class="o">]</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span> <span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="o">[</span><span class="n">sbAux</span><span class="o">]</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="o">⟨</span><span class="n">x₁</span><span class="o">,</span><span class="w"> </span><span class="n">hn</span><span class="o">,</span><span class="w"> </span><span class="n">x₂eq.symm</span><span class="o">⟩</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">push_neg</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">xA</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">sb_injective</span> <span class="o">(</span><span class="n">hf</span> <span class="o">:</span> <span class="n">Injective</span> <span class="n">f</span><span class="o">)</span> <span class="o">:</span> <span class="n">Injective</span> <span class="o">(</span><span class="n">sbFun</span> <span class="n">f</span> <span class="n">g</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">set</span> <span class="n">A</span> <span class="o">:=</span> <span class="n">sbSet</span> <span class="n">f</span> <span class="n">g</span> <span class="k">with</span> <span class="n">A_def</span> <span class="n">set</span> <span class="n">h</span> <span class="o">:=</span> <span class="n">sbFun</span> <span class="n">f</span> <span class="n">g</span> <span class="k">with</span> <span class="n">h_def</span> <span class="n">intro</span> <span class="n">x₁</span> <span class="n">x₂</span> <span class="n">intro</span> <span class="o">(</span><span class="n">hxeq</span> <span class="o">:</span> <span class="n">h</span> <span class="n">x₁</span> <span class="bp">=</span> <span class="n">h</span> <span class="n">x₂</span><span class="o">)</span> <span class="k">show</span> <span class="n">x₁</span> <span class="bp">=</span> <span class="n">x₂</span> <span class="n">simp</span> <span class="n">only</span> <span class="o">[</span><span class="n">h_def</span><span class="o">,</span> <span class="n">sbFun</span><span class="o">,</span> <span class="bp">←</span> <span class="n">A_def</span><span class="o">]</span> <span class="n">at</span> <span class="n">hxeq</span> <span class="n">by_cases</span> <span class="n">xA</span> <span class="o">:</span> <span class="n">x₁</span> <span class="bp">∈</span> <span class="n">A</span> <span class="bp">∨</span> <span class="n">x₂</span> <span class="bp">∈</span> <span class="n">A</span> <span class="bp">·</span> <span class="n">wlog</span> <span class="n">x₁A</span> <span class="o">:</span> <span class="n">x₁</span> <span class="bp">∈</span> <span class="n">A</span> <span class="n">generalizing</span> <span class="n">x₁</span> <span class="n">x₂</span> <span class="n">hxeq</span> <span class="n">xA</span> <span class="bp">·</span> <span class="n">symm</span> <span class="n">apply</span> <span class="n">this</span> <span class="n">hxeq.symm</span> <span class="n">xA.symm</span> <span class="o">(</span><span class="n">xA.resolve_left</span> <span class="n">x₁A</span><span class="o">)</span> <span class="k">have</span> <span class="n">x₂A</span> <span class="o">:</span> <span class="n">x₂</span> <span class="bp">∈</span> <span class="n">A</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">apply</span> <span class="n">_root_.not_imp_self.mp</span> <span class="n">intro</span> <span class="o">(</span><span class="n">x₂nA</span> <span class="o">:</span> <span class="n">x₂</span> <span class="bp">∉</span> <span class="n">A</span><span class="o">)</span> <span class="n">rw</span> <span class="o">[</span><span class="n">if_pos</span> <span class="n">x₁A</span><span class="o">,</span> <span class="n">if_neg</span> <span class="n">x₂nA</span><span class="o">]</span> <span class="n">at</span> <span class="n">hxeq</span> <span class="n">rw</span> <span class="o">[</span><span class="n">A_def</span><span class="o">,</span> <span class="n">sbSet</span><span class="o">,</span> <span class="n">mem_iUnion</span><span class="o">]</span> <span class="n">at</span> <span class="n">x₁A</span> <span class="k">have</span> <span class="n">x₂eq</span> <span class="o">:</span> <span class="n">x₂</span> <span class="bp">=</span> <span class="n">g</span> <span class="o">(</span><span class="n">f</span> <span class="n">x₁</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="n">rcases</span> <span class="n">x₁A</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">n</span><span class="o">,</span> <span class="n">hn</span><span class="o">⟩</span> <span class="n">rw</span> <span class="o">[</span><span class="n">A_def</span><span class="o">,</span> <span class="n">sbSet</span><span class="o">,</span> <span class="n">mem_iUnion</span><span class="o">]</span> <span class="n">use</span> <span class="n">n</span> <span class="bp">+</span> <span class="mi">1</span> <span class="n">simp</span> <span class="o">[</span><span class="n">sbAux</span><span class="o">]</span> <span class="n">exact</span> <span class="o">⟨</span><span class="n">x₁</span><span class="o">,</span> <span class="n">hn</span><span class="o">,</span> <span class="n">x₂eq.symm</span><span class="o">⟩</span> <span class="gr">sorry</span> <span class="n">push_neg</span> <span class="n">at</span> <span class="n">xA</span> <span class="gr">sorry</span> </pre></div> </div> <p>The proof introduces some new tactics.
-
@@ -1100,32 +1093,32 @@ The tactic <code class="docutils literal notranslate"><span class="pre">rcases</and <code class="docutils literal notranslate"><span class="pre">g</span> <span class="pre">y</span> <span class="pre">∈</span> <span class="pre">sbAux</span> <span class="pre">f</span> <span class="pre">g</span> <span class="pre">(n</span> <span class="pre">+</span> <span class="pre">1)</span></code>. In both cases, calling the simplifier with <code class="docutils literal notranslate"><span class="pre">simp</span> <span class="pre">[sbAux]</span></code> applies the corresponding defining equation of <code class="docutils literal notranslate"><span class="pre">sbAux</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">sb_surjective</span><span class="w"> </span><span class="o">(</span><span class="n">hg</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Injective</span><span class="w"> </span><span class="n">g</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Surjective</span><span class="w"> </span><span class="o">(</span><span class="n">sbFun</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">set</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">sbSet</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="n">A_def</span> <span class="w"> </span><span class="n">set</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">sbFun</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="n">h_def</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">y</span> <span class="w"> </span><span class="n">by_cases</span><span class="w"> </span><span class="n">gyA</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">A</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">A_def</span><span class="o">,</span><span class="w"> </span><span class="n">sbSet</span><span class="o">,</span><span class="w"> </span><span class="n">mem_iUnion</span><span class="o">]</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">gyA</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">gyA</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="n">hn</span><span class="o">⟩</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">n</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="o">[</span><span class="n">sbAux</span><span class="o">]</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">hn</span> <span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="o">[</span><span class="n">sbAux</span><span class="o">]</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">hn</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">hn</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">xmem</span><span class="o">,</span><span class="w"> </span><span class="n">hx</span><span class="o">⟩</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">x</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">A_def</span><span class="o">,</span><span class="w"> </span><span class="n">sbSet</span><span class="o">,</span><span class="w"> </span><span class="n">mem_iUnion</span><span class="o">]</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="o">⟨</span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="n">xmem</span><span class="o">⟩</span> <span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="n">only</span><span class="w"> </span><span class="o">[</span><span class="n">h_def</span><span class="o">,</span><span class="w"> </span><span class="n">sbFun</span><span class="o">,</span><span class="w"> </span><span class="n">if_pos</span><span class="w"> </span><span class="n">this</span><span class="o">]</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">hg</span><span class="w"> </span><span class="n">hx</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">sb_surjective</span> <span class="o">(</span><span class="n">hg</span> <span class="o">:</span> <span class="n">Injective</span> <span class="n">g</span><span class="o">)</span> <span class="o">:</span> <span class="n">Surjective</span> <span class="o">(</span><span class="n">sbFun</span> <span class="n">f</span> <span class="n">g</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">set</span> <span class="n">A</span> <span class="o">:=</span> <span class="n">sbSet</span> <span class="n">f</span> <span class="n">g</span> <span class="k">with</span> <span class="n">A_def</span> <span class="n">set</span> <span class="n">h</span> <span class="o">:=</span> <span class="n">sbFun</span> <span class="n">f</span> <span class="n">g</span> <span class="k">with</span> <span class="n">h_def</span> <span class="n">intro</span> <span class="n">y</span> <span class="n">by_cases</span> <span class="n">gyA</span> <span class="o">:</span> <span class="n">g</span> <span class="n">y</span> <span class="bp">∈</span> <span class="n">A</span> <span class="bp">·</span> <span class="n">rw</span> <span class="o">[</span><span class="n">A_def</span><span class="o">,</span> <span class="n">sbSet</span><span class="o">,</span> <span class="n">mem_iUnion</span><span class="o">]</span> <span class="n">at</span> <span class="n">gyA</span> <span class="n">rcases</span> <span class="n">gyA</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">n</span><span class="o">,</span> <span class="n">hn</span><span class="o">⟩</span> <span class="n">rcases</span> <span class="n">n</span> <span class="k">with</span> <span class="n">_</span> <span class="bp">|</span> <span class="n">n</span> <span class="bp">·</span> <span class="n">simp</span> <span class="o">[</span><span class="n">sbAux</span><span class="o">]</span> <span class="n">at</span> <span class="n">hn</span> <span class="n">simp</span> <span class="o">[</span><span class="n">sbAux</span><span class="o">]</span> <span class="n">at</span> <span class="n">hn</span> <span class="n">rcases</span> <span class="n">hn</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">x</span><span class="o">,</span> <span class="n">xmem</span><span class="o">,</span> <span class="n">hx</span><span class="o">⟩</span> <span class="n">use</span> <span class="n">x</span> <span class="k">have</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">A</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">A_def</span><span class="o">,</span> <span class="n">sbSet</span><span class="o">,</span> <span class="n">mem_iUnion</span><span class="o">]</span> <span class="n">exact</span> <span class="o">⟨</span><span class="n">n</span><span class="o">,</span> <span class="n">xmem</span><span class="o">⟩</span> <span class="n">simp</span> <span class="n">only</span> <span class="o">[</span><span class="n">h_def</span><span class="o">,</span> <span class="n">sbFun</span><span class="o">,</span> <span class="n">if_pos</span> <span class="n">this</span><span class="o">]</span> <span class="n">exact</span> <span class="n">hg</span> <span class="n">hx</span> <span class="gr">sorry</span> </pre></div> </div> <p>We can now put it all together. The final statement is short and sweet, and the proof uses the fact that <code class="docutils literal notranslate"><span class="pre">Bijective</span> <span class="pre">h</span></code> unfolds to <code class="docutils literal notranslate"><span class="pre">Injective</span> <span class="pre">h</span> <span class="pre">∧</span> <span class="pre">Surjective</span> <span class="pre">h</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">schroeder_bernstein</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">β</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">g</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">β</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">α</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Injective</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hg</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Injective</span><span class="w"> </span><span class="n">g</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">β</span><span class="o">,</span><span class="w"> </span><span class="n">Bijective</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">⟨</span><span class="n">sbFun</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="o">,</span><span class="w"> </span><span class="n">sb_injective</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">hf</span><span class="o">,</span><span class="w"> </span><span class="n">sb_surjective</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">hg</span><span class="o">⟩</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">schroeder_bernstein</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">β</span><span class="o">}</span> <span class="o">{</span><span class="n">g</span> <span class="o">:</span> <span class="n">β</span> <span class="bp">→</span> <span class="n">α</span><span class="o">}</span> <span class="o">(</span><span class="n">hf</span> <span class="o">:</span> <span class="n">Injective</span> <span class="n">f</span><span class="o">)</span> <span class="o">(</span><span class="n">hg</span> <span class="o">:</span> <span class="n">Injective</span> <span class="n">g</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">h</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">β</span><span class="o">,</span> <span class="n">Bijective</span> <span class="n">h</span> <span class="o">:=</span> <span class="o">⟨</span><span class="n">sbFun</span> <span class="n">f</span> <span class="n">g</span><span class="o">,</span> <span class="n">sb_injective</span> <span class="n">f</span> <span class="n">g</span> <span class="n">hf</span><span class="o">,</span> <span class="n">sb_surjective</span> <span class="n">f</span> <span class="n">g</span> <span class="n">hg</span><span class="o">⟩</span> </pre></div> </div> </section>
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@@ -93,14 +89,14 @@<div itemprop="articleBody"> <section id="elementary-number-theory"> <span id="number-theory"></span><h1><span class="section-number">5. </span>Elementary Number Theory<a class="headerlink" href="#elementary-number-theory" title="Link to this heading"></a></h1> <span id="number-theory"></span><h1><span class="section-number">5. </span>Elementary Number Theory<a class="headerlink" href="#elementary-number-theory" title="Permalink to this heading"></a></h1> <p>In this chapter, we show you how to formalize some elementary results in number theory. As we deal with more substantive mathematical content, the proofs will get longer and more involved, building on the skills you have already mastered.</p> <section id="irrational-roots"> <span id="section-irrational-roots"></span><h2><span class="section-number">5.1. </span>Irrational Roots<a class="headerlink" href="#irrational-roots" title="Link to this heading"></a></h2> <span id="section-irrational-roots"></span><h2><span class="section-number">5.1. </span>Irrational Roots<a class="headerlink" href="#irrational-roots" title="Permalink to this heading"></a></h2> <p>Let’s start with a fact known to the ancient Greeks, namely, that the square root of 2 is irrational. If we suppose otherwise,
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@@ -124,18 +120,18 @@ when necessary,but we can also do it manually by rewriting or simplifying with the identifier <code class="docutils literal notranslate"><span class="pre">Nat.Coprime</span></code>. The <code class="docutils literal notranslate"><span class="pre">norm_num</span></code> tactic is smart enough to compute concrete values.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#print</span><span class="w"> </span><span class="n">Nat.Coprime</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#print</span> <span class="n">Nat.Coprime</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m.Coprime</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m.gcd</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">h</span> <span class="kd">example</span> <span class="o">(</span><span class="n">m</span> <span class="n">n</span> <span class="o">:</span> <span class="n">Nat</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">m.Coprime</span> <span class="n">n</span><span class="o">)</span> <span class="o">:</span> <span class="n">m.gcd</span> <span class="n">n</span> <span class="bp">=</span> <span class="mi">1</span> <span class="o">:=</span> <span class="n">h</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m.Coprime</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m.gcd</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">Nat.Coprime</span><span class="o">]</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">h</span> <span class="kd">example</span> <span class="o">(</span><span class="n">m</span> <span class="n">n</span> <span class="o">:</span> <span class="n">Nat</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">m.Coprime</span> <span class="n">n</span><span class="o">)</span> <span class="o">:</span> <span class="n">m.gcd</span> <span class="n">n</span> <span class="bp">=</span> <span class="mi">1</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">Nat.Coprime</span><span class="o">]</span> <span class="n">at</span> <span class="n">h</span> <span class="n">exact</span> <span class="n">h</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat.Coprime</span><span class="w"> </span><span class="mi">12</span><span class="w"> </span><span class="mi">7</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">norm_num</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">Nat.Coprime</span> <span class="mi">12</span> <span class="mi">7</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">norm_num</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat.gcd</span><span class="w"> </span><span class="mi">12</span><span class="w"> </span><span class="mi">8</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">norm_num</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">Nat.gcd</span> <span class="mi">12</span> <span class="mi">8</span> <span class="bp">=</span> <span class="mi">4</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">norm_num</span> </pre></div> </div> <p>We have already encountered the <code class="docutils literal notranslate"><span class="pre">gcd</span></code> function in
-
@@ -153,24 +149,24 @@ to the natural numbers.</p><p>We also need the notion of a prime number, <code class="docutils literal notranslate"><span class="pre">Nat.Prime</span></code>. The theorem <code class="docutils literal notranslate"><span class="pre">Nat.prime_def_lt</span></code> provides one familiar characterization, and <code class="docutils literal notranslate"><span class="pre">Nat.Prime.eq_one_or_self_of_dvd</span></code> provides another.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="n">Nat.prime_def_lt</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="n">Nat.prime_def_lt</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">p</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">prime_p</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat.Prime</span><span class="w"> </span><span class="n">p</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">,</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rwa</span><span class="w"> </span><span class="o">[</span><span class="n">Nat.prime_def_lt</span><span class="o">]</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">prime_p</span> <span class="kd">example</span> <span class="o">(</span><span class="n">p</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">(</span><span class="n">prime_p</span> <span class="o">:</span> <span class="n">Nat.Prime</span> <span class="n">p</span><span class="o">)</span> <span class="o">:</span> <span class="mi">2</span> <span class="bp">≤</span> <span class="n">p</span> <span class="bp">∧</span> <span class="bp">∀</span> <span class="n">m</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">,</span> <span class="n">m</span> <span class="bp"><</span> <span class="n">p</span> <span class="bp">→</span> <span class="n">m</span> <span class="bp">∣</span> <span class="n">p</span> <span class="bp">→</span> <span class="n">m</span> <span class="bp">=</span> <span class="mi">1</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rwa</span> <span class="o">[</span><span class="n">Nat.prime_def_lt</span><span class="o">]</span> <span class="n">at</span> <span class="n">prime_p</span> <span class="k">#check</span><span class="w"> </span><span class="n">Nat.Prime.eq_one_or_self_of_dvd</span> <span class="k">#check</span> <span class="n">Nat.Prime.eq_one_or_self_of_dvd</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">p</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">prime_p</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat.Prime</span><span class="w"> </span><span class="n">p</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">,</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">∨</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">prime_p.eq_one_or_self_of_dvd</span> <span class="kd">example</span> <span class="o">(</span><span class="n">p</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">(</span><span class="n">prime_p</span> <span class="o">:</span> <span class="n">Nat.Prime</span> <span class="n">p</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">m</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">,</span> <span class="n">m</span> <span class="bp">∣</span> <span class="n">p</span> <span class="bp">→</span> <span class="n">m</span> <span class="bp">=</span> <span class="mi">1</span> <span class="bp">∨</span> <span class="n">m</span> <span class="bp">=</span> <span class="n">p</span> <span class="o">:=</span> <span class="n">prime_p.eq_one_or_self_of_dvd</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat.Prime</span><span class="w"> </span><span class="mi">17</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">norm_num</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">Nat.Prime</span> <span class="mi">17</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">norm_num</span> <span class="c1">-- commonly used</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat.Prime</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Nat.prime_two</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">Nat.Prime</span> <span class="mi">2</span> <span class="o">:=</span> <span class="n">Nat.prime_two</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat.Prime</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Nat.prime_three</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">Nat.Prime</span> <span class="mi">3</span> <span class="o">:=</span> <span class="n">Nat.prime_three</span> </pre></div> </div> <p>In the natural numbers, a prime number has the property that it cannot
-
@@ -188,16 +184,16 @@ if the square of a number is even, then that number is even as well.Mathlib defines the predicate <code class="docutils literal notranslate"><span class="pre">Even</span></code> in <code class="docutils literal notranslate"><span class="pre">Algebra.Group.Even</span></code>, but for reasons that will become clear below, we will simply use <code class="docutils literal notranslate"><span class="pre">2</span> <span class="pre">∣</span> <span class="pre">m</span></code> to express that <code class="docutils literal notranslate"><span class="pre">m</span></code> is even.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="n">Nat.Prime.dvd_mul</span> <span class="k">#check</span><span class="w"> </span><span class="n">Nat.Prime.dvd_mul</span><span class="w"> </span><span class="n">Nat.prime_two</span> <span class="k">#check</span><span class="w"> </span><span class="n">Nat.prime_two.dvd_mul</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="n">Nat.Prime.dvd_mul</span> <span class="k">#check</span> <span class="n">Nat.Prime.dvd_mul</span> <span class="n">Nat.prime_two</span> <span class="k">#check</span> <span class="n">Nat.prime_two.dvd_mul</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">even_of_even_sqr</span><span class="w"> </span><span class="o">{</span><span class="n">m</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">pow_two</span><span class="o">,</span><span class="w"> </span><span class="n">Nat.prime_two.dvd_mul</span><span class="o">]</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="n">cases</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">assumption</span> <span class="kd">theorem</span> <span class="n">even_of_even_sqr</span> <span class="o">{</span><span class="n">m</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="mi">2</span> <span class="bp">∣</span> <span class="n">m</span> <span class="bp">^</span> <span class="mi">2</span><span class="o">)</span> <span class="o">:</span> <span class="mi">2</span> <span class="bp">∣</span> <span class="n">m</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">pow_two</span><span class="o">,</span> <span class="n">Nat.prime_two.dvd_mul</span><span class="o">]</span> <span class="n">at</span> <span class="n">h</span> <span class="n">cases</span> <span class="n">h</span> <span class="bp"><;></span> <span class="n">assumption</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">m</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Nat.Prime.dvd_of_dvd_pow</span><span class="w"> </span><span class="n">Nat.prime_two</span><span class="w"> </span><span class="n">h</span> <span class="kd">example</span> <span class="o">{</span><span class="n">m</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="mi">2</span> <span class="bp">∣</span> <span class="n">m</span> <span class="bp">^</span> <span class="mi">2</span><span class="o">)</span> <span class="o">:</span> <span class="mi">2</span> <span class="bp">∣</span> <span class="n">m</span> <span class="o">:=</span> <span class="n">Nat.Prime.dvd_of_dvd_pow</span> <span class="n">Nat.prime_two</span> <span class="n">h</span> </pre></div> </div> <p>As we proceed, you will need to become proficient at finding the facts you
-
@@ -214,32 +210,32 @@ You can also use the search engine on theand if all else fails, don’t hesitate to ask on <a class="reference external" href="https://leanprover.zulipchat.com/">Zulip</a>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="c1">-- apply? suggests the following:</span> <span class="w"> </span><span class="o">(</span><span class="n">mul_right_inj'</span><span class="w"> </span><span class="n">h'</span><span class="o">)</span><span class="bp">.</span><span class="n">mp</span><span class="w"> </span><span class="n">h</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">Nat</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">c</span><span class="o">)</span> <span class="o">(</span><span class="n">h'</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">≠</span> <span class="mi">0</span><span class="o">)</span> <span class="o">:</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">c</span> <span class="o">:=</span> <span class="c1">-- apply? suggests the following:</span> <span class="o">(</span><span class="n">mul_right_inj'</span> <span class="n">h'</span><span class="o">)</span><span class="bp">.</span><span class="n">mp</span> <span class="n">h</span> </pre></div> </div> <p>The heart of our proof of the irrationality of the square root of two is contained in the following theorem. See if you can fill out the proof sketch, using <code class="docutils literal notranslate"><span class="pre">even_of_even_sqr</span></code> and the theorem <code class="docutils literal notranslate"><span class="pre">Nat.dvd_gcd</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">coprime_mn</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m.Coprime</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">sqr_eq</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">obtain</span><span class="w"> </span><span class="o">⟨</span><span class="n">k</span><span class="o">,</span><span class="w"> </span><span class="n">meq</span><span class="o">⟩</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">dvd_iff_exists_eq_mul_left.mp</span><span class="w"> </span><span class="n">this</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="mi">2</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">k</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="bp">←</span><span class="w"> </span><span class="n">sqr_eq</span><span class="o">,</span><span class="w"> </span><span class="n">meq</span><span class="o">]</span> <span class="w"> </span><span class="n">ring</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">k</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">m.gcd</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">norm_num</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">this</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">m</span> <span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">}</span> <span class="o">(</span><span class="n">coprime_mn</span> <span class="o">:</span> <span class="n">m.Coprime</span> <span class="n">n</span><span class="o">)</span> <span class="o">:</span> <span class="n">m</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">≠</span> <span class="mi">2</span> <span class="bp">*</span> <span class="n">n</span> <span class="bp">^</span> <span class="mi">2</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">sqr_eq</span> <span class="k">have</span> <span class="o">:</span> <span class="mi">2</span> <span class="bp">∣</span> <span class="n">m</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="n">obtain</span> <span class="o">⟨</span><span class="n">k</span><span class="o">,</span> <span class="n">meq</span><span class="o">⟩</span> <span class="o">:=</span> <span class="n">dvd_iff_exists_eq_mul_left.mp</span> <span class="n">this</span> <span class="k">have</span> <span class="o">:</span> <span class="mi">2</span> <span class="bp">*</span> <span class="o">(</span><span class="mi">2</span> <span class="bp">*</span> <span class="n">k</span> <span class="bp">^</span> <span class="mi">2</span><span class="o">)</span> <span class="bp">=</span> <span class="mi">2</span> <span class="bp">*</span> <span class="n">n</span> <span class="bp">^</span> <span class="mi">2</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="bp">←</span> <span class="n">sqr_eq</span><span class="o">,</span> <span class="n">meq</span><span class="o">]</span> <span class="n">ring</span> <span class="k">have</span> <span class="o">:</span> <span class="mi">2</span> <span class="bp">*</span> <span class="n">k</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">=</span> <span class="n">n</span> <span class="bp">^</span> <span class="mi">2</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="k">have</span> <span class="o">:</span> <span class="mi">2</span> <span class="bp">∣</span> <span class="n">n</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="k">have</span> <span class="o">:</span> <span class="mi">2</span> <span class="bp">∣</span> <span class="n">m.gcd</span> <span class="n">n</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="k">have</span> <span class="o">:</span> <span class="mi">2</span> <span class="bp">∣</span> <span class="mi">1</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="n">norm_num</span> <span class="n">at</span> <span class="n">this</span> </pre></div> </div> <p>In fact, with very few changes, we can replace <code class="docutils literal notranslate"><span class="pre">2</span></code> by an arbitrary prime.
-
@@ -249,8 +245,8 @@ At the end of the proof, you’ll need to derive a contradiction fromYou can use <code class="docutils literal notranslate"><span class="pre">Nat.Prime.two_le</span></code>, which says that any prime number is greater than or equal to two, and <code class="docutils literal notranslate"><span class="pre">Nat.le_of_dvd</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">coprime_mn</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m.Coprime</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">prime_p</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">p.Prime</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">m</span> <span class="n">n</span> <span class="n">p</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">}</span> <span class="o">(</span><span class="n">coprime_mn</span> <span class="o">:</span> <span class="n">m.Coprime</span> <span class="n">n</span><span class="o">)</span> <span class="o">(</span><span class="n">prime_p</span> <span class="o">:</span> <span class="n">p.Prime</span><span class="o">)</span> <span class="o">:</span> <span class="n">m</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">≠</span> <span class="n">p</span> <span class="bp">*</span> <span class="n">n</span> <span class="bp">^</span> <span class="mi">2</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>Let us consider another approach.
-
@@ -272,10 +268,10 @@ are prime, that any <code class="docutils literal notranslate"><span class="pre"product of its factors, and that if <code class="docutils literal notranslate"><span class="pre">n</span></code> is equal to the product of another list of prime numbers, then that list is a permutation of <code class="docutils literal notranslate"><span class="pre">Nat.primeFactorsList</span> <span class="pre">n</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="n">Nat.primeFactorsList</span> <span class="k">#check</span><span class="w"> </span><span class="n">Nat.prime_of_mem_primeFactorsList</span> <span class="k">#check</span><span class="w"> </span><span class="n">Nat.prod_primeFactorsList</span> <span class="k">#check</span><span class="w"> </span><span class="n">Nat.primeFactorsList_unique</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="n">Nat.primeFactorsList</span> <span class="k">#check</span> <span class="n">Nat.prime_of_mem_primeFactorsList</span> <span class="k">#check</span> <span class="n">Nat.prod_primeFactorsList</span> <span class="k">#check</span> <span class="n">Nat.primeFactorsList_unique</span> </pre></div> </div> <p>You can browse these theorems and others nearby, even though we have not
-
@@ -286,20 +282,20 @@ that represents the same data as a function.Specifically, <code class="docutils literal notranslate"><span class="pre">Nat.factorization</span> <span class="pre">n</span> <span class="pre">p</span></code>, which we can also write <code class="docutils literal notranslate"><span class="pre">n.factorization</span> <span class="pre">p</span></code>, returns the multiplicity of <code class="docutils literal notranslate"><span class="pre">p</span></code> in the prime factorization of <code class="docutils literal notranslate"><span class="pre">n</span></code>. We will use the following three facts.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">factorization_mul'</span><span class="w"> </span><span class="o">{</span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">mnez</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">nnez</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">p</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="o">(</span><span class="n">m</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="bp">.</span><span class="n">factorization</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">m.factorization</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">n.factorization</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">Nat.factorization_mul</span><span class="w"> </span><span class="n">mnez</span><span class="w"> </span><span class="n">nnez</span><span class="o">]</span> <span class="w"> </span><span class="n">rfl</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">factorization_mul'</span> <span class="o">{</span><span class="n">m</span> <span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">}</span> <span class="o">(</span><span class="n">mnez</span> <span class="o">:</span> <span class="n">m</span> <span class="bp">≠</span> <span class="mi">0</span><span class="o">)</span> <span class="o">(</span><span class="n">nnez</span> <span class="o">:</span> <span class="n">n</span> <span class="bp">≠</span> <span class="mi">0</span><span class="o">)</span> <span class="o">(</span><span class="n">p</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">m</span> <span class="bp">*</span> <span class="n">n</span><span class="o">)</span><span class="bp">.</span><span class="n">factorization</span> <span class="n">p</span> <span class="bp">=</span> <span class="n">m.factorization</span> <span class="n">p</span> <span class="bp">+</span> <span class="n">n.factorization</span> <span class="n">p</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">Nat.factorization_mul</span> <span class="n">mnez</span> <span class="n">nnez</span><span class="o">]</span> <span class="n">rfl</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">factorization_pow'</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="n">k</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="n">k</span><span class="o">)</span><span class="bp">.</span><span class="n">factorization</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">k</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">n.factorization</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">Nat.factorization_pow</span><span class="o">]</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">theorem</span> <span class="n">factorization_pow'</span> <span class="o">(</span><span class="n">n</span> <span class="n">k</span> <span class="n">p</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">n</span> <span class="bp">^</span> <span class="n">k</span><span class="o">)</span><span class="bp">.</span><span class="n">factorization</span> <span class="n">p</span> <span class="bp">=</span> <span class="n">k</span> <span class="bp">*</span> <span class="n">n.factorization</span> <span class="n">p</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">Nat.factorization_pow</span><span class="o">]</span> <span class="n">rfl</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">Nat.Prime.factorization'</span><span class="w"> </span><span class="o">{</span><span class="n">p</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">prime_p</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">p.Prime</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">p.factorization</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">prime_p.factorization</span><span class="o">]</span> <span class="w"> </span><span class="n">simp</span> <span class="kd">theorem</span> <span class="n">Nat.Prime.factorization'</span> <span class="o">{</span><span class="n">p</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">}</span> <span class="o">(</span><span class="n">prime_p</span> <span class="o">:</span> <span class="n">p.Prime</span><span class="o">)</span> <span class="o">:</span> <span class="n">p.factorization</span> <span class="n">p</span> <span class="bp">=</span> <span class="mi">1</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">prime_p.factorization</span><span class="o">]</span> <span class="n">simp</span> </pre></div> </div> <p>In fact, <code class="docutils literal notranslate"><span class="pre">n.factorization</span></code> is defined in Lean as a function of finite support,
-
@@ -311,17 +307,17 @@ the three theorems above as a black box.</p>followed by <code class="docutils literal notranslate"><span class="pre">assumption</span></code>.</p> <p>See if you can use the identities above to fill in the missing parts of the proof.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">nnz</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">prime_p</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">p.Prime</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">sqr_eq</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">nsqr_nez</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">simpa</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">eq1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat.factorization</span><span class="w"> </span><span class="o">(</span><span class="n">m</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">m.factorization</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">eq2</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">p</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="o">)</span><span class="bp">.</span><span class="n">factorization</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">n.factorization</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">m.factorization</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">%</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">(</span><span class="mi">2</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">n.factorization</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="bp">%</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="bp">←</span><span class="w"> </span><span class="n">eq1</span><span class="o">,</span><span class="w"> </span><span class="n">sqr_eq</span><span class="o">,</span><span class="w"> </span><span class="n">eq2</span><span class="o">]</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">add_comm</span><span class="o">,</span><span class="w"> </span><span class="n">Nat.add_mul_mod_self_left</span><span class="o">,</span><span class="w"> </span><span class="n">Nat.mul_mod_right</span><span class="o">]</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">this</span> <span class="w"> </span><span class="n">norm_num</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">this</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">m</span> <span class="n">n</span> <span class="n">p</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">}</span> <span class="o">(</span><span class="n">nnz</span> <span class="o">:</span> <span class="n">n</span> <span class="bp">≠</span> <span class="mi">0</span><span class="o">)</span> <span class="o">(</span><span class="n">prime_p</span> <span class="o">:</span> <span class="n">p.Prime</span><span class="o">)</span> <span class="o">:</span> <span class="n">m</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">≠</span> <span class="n">p</span> <span class="bp">*</span> <span class="n">n</span> <span class="bp">^</span> <span class="mi">2</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">sqr_eq</span> <span class="k">have</span> <span class="n">nsqr_nez</span> <span class="o">:</span> <span class="n">n</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">≠</span> <span class="mi">0</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simpa</span> <span class="k">have</span> <span class="n">eq1</span> <span class="o">:</span> <span class="n">Nat.factorization</span> <span class="o">(</span><span class="n">m</span> <span class="bp">^</span> <span class="mi">2</span><span class="o">)</span> <span class="n">p</span> <span class="bp">=</span> <span class="mi">2</span> <span class="bp">*</span> <span class="n">m.factorization</span> <span class="n">p</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="k">have</span> <span class="n">eq2</span> <span class="o">:</span> <span class="o">(</span><span class="n">p</span> <span class="bp">*</span> <span class="n">n</span> <span class="bp">^</span> <span class="mi">2</span><span class="o">)</span><span class="bp">.</span><span class="n">factorization</span> <span class="n">p</span> <span class="bp">=</span> <span class="mi">2</span> <span class="bp">*</span> <span class="n">n.factorization</span> <span class="n">p</span> <span class="bp">+</span> <span class="mi">1</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="k">have</span> <span class="o">:</span> <span class="mi">2</span> <span class="bp">*</span> <span class="n">m.factorization</span> <span class="n">p</span> <span class="bp">%</span> <span class="mi">2</span> <span class="bp">=</span> <span class="o">(</span><span class="mi">2</span> <span class="bp">*</span> <span class="n">n.factorization</span> <span class="n">p</span> <span class="bp">+</span> <span class="mi">1</span><span class="o">)</span> <span class="bp">%</span> <span class="mi">2</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="bp">←</span> <span class="n">eq1</span><span class="o">,</span> <span class="n">sqr_eq</span><span class="o">,</span> <span class="n">eq2</span><span class="o">]</span> <span class="n">rw</span> <span class="o">[</span><span class="n">add_comm</span><span class="o">,</span> <span class="n">Nat.add_mul_mod_self_left</span><span class="o">,</span> <span class="n">Nat.mul_mod_right</span><span class="o">]</span> <span class="n">at</span> <span class="n">this</span> <span class="n">norm_num</span> <span class="n">at</span> <span class="n">this</span> </pre></div> </div> <p>A nice thing about this proof is that it also generalizes. There is
-
@@ -348,20 +344,20 @@ to finish it off.</p><p>Note that this example does not assume that <code class="docutils literal notranslate"><span class="pre">p</span></code> is prime, but the conclusion is trivial when <code class="docutils literal notranslate"><span class="pre">p</span></code> is not prime since <code class="docutils literal notranslate"><span class="pre">r.factorization</span> <span class="pre">p</span></code> is then zero by definition, and the proof works in all cases anyway.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">k</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">nnz</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">pow_eq</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="n">k</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="n">k</span><span class="o">)</span><span class="w"> </span><span class="o">{</span><span class="n">p</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">}</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">k</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">r.factorization</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">r</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">simp</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">npow_nz</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="n">k</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">npowz</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">nnz</span><span class="w"> </span><span class="o">(</span><span class="n">pow_eq_zero</span><span class="w"> </span><span class="n">npowz</span><span class="o">)</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">eq1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">m</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="n">k</span><span class="o">)</span><span class="bp">.</span><span class="n">factorization</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">k</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">m.factorization</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">eq2</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">((</span><span class="n">r</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="n">k</span><span class="o">)</span><span class="bp">.</span><span class="n">factorization</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">=</span> <span class="w"> </span><span class="n">k</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">n.factorization</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="o">(</span><span class="n">r</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="bp">.</span><span class="n">factorization</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">r.succ.factorization</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">k</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">m.factorization</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">k</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">n.factorization</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="bp">←</span><span class="w"> </span><span class="n">eq1</span><span class="o">,</span><span class="w"> </span><span class="n">pow_eq</span><span class="o">,</span><span class="w"> </span><span class="n">eq2</span><span class="o">,</span><span class="w"> </span><span class="n">add_comm</span><span class="o">,</span><span class="w"> </span><span class="n">Nat.add_sub_cancel</span><span class="o">]</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">this</span><span class="o">]</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">m</span> <span class="n">n</span> <span class="n">k</span> <span class="n">r</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">}</span> <span class="o">(</span><span class="n">nnz</span> <span class="o">:</span> <span class="n">n</span> <span class="bp">≠</span> <span class="mi">0</span><span class="o">)</span> <span class="o">(</span><span class="n">pow_eq</span> <span class="o">:</span> <span class="n">m</span> <span class="bp">^</span> <span class="n">k</span> <span class="bp">=</span> <span class="n">r</span> <span class="bp">*</span> <span class="n">n</span> <span class="bp">^</span> <span class="n">k</span><span class="o">)</span> <span class="o">{</span><span class="n">p</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">}</span> <span class="o">:</span> <span class="n">k</span> <span class="bp">∣</span> <span class="n">r.factorization</span> <span class="n">p</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rcases</span> <span class="n">r</span> <span class="k">with</span> <span class="n">_</span> <span class="bp">|</span> <span class="n">r</span> <span class="bp">·</span> <span class="n">simp</span> <span class="k">have</span> <span class="n">npow_nz</span> <span class="o">:</span> <span class="n">n</span> <span class="bp">^</span> <span class="n">k</span> <span class="bp">≠</span> <span class="mi">0</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">npowz</span> <span class="bp">↦</span> <span class="n">nnz</span> <span class="o">(</span><span class="n">pow_eq_zero</span> <span class="n">npowz</span><span class="o">)</span> <span class="k">have</span> <span class="n">eq1</span> <span class="o">:</span> <span class="o">(</span><span class="n">m</span> <span class="bp">^</span> <span class="n">k</span><span class="o">)</span><span class="bp">.</span><span class="n">factorization</span> <span class="n">p</span> <span class="bp">=</span> <span class="n">k</span> <span class="bp">*</span> <span class="n">m.factorization</span> <span class="n">p</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="k">have</span> <span class="n">eq2</span> <span class="o">:</span> <span class="o">((</span><span class="n">r</span> <span class="bp">+</span> <span class="mi">1</span><span class="o">)</span> <span class="bp">*</span> <span class="n">n</span> <span class="bp">^</span> <span class="n">k</span><span class="o">)</span><span class="bp">.</span><span class="n">factorization</span> <span class="n">p</span> <span class="bp">=</span> <span class="n">k</span> <span class="bp">*</span> <span class="n">n.factorization</span> <span class="n">p</span> <span class="bp">+</span> <span class="o">(</span><span class="n">r</span> <span class="bp">+</span> <span class="mi">1</span><span class="o">)</span><span class="bp">.</span><span class="n">factorization</span> <span class="n">p</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="k">have</span> <span class="o">:</span> <span class="n">r.succ.factorization</span> <span class="n">p</span> <span class="bp">=</span> <span class="n">k</span> <span class="bp">*</span> <span class="n">m.factorization</span> <span class="n">p</span> <span class="bp">-</span> <span class="n">k</span> <span class="bp">*</span> <span class="n">n.factorization</span> <span class="n">p</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="bp">←</span> <span class="n">eq1</span><span class="o">,</span> <span class="n">pow_eq</span><span class="o">,</span> <span class="n">eq2</span><span class="o">,</span> <span class="n">add_comm</span><span class="o">,</span> <span class="n">Nat.add_sub_cancel</span><span class="o">]</span> <span class="n">rw</span> <span class="o">[</span><span class="n">this</span><span class="o">]</span> <span class="gr">sorry</span> </pre></div> </div> <p>There are a number of ways in which we might want to improve on these results.
-
@@ -403,7 +399,7 @@ In the next chapter, we will begin to develop the means toappreciate the way that Lean supports this sort of generality.</p> </section> <section id="induction-and-recursion"> <span id="section-induction-and-recursion"></span><h2><span class="section-number">5.2. </span>Induction and Recursion<a class="headerlink" href="#induction-and-recursion" title="Link to this heading"></a></h2> <span id="section-induction-and-recursion"></span><h2><span class="section-number">5.2. </span>Induction and Recursion<a class="headerlink" href="#induction-and-recursion" title="Permalink to this heading"></a></h2> <p>The set of natural numbers <span class="math notranslate nohighlight">\(\mathbb{N} = \{ 0, 1, 2, \ldots \}\)</span> is not only fundamentally important in its own right, but also a plays a central role in the construction of new mathematical objects.
-
@@ -411,9 +407,9 @@ Lean’s foundation allows us to declare <em>inductive types</em>,which are types generated inductively by a given list of <em>constructors</em>. In Lean, the natural numbers are declared as follows.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">inductive</span><span class="w"> </span><span class="n">Nat</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">zero</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat</span> <span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">succ</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">inductive</span> <span class="n">Nat</span> <span class="n">where</span> <span class="bp">|</span> <span class="n">zero</span> <span class="o">:</span> <span class="n">Nat</span> <span class="bp">|</span> <span class="n">succ</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">Nat</span><span class="o">)</span> <span class="o">:</span> <span class="n">Nat</span> </pre></div> </div> <p>You can find this in the library by writing <code class="docutils literal notranslate"><span class="pre">#check</span> <span class="pre">Nat</span></code> and
-
@@ -427,11 +423,11 @@ representations, but we don’t have to worry about the details of that now.<p>What “freely” means for the working mathematician is that the type <code class="docutils literal notranslate"><span class="pre">Nat</span></code> has an element <code class="docutils literal notranslate"><span class="pre">zero</span></code> and an injective successor function <code class="docutils literal notranslate"><span class="pre">succ</span></code> whose image does not include <code class="docutils literal notranslate"><span class="pre">zero</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">n.succ</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="n">Nat.zero</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Nat.succ_ne_zero</span><span class="w"> </span><span class="n">n</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">Nat</span><span class="o">)</span> <span class="o">:</span> <span class="n">n.succ</span> <span class="bp">≠</span> <span class="n">Nat.zero</span> <span class="o">:=</span> <span class="n">Nat.succ_ne_zero</span> <span class="n">n</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m.succ</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">n.succ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Nat.succ.inj</span><span class="w"> </span><span class="n">h</span> <span class="kd">example</span> <span class="o">(</span><span class="n">m</span> <span class="n">n</span> <span class="o">:</span> <span class="n">Nat</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">m.succ</span> <span class="bp">=</span> <span class="n">n.succ</span><span class="o">)</span> <span class="o">:</span> <span class="n">m</span> <span class="bp">=</span> <span class="n">n</span> <span class="o">:=</span> <span class="n">Nat.succ.inj</span> <span class="n">h</span> </pre></div> </div> <p>What the word “inductively” means for the working mathematician is that
-
@@ -440,9 +436,9 @@ and a principle of definition by recursion.This section will show you how to use these.</p> <p>Here is an example of a recursive definition of the factorial function.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">fac</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℕ</span> <span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">=></span><span class="w"> </span><span class="mi">1</span> <span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">=></span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">fac</span><span class="w"> </span><span class="n">n</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">fac</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">ℕ</span> <span class="bp">|</span> <span class="mi">0</span> <span class="bp">=></span> <span class="mi">1</span> <span class="bp">|</span> <span class="n">n</span> <span class="bp">+</span> <span class="mi">1</span> <span class="bp">=></span> <span class="o">(</span><span class="n">n</span> <span class="bp">+</span> <span class="mi">1</span><span class="o">)</span> <span class="bp">*</span> <span class="n">fac</span> <span class="n">n</span> </pre></div> </div> <p>The syntax takes some getting used to.
-
@@ -451,23 +447,23 @@ The next two lines provide the base case and inductive stepfor a recursive definition. These equations hold definitionally, but they can also be used manually by giving the name <code class="docutils literal notranslate"><span class="pre">fac</span></code> to <code class="docutils literal notranslate"><span class="pre">simp</span></code> or <code class="docutils literal notranslate"><span class="pre">rw</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">fac</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">fac</span> <span class="mi">0</span> <span class="bp">=</span> <span class="mi">1</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">fac</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">fac</span><span class="o">]</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">fac</span> <span class="mi">0</span> <span class="bp">=</span> <span class="mi">1</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">fac</span><span class="o">]</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">fac</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="o">[</span><span class="n">fac</span><span class="o">]</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">fac</span> <span class="mi">0</span> <span class="bp">=</span> <span class="mi">1</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> <span class="o">[</span><span class="n">fac</span><span class="o">]</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">fac</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">fac</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">example</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">:</span> <span class="n">fac</span> <span class="o">(</span><span class="n">n</span> <span class="bp">+</span> <span class="mi">1</span><span class="o">)</span> <span class="bp">=</span> <span class="o">(</span><span class="n">n</span> <span class="bp">+</span> <span class="mi">1</span><span class="o">)</span> <span class="bp">*</span> <span class="n">fac</span> <span class="n">n</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">fac</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">fac</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">fac</span><span class="o">]</span> <span class="kd">example</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">:</span> <span class="n">fac</span> <span class="o">(</span><span class="n">n</span> <span class="bp">+</span> <span class="mi">1</span><span class="o">)</span> <span class="bp">=</span> <span class="o">(</span><span class="n">n</span> <span class="bp">+</span> <span class="mi">1</span><span class="o">)</span> <span class="bp">*</span> <span class="n">fac</span> <span class="n">n</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">fac</span><span class="o">]</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">fac</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">fac</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="o">[</span><span class="n">fac</span><span class="o">]</span> <span class="kd">example</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">:</span> <span class="n">fac</span> <span class="o">(</span><span class="n">n</span> <span class="bp">+</span> <span class="mi">1</span><span class="o">)</span> <span class="bp">=</span> <span class="o">(</span><span class="n">n</span> <span class="bp">+</span> <span class="mi">1</span><span class="o">)</span> <span class="bp">*</span> <span class="n">fac</span> <span class="n">n</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> <span class="o">[</span><span class="n">fac</span><span class="o">]</span> </pre></div> </div> <p>The factorial function is actually already defined in Mathlib as
-
@@ -490,26 +486,26 @@ and a required to prove <code class="docutils literal notranslate"><span class="The phrase <code class="docutils literal notranslate"><span class="pre">with</span> <span class="pre">n</span> <span class="pre">ih</span></code> serves to name the variable and the assumption for the inductive hypothesis, and you can choose whatever names you want for them.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">fac_pos</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">fac</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">induction'</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">ih</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">fac</span><span class="o">]</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">zero_lt_one</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">fac</span><span class="o">]</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">mul_pos</span><span class="w"> </span><span class="n">n.succ_pos</span><span class="w"> </span><span class="n">ih</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">fac_pos</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp"><</span> <span class="n">fac</span> <span class="n">n</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">induction'</span> <span class="n">n</span> <span class="k">with</span> <span class="n">n</span> <span class="n">ih</span> <span class="bp">·</span> <span class="n">rw</span> <span class="o">[</span><span class="n">fac</span><span class="o">]</span> <span class="n">exact</span> <span class="n">zero_lt_one</span> <span class="n">rw</span> <span class="o">[</span><span class="n">fac</span><span class="o">]</span> <span class="n">exact</span> <span class="n">mul_pos</span> <span class="n">n.succ_pos</span> <span class="n">ih</span> </pre></div> </div> <p>The <code class="docutils literal notranslate"><span class="pre">induction</span></code> tactic is smart enough to include hypotheses that depend on the induction variable as part of the induction hypothesis. Step through the next example to see what is going on.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">dvd_fac</span><span class="w"> </span><span class="o">{</span><span class="n">i</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">ipos</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">ile</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">fac</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">induction'</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">ih</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">absurd</span><span class="w"> </span><span class="n">ipos</span><span class="w"> </span><span class="o">(</span><span class="n">not_lt_of_ge</span><span class="w"> </span><span class="n">ile</span><span class="o">)</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">fac</span><span class="o">]</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">Nat.of_le_succ</span><span class="w"> </span><span class="n">ile</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">dvd_mul_of_dvd_right</span><span class="w"> </span><span class="o">(</span><span class="n">ih</span><span class="w"> </span><span class="n">h</span><span class="o">)</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">h</span><span class="o">]</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">dvd_mul_right</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">dvd_fac</span> <span class="o">{</span><span class="n">i</span> <span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">}</span> <span class="o">(</span><span class="n">ipos</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp"><</span> <span class="n">i</span><span class="o">)</span> <span class="o">(</span><span class="n">ile</span> <span class="o">:</span> <span class="n">i</span> <span class="bp">≤</span> <span class="n">n</span><span class="o">)</span> <span class="o">:</span> <span class="n">i</span> <span class="bp">∣</span> <span class="n">fac</span> <span class="n">n</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">induction'</span> <span class="n">n</span> <span class="k">with</span> <span class="n">n</span> <span class="n">ih</span> <span class="bp">·</span> <span class="n">exact</span> <span class="n">absurd</span> <span class="n">ipos</span> <span class="o">(</span><span class="n">not_lt_of_ge</span> <span class="n">ile</span><span class="o">)</span> <span class="n">rw</span> <span class="o">[</span><span class="n">fac</span><span class="o">]</span> <span class="n">rcases</span> <span class="n">Nat.of_le_succ</span> <span class="n">ile</span> <span class="k">with</span> <span class="n">h</span> <span class="bp">|</span> <span class="n">h</span> <span class="bp">·</span> <span class="n">apply</span> <span class="n">dvd_mul_of_dvd_right</span> <span class="o">(</span><span class="n">ih</span> <span class="n">h</span><span class="o">)</span> <span class="n">rw</span> <span class="o">[</span><span class="n">h</span><span class="o">]</span> <span class="n">apply</span> <span class="n">dvd_mul_right</span> </pre></div> </div> <p>The following example provides a crude lower bound for the factorial
-
@@ -519,10 +515,10 @@ so that the remainder of the proof starts with the case<span class="math notranslate nohighlight">\(n = 1\)</span>. See if you can complete the argument with a proof by induction using <code class="docutils literal notranslate"><span class="pre">pow_succ</span></code> or <code class="docutils literal notranslate"><span class="pre">pow_succ'</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">pow_two_le_fac</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">fac</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">n</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="o">[</span><span class="n">fac</span><span class="o">]</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">pow_two_le_fac</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">:</span> <span class="mi">2</span> <span class="bp">^</span> <span class="o">(</span><span class="n">n</span> <span class="bp">-</span> <span class="mi">1</span><span class="o">)</span> <span class="bp">≤</span> <span class="n">fac</span> <span class="n">n</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rcases</span> <span class="n">n</span> <span class="k">with</span> <span class="n">_</span> <span class="bp">|</span> <span class="n">n</span> <span class="bp">·</span> <span class="n">simp</span> <span class="o">[</span><span class="n">fac</span><span class="o">]</span> <span class="gr">sorry</span> </pre></div> </div> <p>Induction is often used to prove identities involving finite sums and
-
@@ -541,50 +537,50 @@ it supports in the next section, and again in a later chapter.For now, we will only make use of <code class="docutils literal notranslate"><span class="pre">Finset.range</span> <span class="pre">n</span></code>, which is the finite set of natural numbers less than <code class="docutils literal notranslate"><span class="pre">n</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Finset</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">(</span><span class="n">s</span> <span class="o">:</span> <span class="n">Finset</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="n">Finset.sum</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="n">f</span> <span class="k">#check</span><span class="w"> </span><span class="n">Finset.prod</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="n">f</span> <span class="k">#check</span> <span class="n">Finset.sum</span> <span class="n">s</span> <span class="n">f</span> <span class="k">#check</span> <span class="n">Finset.prod</span> <span class="n">s</span> <span class="n">f</span> <span class="kn">open</span><span class="w"> </span><span class="n">BigOperators</span> <span class="kn">open</span><span class="w"> </span><span class="n">Finset</span> <span class="kn">open</span> <span class="n">BigOperators</span> <span class="kn">open</span> <span class="n">Finset</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s.sum</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">∑</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">s.sum</span> <span class="n">f</span> <span class="bp">=</span> <span class="bp">∑</span> <span class="n">x</span> <span class="k">in</span> <span class="n">s</span><span class="o">,</span> <span class="n">f</span> <span class="n">x</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s.prod</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">∏</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">s.prod</span> <span class="n">f</span> <span class="bp">=</span> <span class="bp">∏</span> <span class="n">x</span> <span class="k">in</span> <span class="n">s</span><span class="o">,</span> <span class="n">f</span> <span class="n">x</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">range</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="bp">.</span><span class="n">sum</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">∑</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">range</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">example</span> <span class="o">:</span> <span class="o">(</span><span class="n">range</span> <span class="n">n</span><span class="o">)</span><span class="bp">.</span><span class="n">sum</span> <span class="n">f</span> <span class="bp">=</span> <span class="bp">∑</span> <span class="n">x</span> <span class="k">in</span> <span class="n">range</span> <span class="n">n</span><span class="o">,</span> <span class="n">f</span> <span class="n">x</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">range</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="bp">.</span><span class="n">prod</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">∏</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">range</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">example</span> <span class="o">:</span> <span class="o">(</span><span class="n">range</span> <span class="n">n</span><span class="o">)</span><span class="bp">.</span><span class="n">prod</span> <span class="n">f</span> <span class="bp">=</span> <span class="bp">∏</span> <span class="n">x</span> <span class="k">in</span> <span class="n">range</span> <span class="n">n</span><span class="o">,</span> <span class="n">f</span> <span class="n">x</span> <span class="o">:=</span> <span class="n">rfl</span> </pre></div> </div> <p>The facts <code class="docutils literal notranslate"><span class="pre">Finset.sum_range_zero</span></code> and <code class="docutils literal notranslate"><span class="pre">Finset.sum_range_succ</span></code> provide a recursive description of summation up to <span class="math notranslate nohighlight">\(n\)</span>, and similarly for products.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∑</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">range</span><span class="w"> </span><span class="mi">0</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Finset.sum_range_zero</span><span class="w"> </span><span class="n">f</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∑</span> <span class="n">x</span> <span class="k">in</span> <span class="n">range</span> <span class="mi">0</span><span class="o">,</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">=</span> <span class="mi">0</span> <span class="o">:=</span> <span class="n">Finset.sum_range_zero</span> <span class="n">f</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∑</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">range</span><span class="w"> </span><span class="n">n.succ</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">∑</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">range</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Finset.sum_range_succ</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">n</span> <span class="kd">example</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∑</span> <span class="n">x</span> <span class="k">in</span> <span class="n">range</span> <span class="n">n.succ</span><span class="o">,</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">=</span> <span class="bp">∑</span> <span class="n">x</span> <span class="k">in</span> <span class="n">range</span> <span class="n">n</span><span class="o">,</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">f</span> <span class="n">n</span> <span class="o">:=</span> <span class="n">Finset.sum_range_succ</span> <span class="n">f</span> <span class="n">n</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∏</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">range</span><span class="w"> </span><span class="mi">0</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Finset.prod_range_zero</span><span class="w"> </span><span class="n">f</span> <span class="kd">example</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∏</span> <span class="n">x</span> <span class="k">in</span> <span class="n">range</span> <span class="mi">0</span><span class="o">,</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">=</span> <span class="mi">1</span> <span class="o">:=</span> <span class="n">Finset.prod_range_zero</span> <span class="n">f</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∏</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">range</span><span class="w"> </span><span class="n">n.succ</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">(</span><span class="bp">∏</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">range</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Finset.prod_range_succ</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">n</span> <span class="kd">example</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∏</span> <span class="n">x</span> <span class="k">in</span> <span class="n">range</span> <span class="n">n.succ</span><span class="o">,</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">=</span> <span class="o">(</span><span class="bp">∏</span> <span class="n">x</span> <span class="k">in</span> <span class="n">range</span> <span class="n">n</span><span class="o">,</span> <span class="n">f</span> <span class="n">x</span><span class="o">)</span> <span class="bp">*</span> <span class="n">f</span> <span class="n">n</span> <span class="o">:=</span> <span class="n">Finset.prod_range_succ</span> <span class="n">f</span> <span class="n">n</span> </pre></div> </div> <p>The first identity in each pair holds definitionally, which is to say, you can replace the proofs by <code class="docutils literal notranslate"><span class="pre">rfl</span></code>.</p> <p>The following expresses the factorial function that we defined as a product.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">fac</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">∏</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">range</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="o">(</span><span class="n">i</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">induction'</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">ih</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="o">[</span><span class="n">fac</span><span class="o">,</span><span class="w"> </span><span class="n">prod_range_zero</span><span class="o">]</span> <span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="o">[</span><span class="n">fac</span><span class="o">,</span><span class="w"> </span><span class="n">ih</span><span class="o">,</span><span class="w"> </span><span class="n">prod_range_succ</span><span class="o">,</span><span class="w"> </span><span class="n">mul_comm</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">:</span> <span class="n">fac</span> <span class="n">n</span> <span class="bp">=</span> <span class="bp">∏</span> <span class="n">i</span> <span class="k">in</span> <span class="n">range</span> <span class="n">n</span><span class="o">,</span> <span class="o">(</span><span class="n">i</span> <span class="bp">+</span> <span class="mi">1</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">induction'</span> <span class="n">n</span> <span class="k">with</span> <span class="n">n</span> <span class="n">ih</span> <span class="bp">·</span> <span class="n">simp</span> <span class="o">[</span><span class="n">fac</span><span class="o">,</span> <span class="n">prod_range_zero</span><span class="o">]</span> <span class="n">simp</span> <span class="o">[</span><span class="n">fac</span><span class="o">,</span> <span class="n">ih</span><span class="o">,</span> <span class="n">prod_range_succ</span><span class="o">,</span> <span class="n">mul_comm</span><span class="o">]</span> </pre></div> </div> <p>The fact that we include <code class="docutils literal notranslate"><span class="pre">mul_comm</span></code> as a simplification rule deserves
-
@@ -598,8 +594,8 @@ The following example shows that simplifying using the three rules<code class="docutils literal notranslate"><span class="pre">mul_assoc</span></code>, <code class="docutils literal notranslate"><span class="pre">mul_comm</span></code>, and <code class="docutils literal notranslate"><span class="pre">mul_left_comm</span></code> manages to identify products that are the same up to the placement of parentheses and ordering of variables.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="n">e</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">d</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">e</span><span class="o">))</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">e</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">c</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="o">[</span><span class="n">mul_assoc</span><span class="o">,</span><span class="w"> </span><span class="n">mul_comm</span><span class="o">,</span><span class="w"> </span><span class="n">mul_left_comm</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="n">d</span> <span class="n">e</span> <span class="n">f</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">*</span> <span class="o">(</span><span class="n">b</span> <span class="bp">*</span> <span class="n">c</span> <span class="bp">*</span> <span class="n">f</span> <span class="bp">*</span> <span class="o">(</span><span class="n">d</span> <span class="bp">*</span> <span class="n">e</span><span class="o">))</span> <span class="bp">=</span> <span class="n">d</span> <span class="bp">*</span> <span class="o">(</span><span class="n">a</span> <span class="bp">*</span> <span class="n">f</span> <span class="bp">*</span> <span class="n">e</span><span class="o">)</span> <span class="bp">*</span> <span class="o">(</span><span class="n">c</span> <span class="bp">*</span> <span class="n">b</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> <span class="o">[</span><span class="n">mul_assoc</span><span class="o">,</span> <span class="n">mul_comm</span><span class="o">,</span> <span class="n">mul_left_comm</span><span class="o">]</span> </pre></div> </div> <p>Roughly, the rules work by pushing parentheses to the right
-
@@ -613,18 +609,18 @@ The first step of the proof clears the denominator.This is generally useful when formalizing identities, because calculations with division generally have side conditions. (It is similarly useful to avoid using subtraction on the natural numbers when possible.)</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">sum_id</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∑</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">range</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="o">),</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">symm</span><span class="bp">;</span><span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">Nat.div_eq_of_eq_mul_right</span><span class="w"> </span><span class="o">(</span><span class="kd">by</span><span class="w"> </span><span class="n">norm_num</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="mi">2</span><span class="o">)</span> <span class="w"> </span><span class="n">induction'</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">ih</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">simp</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">Finset.sum_range_succ</span><span class="o">,</span><span class="w"> </span><span class="n">mul_add</span><span class="w"> </span><span class="mi">2</span><span class="o">,</span><span class="w"> </span><span class="bp">←</span><span class="w"> </span><span class="n">ih</span><span class="o">]</span> <span class="w"> </span><span class="n">ring</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">sum_id</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∑</span> <span class="n">i</span> <span class="k">in</span> <span class="n">range</span> <span class="o">(</span><span class="n">n</span> <span class="bp">+</span> <span class="mi">1</span><span class="o">),</span> <span class="n">i</span> <span class="bp">=</span> <span class="n">n</span> <span class="bp">*</span> <span class="o">(</span><span class="n">n</span> <span class="bp">+</span> <span class="mi">1</span><span class="o">)</span> <span class="bp">/</span> <span class="mi">2</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">symm</span><span class="bp">;</span> <span class="n">apply</span> <span class="n">Nat.div_eq_of_eq_mul_right</span> <span class="o">(</span><span class="kd">by</span> <span class="n">norm_num</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp"><</span> <span class="mi">2</span><span class="o">)</span> <span class="n">induction'</span> <span class="n">n</span> <span class="k">with</span> <span class="n">n</span> <span class="n">ih</span> <span class="bp">·</span> <span class="n">simp</span> <span class="n">rw</span> <span class="o">[</span><span class="n">Finset.sum_range_succ</span><span class="o">,</span> <span class="n">mul_add</span> <span class="mi">2</span><span class="o">,</span> <span class="bp">←</span> <span class="n">ih</span><span class="o">]</span> <span class="n">ring</span> </pre></div> </div> <p>We encourage you to prove the analogous identity for sums of squares, and other identities you can find on the web.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">sum_sqr</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∑</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">range</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="o">),</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="mi">2</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">6</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">sum_sqr</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∑</span> <span class="n">i</span> <span class="k">in</span> <span class="n">range</span> <span class="o">(</span><span class="n">n</span> <span class="bp">+</span> <span class="mi">1</span><span class="o">),</span> <span class="n">i</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">=</span> <span class="n">n</span> <span class="bp">*</span> <span class="o">(</span><span class="n">n</span> <span class="bp">+</span> <span class="mi">1</span><span class="o">)</span> <span class="bp">*</span> <span class="o">(</span><span class="mi">2</span> <span class="bp">*</span> <span class="n">n</span> <span class="bp">+</span> <span class="mi">1</span><span class="o">)</span> <span class="bp">/</span> <span class="mi">6</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>In Lean’s core library, addition and multiplication are themselves defined
-
@@ -663,53 +659,53 @@ Remember that truncated subtraction cuts off at zero.To define that, it is useful to define a predecessor function, <code class="docutils literal notranslate"><span class="pre">pred</span></code>, that subtracts one from any nonzero number and fixes zero. The function <code class="docutils literal notranslate"><span class="pre">pred</span></code> can be defined by a simple instance of recursion.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">inductive</span><span class="w"> </span><span class="n">MyNat</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">zero</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">MyNat</span> <span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">succ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">MyNat</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">MyNat</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">inductive</span> <span class="n">MyNat</span> <span class="n">where</span> <span class="bp">|</span> <span class="n">zero</span> <span class="o">:</span> <span class="n">MyNat</span> <span class="bp">|</span> <span class="n">succ</span> <span class="o">:</span> <span class="n">MyNat</span> <span class="bp">→</span> <span class="n">MyNat</span> <span class="kn">namespace</span><span class="w"> </span><span class="n">MyNat</span> <span class="kn">namespace</span> <span class="n">MyNat</span> <span class="kd">def</span><span class="w"> </span><span class="n">add</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">MyNat</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">MyNat</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">MyNat</span> <span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">zero</span><span class="w"> </span><span class="bp">=></span><span class="w"> </span><span class="n">x</span> <span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">succ</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">=></span><span class="w"> </span><span class="n">succ</span><span class="w"> </span><span class="o">(</span><span class="n">add</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="o">)</span> <span class="kd">def</span> <span class="n">add</span> <span class="o">:</span> <span class="n">MyNat</span> <span class="bp">→</span> <span class="n">MyNat</span> <span class="bp">→</span> <span class="n">MyNat</span> <span class="bp">|</span> <span class="n">x</span><span class="o">,</span> <span class="n">zero</span> <span class="bp">=></span> <span class="n">x</span> <span class="bp">|</span> <span class="n">x</span><span class="o">,</span> <span class="n">succ</span> <span class="n">y</span> <span class="bp">=></span> <span class="n">succ</span> <span class="o">(</span><span class="n">add</span> <span class="n">x</span> <span class="n">y</span><span class="o">)</span> <span class="kd">def</span><span class="w"> </span><span class="n">mul</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">MyNat</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">MyNat</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">MyNat</span> <span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">zero</span><span class="w"> </span><span class="bp">=></span><span class="w"> </span><span class="n">zero</span> <span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">succ</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">=></span><span class="w"> </span><span class="n">add</span><span class="w"> </span><span class="o">(</span><span class="n">mul</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="n">x</span> <span class="kd">def</span> <span class="n">mul</span> <span class="o">:</span> <span class="n">MyNat</span> <span class="bp">→</span> <span class="n">MyNat</span> <span class="bp">→</span> <span class="n">MyNat</span> <span class="bp">|</span> <span class="n">x</span><span class="o">,</span> <span class="n">zero</span> <span class="bp">=></span> <span class="n">zero</span> <span class="bp">|</span> <span class="n">x</span><span class="o">,</span> <span class="n">succ</span> <span class="n">y</span> <span class="bp">=></span> <span class="n">add</span> <span class="o">(</span><span class="n">mul</span> <span class="n">x</span> <span class="n">y</span><span class="o">)</span> <span class="n">x</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">zero_add</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">MyNat</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">add</span><span class="w"> </span><span class="n">zero</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">induction'</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">ih</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">rfl</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">add</span><span class="o">,</span><span class="w"> </span><span class="n">ih</span><span class="o">]</span> <span class="kd">theorem</span> <span class="n">zero_add</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">MyNat</span><span class="o">)</span> <span class="o">:</span> <span class="n">add</span> <span class="n">zero</span> <span class="n">n</span> <span class="bp">=</span> <span class="n">n</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">induction'</span> <span class="n">n</span> <span class="k">with</span> <span class="n">n</span> <span class="n">ih</span> <span class="bp">·</span> <span class="n">rfl</span> <span class="n">rw</span> <span class="o">[</span><span class="n">add</span><span class="o">,</span> <span class="n">ih</span><span class="o">]</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">succ_add</span><span class="w"> </span><span class="o">(</span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">MyNat</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">add</span><span class="w"> </span><span class="o">(</span><span class="n">succ</span><span class="w"> </span><span class="n">m</span><span class="o">)</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">succ</span><span class="w"> </span><span class="o">(</span><span class="n">add</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">induction'</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">ih</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">rfl</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">add</span><span class="o">,</span><span class="w"> </span><span class="n">ih</span><span class="o">]</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">theorem</span> <span class="n">succ_add</span> <span class="o">(</span><span class="n">m</span> <span class="n">n</span> <span class="o">:</span> <span class="n">MyNat</span><span class="o">)</span> <span class="o">:</span> <span class="n">add</span> <span class="o">(</span><span class="n">succ</span> <span class="n">m</span><span class="o">)</span> <span class="n">n</span> <span class="bp">=</span> <span class="n">succ</span> <span class="o">(</span><span class="n">add</span> <span class="n">m</span> <span class="n">n</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">induction'</span> <span class="n">n</span> <span class="k">with</span> <span class="n">n</span> <span class="n">ih</span> <span class="bp">·</span> <span class="n">rfl</span> <span class="n">rw</span> <span class="o">[</span><span class="n">add</span><span class="o">,</span> <span class="n">ih</span><span class="o">]</span> <span class="n">rfl</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">add_comm</span><span class="w"> </span><span class="o">(</span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">MyNat</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">add</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">add</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">induction'</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">ih</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">zero_add</span><span class="o">]</span> <span class="w"> </span><span class="n">rfl</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">add</span><span class="o">,</span><span class="w"> </span><span class="n">succ_add</span><span class="o">,</span><span class="w"> </span><span class="n">ih</span><span class="o">]</span> <span class="kd">theorem</span> <span class="n">add_comm</span> <span class="o">(</span><span class="n">m</span> <span class="n">n</span> <span class="o">:</span> <span class="n">MyNat</span><span class="o">)</span> <span class="o">:</span> <span class="n">add</span> <span class="n">m</span> <span class="n">n</span> <span class="bp">=</span> <span class="n">add</span> <span class="n">n</span> <span class="n">m</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">induction'</span> <span class="n">n</span> <span class="k">with</span> <span class="n">n</span> <span class="n">ih</span> <span class="bp">·</span> <span class="n">rw</span> <span class="o">[</span><span class="n">zero_add</span><span class="o">]</span> <span class="n">rfl</span> <span class="n">rw</span> <span class="o">[</span><span class="n">add</span><span class="o">,</span> <span class="n">succ_add</span><span class="o">,</span> <span class="n">ih</span><span class="o">]</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">add_assoc</span><span class="w"> </span><span class="o">(</span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">k</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">MyNat</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">add</span><span class="w"> </span><span class="o">(</span><span class="n">add</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="n">k</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">add</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="o">(</span><span class="n">add</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">k</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">mul_add</span><span class="w"> </span><span class="o">(</span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">k</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">MyNat</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">mul</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="o">(</span><span class="n">add</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">k</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">add</span><span class="w"> </span><span class="o">(</span><span class="n">mul</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">mul</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="n">k</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">zero_mul</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">MyNat</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">mul</span><span class="w"> </span><span class="n">zero</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">zero</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">succ_mul</span><span class="w"> </span><span class="o">(</span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">MyNat</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">mul</span><span class="w"> </span><span class="o">(</span><span class="n">succ</span><span class="w"> </span><span class="n">m</span><span class="o">)</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">add</span><span class="w"> </span><span class="o">(</span><span class="n">mul</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">mul_comm</span><span class="w"> </span><span class="o">(</span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">MyNat</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">mul</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">mul</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">end</span><span class="w"> </span><span class="n">MyNat</span> <span class="kd">theorem</span> <span class="n">add_assoc</span> <span class="o">(</span><span class="n">m</span> <span class="n">n</span> <span class="n">k</span> <span class="o">:</span> <span class="n">MyNat</span><span class="o">)</span> <span class="o">:</span> <span class="n">add</span> <span class="o">(</span><span class="n">add</span> <span class="n">m</span> <span class="n">n</span><span class="o">)</span> <span class="n">k</span> <span class="bp">=</span> <span class="n">add</span> <span class="n">m</span> <span class="o">(</span><span class="n">add</span> <span class="n">n</span> <span class="n">k</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">theorem</span> <span class="n">mul_add</span> <span class="o">(</span><span class="n">m</span> <span class="n">n</span> <span class="n">k</span> <span class="o">:</span> <span class="n">MyNat</span><span class="o">)</span> <span class="o">:</span> <span class="n">mul</span> <span class="n">m</span> <span class="o">(</span><span class="n">add</span> <span class="n">n</span> <span class="n">k</span><span class="o">)</span> <span class="bp">=</span> <span class="n">add</span> <span class="o">(</span><span class="n">mul</span> <span class="n">m</span> <span class="n">n</span><span class="o">)</span> <span class="o">(</span><span class="n">mul</span> <span class="n">m</span> <span class="n">k</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">theorem</span> <span class="n">zero_mul</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">MyNat</span><span class="o">)</span> <span class="o">:</span> <span class="n">mul</span> <span class="n">zero</span> <span class="n">n</span> <span class="bp">=</span> <span class="n">zero</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">theorem</span> <span class="n">succ_mul</span> <span class="o">(</span><span class="n">m</span> <span class="n">n</span> <span class="o">:</span> <span class="n">MyNat</span><span class="o">)</span> <span class="o">:</span> <span class="n">mul</span> <span class="o">(</span><span class="n">succ</span> <span class="n">m</span><span class="o">)</span> <span class="n">n</span> <span class="bp">=</span> <span class="n">add</span> <span class="o">(</span><span class="n">mul</span> <span class="n">m</span> <span class="n">n</span><span class="o">)</span> <span class="n">n</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">theorem</span> <span class="n">mul_comm</span> <span class="o">(</span><span class="n">m</span> <span class="n">n</span> <span class="o">:</span> <span class="n">MyNat</span><span class="o">)</span> <span class="o">:</span> <span class="n">mul</span> <span class="n">m</span> <span class="n">n</span> <span class="bp">=</span> <span class="n">mul</span> <span class="n">n</span> <span class="n">m</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">end</span> <span class="n">MyNat</span> </pre></div> </div> </section> <section id="infinitely-many-primes"> <span id="section-infinitely-many-primes"></span><h2><span class="section-number">5.3. </span>Infinitely Many Primes<a class="headerlink" href="#infinitely-many-primes" title="Link to this heading"></a></h2> <span id="section-infinitely-many-primes"></span><h2><span class="section-number">5.3. </span>Infinitely Many Primes<a class="headerlink" href="#infinitely-many-primes" title="Permalink to this heading"></a></h2> <p>Let us continue our exploration of induction and recursion with another mathematical standard: a proof that there are infinitely many primes. One way to formulate this is as the statement that
-
@@ -729,12 +725,12 @@ annoying to formalize.Here we consider a few ways to do it.</p> <p>To start with, we can use the <code class="docutils literal notranslate"><span class="pre">cases</span></code> tactic and the fact that the successor function respects the ordering on the natural numbers.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">two_le</span><span class="w"> </span><span class="o">{</span><span class="n">m</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h0</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">cases</span><span class="w"> </span><span class="n">m</span><span class="bp">;</span><span class="w"> </span><span class="n">contradiction</span> <span class="w"> </span><span class="n">case</span><span class="w"> </span><span class="n">succ</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">=></span> <span class="w"> </span><span class="n">cases</span><span class="w"> </span><span class="n">m</span><span class="bp">;</span><span class="w"> </span><span class="n">contradiction</span> <span class="w"> </span><span class="n">repeat</span><span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">Nat.succ_le_succ</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">zero_le</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">two_le</span> <span class="o">{</span><span class="n">m</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">}</span> <span class="o">(</span><span class="n">h0</span> <span class="o">:</span> <span class="n">m</span> <span class="bp">≠</span> <span class="mi">0</span><span class="o">)</span> <span class="o">(</span><span class="n">h1</span> <span class="o">:</span> <span class="n">m</span> <span class="bp">≠</span> <span class="mi">1</span><span class="o">)</span> <span class="o">:</span> <span class="mi">2</span> <span class="bp">≤</span> <span class="n">m</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">cases</span> <span class="n">m</span><span class="bp">;</span> <span class="n">contradiction</span> <span class="n">case</span> <span class="n">succ</span> <span class="n">m</span> <span class="bp">=></span> <span class="n">cases</span> <span class="n">m</span><span class="bp">;</span> <span class="n">contradiction</span> <span class="n">repeat</span> <span class="n">apply</span> <span class="n">Nat.succ_le_succ</span> <span class="n">apply</span> <span class="n">zero_le</span> </pre></div> </div> <p>Another strategy is to use the tactic <code class="docutils literal notranslate"><span class="pre">interval_cases</span></code>,
-
@@ -742,10 +738,10 @@ which automatically splits the goal into cases whenthe variable in question is contained in an interval of natural numbers or integers. Remember that you can hover over it to see its documentation.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">m</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h0</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">by_contra</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="n">push_neg</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="n">interval_cases</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">contradiction</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">m</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">}</span> <span class="o">(</span><span class="n">h0</span> <span class="o">:</span> <span class="n">m</span> <span class="bp">≠</span> <span class="mi">0</span><span class="o">)</span> <span class="o">(</span><span class="n">h1</span> <span class="o">:</span> <span class="n">m</span> <span class="bp">≠</span> <span class="mi">1</span><span class="o">)</span> <span class="o">:</span> <span class="mi">2</span> <span class="bp">≤</span> <span class="n">m</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">by_contra</span> <span class="n">h</span> <span class="n">push_neg</span> <span class="n">at</span> <span class="n">h</span> <span class="n">interval_cases</span> <span class="n">m</span> <span class="bp"><;></span> <span class="n">contradiction</span> </pre></div> </div> <p id="index-0">Recall that the semicolon after <code class="docutils literal notranslate"><span class="pre">interval_cases</span> <span class="pre">m</span></code> means
-
@@ -755,12 +751,12 @@ to find a decision procedure to solve the problem.Lean knows that you can decide the truth value of a statement that begins with a bounded quantifier <code class="docutils literal notranslate"><span class="pre">∀</span> <span class="pre">x,</span> <span class="pre">x</span> <span class="pre"><</span> <span class="pre">n</span> <span class="pre">→</span> <span class="pre">...</span></code> or <code class="docutils literal notranslate"><span class="pre">∃</span> <span class="pre">x,</span> <span class="pre">x</span> <span class="pre"><</span> <span class="pre">n</span> <span class="pre">∧</span> <span class="pre">...</span></code> by deciding each of the finitely many instances.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">m</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h0</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">by_contra</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="n">push_neg</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="n">revert</span><span class="w"> </span><span class="n">h0</span><span class="w"> </span><span class="n">h1</span> <span class="w"> </span><span class="n">revert</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="n">m</span> <span class="w"> </span><span class="n">decide</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">m</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">}</span> <span class="o">(</span><span class="n">h0</span> <span class="o">:</span> <span class="n">m</span> <span class="bp">≠</span> <span class="mi">0</span><span class="o">)</span> <span class="o">(</span><span class="n">h1</span> <span class="o">:</span> <span class="n">m</span> <span class="bp">≠</span> <span class="mi">1</span><span class="o">)</span> <span class="o">:</span> <span class="mi">2</span> <span class="bp">≤</span> <span class="n">m</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">by_contra</span> <span class="n">h</span> <span class="n">push_neg</span> <span class="n">at</span> <span class="n">h</span> <span class="n">revert</span> <span class="n">h0</span> <span class="n">h1</span> <span class="n">revert</span> <span class="n">h</span> <span class="n">m</span> <span class="n">decide</span> </pre></div> </div> <p>With the theorem <code class="docutils literal notranslate"><span class="pre">two_le</span></code> in hand, let’s start by showing that every
-
@@ -785,44 +781,44 @@ then by one of the characterizations of what it means to be a prime number,it has a nontrivial factor, <span class="math notranslate nohighlight">\(m\)</span>, and we can apply the inductive hypothesis to that. Step through the next proof to see how that plays out.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">exists_prime_factor</span><span class="w"> </span><span class="o">{</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat</span><span class="o">,</span><span class="w"> </span><span class="n">p.Prime</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">by_cases</span><span class="w"> </span><span class="n">np</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">n.Prime</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="n">np</span> <span class="w"> </span><span class="n">induction'</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">using</span><span class="w"> </span><span class="n">Nat.strong_induction_on</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">ih</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">Nat.prime_def_lt</span><span class="o">]</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">np</span> <span class="w"> </span><span class="n">push_neg</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">np</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">np</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">m</span><span class="o">,</span><span class="w"> </span><span class="n">mltn</span><span class="o">,</span><span class="w"> </span><span class="n">mdvdn</span><span class="o">,</span><span class="w"> </span><span class="n">mne1</span><span class="o">⟩</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">mz</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">mz</span><span class="o">,</span><span class="w"> </span><span class="n">zero_dvd_iff</span><span class="o">]</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">mdvdn</span> <span class="w"> </span><span class="n">linarith</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">mgt2</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">two_le</span><span class="w"> </span><span class="n">this</span><span class="w"> </span><span class="n">mne1</span> <span class="w"> </span><span class="n">by_cases</span><span class="w"> </span><span class="n">mp</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m.Prime</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">m</span><span class="o">,</span><span class="w"> </span><span class="n">mp</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">ih</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="n">mltn</span><span class="w"> </span><span class="n">mgt2</span><span class="w"> </span><span class="n">mp</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">p</span><span class="o">,</span><span class="w"> </span><span class="n">pp</span><span class="o">,</span><span class="w"> </span><span class="n">pdvd</span><span class="o">⟩</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">p</span><span class="o">,</span><span class="w"> </span><span class="n">pp</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">pdvd.trans</span><span class="w"> </span><span class="n">mdvdn</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">exists_prime_factor</span> <span class="o">{</span><span class="n">n</span> <span class="o">:</span> <span class="n">Nat</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="mi">2</span> <span class="bp">≤</span> <span class="n">n</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">p</span> <span class="o">:</span> <span class="n">Nat</span><span class="o">,</span> <span class="n">p.Prime</span> <span class="bp">∧</span> <span class="n">p</span> <span class="bp">∣</span> <span class="n">n</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">by_cases</span> <span class="n">np</span> <span class="o">:</span> <span class="n">n.Prime</span> <span class="bp">·</span> <span class="n">use</span> <span class="n">n</span><span class="o">,</span> <span class="n">np</span> <span class="n">induction'</span> <span class="n">n</span> <span class="n">using</span> <span class="n">Nat.strong_induction_on</span> <span class="k">with</span> <span class="n">n</span> <span class="n">ih</span> <span class="n">rw</span> <span class="o">[</span><span class="n">Nat.prime_def_lt</span><span class="o">]</span> <span class="n">at</span> <span class="n">np</span> <span class="n">push_neg</span> <span class="n">at</span> <span class="n">np</span> <span class="n">rcases</span> <span class="n">np</span> <span class="n">h</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">m</span><span class="o">,</span> <span class="n">mltn</span><span class="o">,</span> <span class="n">mdvdn</span><span class="o">,</span> <span class="n">mne1</span><span class="o">⟩</span> <span class="k">have</span> <span class="o">:</span> <span class="n">m</span> <span class="bp">≠</span> <span class="mi">0</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">mz</span> <span class="n">rw</span> <span class="o">[</span><span class="n">mz</span><span class="o">,</span> <span class="n">zero_dvd_iff</span><span class="o">]</span> <span class="n">at</span> <span class="n">mdvdn</span> <span class="n">linarith</span> <span class="k">have</span> <span class="n">mgt2</span> <span class="o">:</span> <span class="mi">2</span> <span class="bp">≤</span> <span class="n">m</span> <span class="o">:=</span> <span class="n">two_le</span> <span class="n">this</span> <span class="n">mne1</span> <span class="n">by_cases</span> <span class="n">mp</span> <span class="o">:</span> <span class="n">m.Prime</span> <span class="bp">·</span> <span class="n">use</span> <span class="n">m</span><span class="o">,</span> <span class="n">mp</span> <span class="bp">·</span> <span class="n">rcases</span> <span class="n">ih</span> <span class="n">m</span> <span class="n">mltn</span> <span class="n">mgt2</span> <span class="n">mp</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">p</span><span class="o">,</span> <span class="n">pp</span><span class="o">,</span> <span class="n">pdvd</span><span class="o">⟩</span> <span class="n">use</span> <span class="n">p</span><span class="o">,</span> <span class="n">pp</span> <span class="n">apply</span> <span class="n">pdvd.trans</span> <span class="n">mdvdn</span> </pre></div> </div> <p>We can now prove the following formulation of our theorem. See if you can fill out the sketch. You can use <code class="docutils literal notranslate"><span class="pre">Nat.factorial_pos</span></code>, <code class="docutils literal notranslate"><span class="pre">Nat.dvd_factorial</span></code>, and <code class="docutils literal notranslate"><span class="pre">Nat.dvd_sub'</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">primes_infinite</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="n">Nat.Prime</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">n</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">Nat.factorial</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">exists_prime_factor</span><span class="w"> </span><span class="n">this</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">p</span><span class="o">,</span><span class="w"> </span><span class="n">pp</span><span class="o">,</span><span class="w"> </span><span class="n">pdvd</span><span class="o">⟩</span> <span class="w"> </span><span class="n">refine</span><span class="w"> </span><span class="o">⟨</span><span class="n">p</span><span class="o">,</span><span class="w"> </span><span class="bp">?</span><span class="n">_</span><span class="o">,</span><span class="w"> </span><span class="n">pp</span><span class="o">⟩</span> <span class="w"> </span><span class="k">show</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="n">n</span> <span class="w"> </span><span class="n">by_contra</span><span class="w"> </span><span class="n">ple</span> <span class="w"> </span><span class="n">push_neg</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">ple</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">Nat.factorial</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="k">show</span><span class="w"> </span><span class="n">False</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">primes_infinite</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">n</span><span class="o">,</span> <span class="bp">∃</span> <span class="n">p</span> <span class="bp">></span> <span class="n">n</span><span class="o">,</span> <span class="n">Nat.Prime</span> <span class="n">p</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">n</span> <span class="k">have</span> <span class="o">:</span> <span class="mi">2</span> <span class="bp">≤</span> <span class="n">Nat.factorial</span> <span class="o">(</span><span class="n">n</span> <span class="bp">+</span> <span class="mi">1</span><span class="o">)</span> <span class="bp">+</span> <span class="mi">1</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="n">rcases</span> <span class="n">exists_prime_factor</span> <span class="n">this</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">p</span><span class="o">,</span> <span class="n">pp</span><span class="o">,</span> <span class="n">pdvd</span><span class="o">⟩</span> <span class="n">refine</span> <span class="o">⟨</span><span class="n">p</span><span class="o">,</span> <span class="bp">?</span><span class="n">_</span><span class="o">,</span> <span class="n">pp</span><span class="o">⟩</span> <span class="k">show</span> <span class="n">p</span> <span class="bp">></span> <span class="n">n</span> <span class="n">by_contra</span> <span class="n">ple</span> <span class="n">push_neg</span> <span class="n">at</span> <span class="n">ple</span> <span class="k">have</span> <span class="o">:</span> <span class="n">p</span> <span class="bp">∣</span> <span class="n">Nat.factorial</span> <span class="o">(</span><span class="n">n</span> <span class="bp">+</span> <span class="mi">1</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="k">have</span> <span class="o">:</span> <span class="n">p</span> <span class="bp">∣</span> <span class="mi">1</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="k">show</span> <span class="n">False</span> <span class="gr">sorry</span> </pre></div> </div> <p>Let’s consider a variation of the proof above, where instead
-
@@ -851,31 +847,31 @@ so they need to be expanded manually using equivalences likeand <code class="docutils literal notranslate"><span class="pre">Finset.mem_sdiff</span></code>. The <code class="docutils literal notranslate"><span class="pre">ext</span></code> tactic can still be used to show that two finite sets are equal by showing that every element of one is an element of the other.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span><span class="w"> </span><span class="n">Finset</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span> <span class="n">Finset</span> <span class="kn">section</span> <span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">DecidableEq</span><span class="w"> </span><span class="n">α</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">r</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Finset</span><span class="w"> </span><span class="n">α</span><span class="o">)</span> <span class="kd">variable</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">DecidableEq</span> <span class="n">α</span><span class="o">]</span> <span class="o">(</span><span class="n">r</span> <span class="n">s</span> <span class="n">t</span> <span class="o">:</span> <span class="n">Finset</span> <span class="n">α</span><span class="o">)</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">t</span><span class="o">)</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">subset_iff</span><span class="o">]</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">x</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">mem_inter</span><span class="o">,</span><span class="w"> </span><span class="n">mem_union</span><span class="o">,</span><span class="w"> </span><span class="n">mem_union</span><span class="o">,</span><span class="w"> </span><span class="n">mem_inter</span><span class="o">,</span><span class="w"> </span><span class="n">mem_inter</span><span class="o">]</span> <span class="w"> </span><span class="n">tauto</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">r</span> <span class="bp">∩</span> <span class="o">(</span><span class="n">s</span> <span class="bp">∪</span> <span class="n">t</span><span class="o">)</span> <span class="bp">⊆</span> <span class="n">r</span> <span class="bp">∩</span> <span class="n">s</span> <span class="bp">∪</span> <span class="n">r</span> <span class="bp">∩</span> <span class="n">t</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">subset_iff</span><span class="o">]</span> <span class="n">intro</span> <span class="n">x</span> <span class="n">rw</span> <span class="o">[</span><span class="n">mem_inter</span><span class="o">,</span> <span class="n">mem_union</span><span class="o">,</span> <span class="n">mem_union</span><span class="o">,</span> <span class="n">mem_inter</span><span class="o">,</span> <span class="n">mem_inter</span><span class="o">]</span> <span class="n">tauto</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">t</span><span class="o">)</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="o">[</span><span class="n">subset_iff</span><span class="o">]</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">x</span> <span class="w"> </span><span class="n">tauto</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">r</span> <span class="bp">∩</span> <span class="o">(</span><span class="n">s</span> <span class="bp">∪</span> <span class="n">t</span><span class="o">)</span> <span class="bp">⊆</span> <span class="n">r</span> <span class="bp">∩</span> <span class="n">s</span> <span class="bp">∪</span> <span class="n">r</span> <span class="bp">∩</span> <span class="n">t</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> <span class="o">[</span><span class="n">subset_iff</span><span class="o">]</span> <span class="n">intro</span> <span class="n">x</span> <span class="n">tauto</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">t</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="o">[</span><span class="n">subset_iff</span><span class="o">]</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">x</span> <span class="w"> </span><span class="n">tauto</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">r</span> <span class="bp">∩</span> <span class="n">s</span> <span class="bp">∪</span> <span class="n">r</span> <span class="bp">∩</span> <span class="n">t</span> <span class="bp">⊆</span> <span class="n">r</span> <span class="bp">∩</span> <span class="o">(</span><span class="n">s</span> <span class="bp">∪</span> <span class="n">t</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> <span class="o">[</span><span class="n">subset_iff</span><span class="o">]</span> <span class="n">intro</span> <span class="n">x</span> <span class="n">tauto</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">t</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">ext</span><span class="w"> </span><span class="n">x</span> <span class="w"> </span><span class="n">simp</span> <span class="w"> </span><span class="n">tauto</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">r</span> <span class="bp">∩</span> <span class="n">s</span> <span class="bp">∪</span> <span class="n">r</span> <span class="bp">∩</span> <span class="n">t</span> <span class="bp">=</span> <span class="n">r</span> <span class="bp">∩</span> <span class="o">(</span><span class="n">s</span> <span class="bp">∪</span> <span class="n">t</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">ext</span> <span class="n">x</span> <span class="n">simp</span> <span class="n">tauto</span> <span class="kd">end</span> </pre></div>
-
@@ -884,27 +880,27 @@ that every element of one is an element of the other.</p>version, <code class="docutils literal notranslate"><span class="pre">tauto!</span></code>, which uses classical logic) can be used to dispense with propositional tautologies. See if you can use these methods to prove the two examples below.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">r</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">s</span><span class="o">)</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="o">(</span><span class="n">r</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">t</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">r</span><span class="w"> </span><span class="bp">\</span><span class="w"> </span><span class="n">s</span><span class="o">)</span><span class="w"> </span><span class="bp">\</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="bp">\</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="n">t</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="o">(</span><span class="n">r</span> <span class="bp">∪</span> <span class="n">s</span><span class="o">)</span> <span class="bp">∩</span> <span class="o">(</span><span class="n">r</span> <span class="bp">∪</span> <span class="n">t</span><span class="o">)</span> <span class="bp">=</span> <span class="n">r</span> <span class="bp">∪</span> <span class="n">s</span> <span class="bp">∩</span> <span class="n">t</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span> <span class="o">:</span> <span class="o">(</span><span class="n">r</span> <span class="bp">\</span> <span class="n">s</span><span class="o">)</span> <span class="bp">\</span> <span class="n">t</span> <span class="bp">=</span> <span class="n">r</span> <span class="bp">\</span> <span class="o">(</span><span class="n">s</span> <span class="bp">∪</span> <span class="n">t</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>The theorem <code class="docutils literal notranslate"><span class="pre">Finset.dvd_prod_of_mem</span></code> tells us that if an <code class="docutils literal notranslate"><span class="pre">n</span></code> is an element of a finite set <code class="docutils literal notranslate"><span class="pre">s</span></code>, then <code class="docutils literal notranslate"><span class="pre">n</span></code> divides <code class="docutils literal notranslate"><span class="pre">∏</span> <span class="pre">i</span> <span class="pre">in</span> <span class="pre">s,</span> <span class="pre">i</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Finset</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="bp">∏</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Finset.dvd_prod_of_mem</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="n">h</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">s</span> <span class="o">:</span> <span class="n">Finset</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">n</span> <span class="bp">∈</span> <span class="n">s</span><span class="o">)</span> <span class="o">:</span> <span class="n">n</span> <span class="bp">∣</span> <span class="bp">∏</span> <span class="n">i</span> <span class="k">in</span> <span class="n">s</span><span class="o">,</span> <span class="n">i</span> <span class="o">:=</span> <span class="n">Finset.dvd_prod_of_mem</span> <span class="n">_</span> <span class="n">h</span> </pre></div> </div> <p>We also need to know that the converse holds in the case where <code class="docutils literal notranslate"><span class="pre">n</span></code> is prime and <code class="docutils literal notranslate"><span class="pre">s</span></code> is a set of primes. To show that, we need the following lemma, which you should be able to prove using the theorem <code class="docutils literal notranslate"><span class="pre">Nat.Prime.eq_one_or_self_of_dvd</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">_root_.Nat.Prime.eq_of_dvd_of_prime</span><span class="w"> </span><span class="o">{</span><span class="n">p</span><span class="w"> </span><span class="n">q</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">}</span> <span class="w"> </span><span class="o">(</span><span class="n">prime_p</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat.Prime</span><span class="w"> </span><span class="n">p</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">prime_q</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat.Prime</span><span class="w"> </span><span class="n">q</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">q</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">q</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">_root_.Nat.Prime.eq_of_dvd_of_prime</span> <span class="o">{</span><span class="n">p</span> <span class="n">q</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">}</span> <span class="o">(</span><span class="n">prime_p</span> <span class="o">:</span> <span class="n">Nat.Prime</span> <span class="n">p</span><span class="o">)</span> <span class="o">(</span><span class="n">prime_q</span> <span class="o">:</span> <span class="n">Nat.Prime</span> <span class="n">q</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">p</span> <span class="bp">∣</span> <span class="n">q</span><span class="o">)</span> <span class="o">:</span> <span class="n">p</span> <span class="bp">=</span> <span class="n">q</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>We can use this lemma to show that if a prime <code class="docutils literal notranslate"><span class="pre">p</span></code> divides a product of a finite
-
@@ -923,15 +919,15 @@ the relevant rewrite rules for the product.In the proof below, the first <code class="docutils literal notranslate"><span class="pre">simp</span></code> applies <code class="docutils literal notranslate"><span class="pre">Finset.prod_empty</span></code>. Step through the beginning of the proof to see the induction unfold, and then finish it off.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">mem_of_dvd_prod_primes</span><span class="w"> </span><span class="o">{</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Finset</span><span class="w"> </span><span class="n">ℕ</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">p</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">prime_p</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">p.Prime</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="o">(</span><span class="bp">∀</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="n">Nat.Prime</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="o">(</span><span class="n">p</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="bp">∏</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">h₀</span><span class="w"> </span><span class="n">h₁</span> <span class="w"> </span><span class="n">induction'</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="n">using</span><span class="w"> </span><span class="n">Finset.induction_on</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="n">ans</span><span class="w"> </span><span class="n">ih</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">h₁</span> <span class="w"> </span><span class="n">linarith</span><span class="w"> </span><span class="o">[</span><span class="n">prime_p.two_le</span><span class="o">]</span> <span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="o">[</span><span class="n">Finset.prod_insert</span><span class="w"> </span><span class="n">ans</span><span class="o">,</span><span class="w"> </span><span class="n">prime_p.dvd_mul</span><span class="o">]</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">h₀</span><span class="w"> </span><span class="n">h₁</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">mem_insert</span><span class="o">]</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">mem_of_dvd_prod_primes</span> <span class="o">{</span><span class="n">s</span> <span class="o">:</span> <span class="n">Finset</span> <span class="n">ℕ</span><span class="o">}</span> <span class="o">{</span><span class="n">p</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">}</span> <span class="o">(</span><span class="n">prime_p</span> <span class="o">:</span> <span class="n">p.Prime</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="bp">∀</span> <span class="n">n</span> <span class="bp">∈</span> <span class="n">s</span><span class="o">,</span> <span class="n">Nat.Prime</span> <span class="n">n</span><span class="o">)</span> <span class="bp">→</span> <span class="o">(</span><span class="n">p</span> <span class="bp">∣</span> <span class="bp">∏</span> <span class="n">n</span> <span class="k">in</span> <span class="n">s</span><span class="o">,</span> <span class="n">n</span><span class="o">)</span> <span class="bp">→</span> <span class="n">p</span> <span class="bp">∈</span> <span class="n">s</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">h₀</span> <span class="n">h₁</span> <span class="n">induction'</span> <span class="n">s</span> <span class="n">using</span> <span class="n">Finset.induction_on</span> <span class="k">with</span> <span class="n">a</span> <span class="n">s</span> <span class="n">ans</span> <span class="n">ih</span> <span class="bp">·</span> <span class="n">simp</span> <span class="n">at</span> <span class="n">h₁</span> <span class="n">linarith</span> <span class="o">[</span><span class="n">prime_p.two_le</span><span class="o">]</span> <span class="n">simp</span> <span class="o">[</span><span class="n">Finset.prod_insert</span> <span class="n">ans</span><span class="o">,</span> <span class="n">prime_p.dvd_mul</span><span class="o">]</span> <span class="n">at</span> <span class="n">h₀</span> <span class="n">h₁</span> <span class="n">rw</span> <span class="o">[</span><span class="n">mem_insert</span><span class="o">]</span> <span class="gr">sorry</span> </pre></div> </div> <p>We need one last property of finite sets.
-
@@ -941,8 +937,8 @@ we wrote <code class="docutils literal notranslate"><span class="pre">{</span> <elements of <code class="docutils literal notranslate"><span class="pre">s</span></code> that satisfy <code class="docutils literal notranslate"><span class="pre">P</span></code>. Given <code class="docutils literal notranslate"><span class="pre">s</span> <span class="pre">:</span> <span class="pre">Finset</span> <span class="pre">α</span></code>, the analogous notion is written <code class="docutils literal notranslate"><span class="pre">s.filter</span> <span class="pre">P</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Finset</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s.filter</span><span class="w"> </span><span class="n">Nat.Prime</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">x.Prime</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">mem_filter</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">s</span> <span class="o">:</span> <span class="n">Finset</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">s.filter</span> <span class="n">Nat.Prime</span> <span class="bp">↔</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">s</span> <span class="bp">∧</span> <span class="n">x.Prime</span> <span class="o">:=</span> <span class="n">mem_filter</span> </pre></div> </div> <p>We now prove an alternative formulation of the statement that there are infinitely many
-
@@ -955,25 +951,25 @@ of the resultleads to the contradiction we are looking for. See if you can complete the sketch below. You can use <code class="docutils literal notranslate"><span class="pre">Finset.prod_pos</span></code> in the proof of the first <code class="docutils literal notranslate"><span class="pre">have</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">primes_infinite'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Finset</span><span class="w"> </span><span class="n">Nat</span><span class="o">,</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">p</span><span class="o">,</span><span class="w"> </span><span class="n">Nat.Prime</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">∉</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">s</span> <span class="w"> </span><span class="n">by_contra</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="n">push_neg</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="n">set</span><span class="w"> </span><span class="n">s'</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">s.filter</span><span class="w"> </span><span class="n">Nat.Prime</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="n">s'_def</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">mem_s'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="o">{</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">},</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s'</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">n.Prime</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">n</span> <span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="o">[</span><span class="n">s'_def</span><span class="o">]</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="o">(</span><span class="bp">∏</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">s'</span><span class="o">,</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">exists_prime_factor</span><span class="w"> </span><span class="n">this</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">p</span><span class="o">,</span><span class="w"> </span><span class="n">pp</span><span class="o">,</span><span class="w"> </span><span class="n">pdvd</span><span class="o">⟩</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="bp">∏</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">s'</span><span class="o">,</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">convert</span><span class="w"> </span><span class="n">Nat.dvd_sub'</span><span class="w"> </span><span class="n">pdvd</span><span class="w"> </span><span class="n">this</span> <span class="w"> </span><span class="n">simp</span> <span class="w"> </span><span class="k">show</span><span class="w"> </span><span class="n">False</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">primes_infinite'</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">s</span> <span class="o">:</span> <span class="n">Finset</span> <span class="n">Nat</span><span class="o">,</span> <span class="bp">∃</span> <span class="n">p</span><span class="o">,</span> <span class="n">Nat.Prime</span> <span class="n">p</span> <span class="bp">∧</span> <span class="n">p</span> <span class="bp">∉</span> <span class="n">s</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">s</span> <span class="n">by_contra</span> <span class="n">h</span> <span class="n">push_neg</span> <span class="n">at</span> <span class="n">h</span> <span class="n">set</span> <span class="n">s'</span> <span class="o">:=</span> <span class="n">s.filter</span> <span class="n">Nat.Prime</span> <span class="k">with</span> <span class="n">s'_def</span> <span class="k">have</span> <span class="n">mem_s'</span> <span class="o">:</span> <span class="bp">∀</span> <span class="o">{</span><span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">},</span> <span class="n">n</span> <span class="bp">∈</span> <span class="n">s'</span> <span class="bp">↔</span> <span class="n">n.Prime</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">n</span> <span class="n">simp</span> <span class="o">[</span><span class="n">s'_def</span><span class="o">]</span> <span class="n">apply</span> <span class="n">h</span> <span class="k">have</span> <span class="o">:</span> <span class="mi">2</span> <span class="bp">≤</span> <span class="o">(</span><span class="bp">∏</span> <span class="n">i</span> <span class="k">in</span> <span class="n">s'</span><span class="o">,</span> <span class="n">i</span><span class="o">)</span> <span class="bp">+</span> <span class="mi">1</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="n">rcases</span> <span class="n">exists_prime_factor</span> <span class="n">this</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">p</span><span class="o">,</span> <span class="n">pp</span><span class="o">,</span> <span class="n">pdvd</span><span class="o">⟩</span> <span class="k">have</span> <span class="o">:</span> <span class="n">p</span> <span class="bp">∣</span> <span class="bp">∏</span> <span class="n">i</span> <span class="k">in</span> <span class="n">s'</span><span class="o">,</span> <span class="n">i</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="k">have</span> <span class="o">:</span> <span class="n">p</span> <span class="bp">∣</span> <span class="mi">1</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">convert</span> <span class="n">Nat.dvd_sub'</span> <span class="n">pdvd</span> <span class="n">this</span> <span class="n">simp</span> <span class="k">show</span> <span class="n">False</span> <span class="gr">sorry</span> </pre></div> </div> <p>We have thus seen two ways of saying that there are infinitely many primes:
-
@@ -989,22 +985,22 @@ we can dispense with the assumption.</p>ranges over <code class="docutils literal notranslate"><span class="pre">s</span></code>, returning <code class="docutils literal notranslate"><span class="pre">0</span></code> in the case where <code class="docutils literal notranslate"><span class="pre">s</span></code> is empty and the codomain of <code class="docutils literal notranslate"><span class="pre">f</span></code> is <code class="docutils literal notranslate"><span class="pre">ℕ</span></code>. In the first proof, we use <code class="docutils literal notranslate"><span class="pre">s.sup</span> <span class="pre">id</span></code>, where <code class="docutils literal notranslate"><span class="pre">id</span></code> is the identity function, to refer to the maximum value in <code class="docutils literal notranslate"><span class="pre">s</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">bounded_of_ex_finset</span><span class="w"> </span><span class="o">(</span><span class="n">Q</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="kt">Prop</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="o">(</span><span class="bp">∃</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Finset</span><span class="w"> </span><span class="n">ℕ</span><span class="o">,</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">k</span><span class="o">,</span><span class="w"> </span><span class="n">Q</span><span class="w"> </span><span class="n">k</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">k</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="o">)</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">k</span><span class="o">,</span><span class="w"> </span><span class="n">Q</span><span class="w"> </span><span class="n">k</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">k</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rintro</span><span class="w"> </span><span class="o">⟨</span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="n">hs</span><span class="o">⟩</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">s.sup</span><span class="w"> </span><span class="n">id</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">k</span><span class="w"> </span><span class="n">Qk</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">Nat.lt_succ_of_le</span> <span class="w"> </span><span class="k">show</span><span class="w"> </span><span class="n">id</span><span class="w"> </span><span class="n">k</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">s.sup</span><span class="w"> </span><span class="n">id</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">le_sup</span><span class="w"> </span><span class="o">(</span><span class="n">hs</span><span class="w"> </span><span class="n">k</span><span class="w"> </span><span class="n">Qk</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">bounded_of_ex_finset</span> <span class="o">(</span><span class="n">Q</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="kt">Prop</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="bp">∃</span> <span class="n">s</span> <span class="o">:</span> <span class="n">Finset</span> <span class="n">ℕ</span><span class="o">,</span> <span class="bp">∀</span> <span class="n">k</span><span class="o">,</span> <span class="n">Q</span> <span class="n">k</span> <span class="bp">→</span> <span class="n">k</span> <span class="bp">∈</span> <span class="n">s</span><span class="o">)</span> <span class="bp">→</span> <span class="bp">∃</span> <span class="n">n</span><span class="o">,</span> <span class="bp">∀</span> <span class="n">k</span><span class="o">,</span> <span class="n">Q</span> <span class="n">k</span> <span class="bp">→</span> <span class="n">k</span> <span class="bp"><</span> <span class="n">n</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rintro</span> <span class="o">⟨</span><span class="n">s</span><span class="o">,</span> <span class="n">hs</span><span class="o">⟩</span> <span class="n">use</span> <span class="n">s.sup</span> <span class="n">id</span> <span class="bp">+</span> <span class="mi">1</span> <span class="n">intro</span> <span class="n">k</span> <span class="n">Qk</span> <span class="n">apply</span> <span class="n">Nat.lt_succ_of_le</span> <span class="k">show</span> <span class="n">id</span> <span class="n">k</span> <span class="bp">≤</span> <span class="n">s.sup</span> <span class="n">id</span> <span class="n">apply</span> <span class="n">le_sup</span> <span class="o">(</span><span class="n">hs</span> <span class="n">k</span> <span class="n">Qk</span><span class="o">)</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">ex_finset_of_bounded</span><span class="w"> </span><span class="o">(</span><span class="n">Q</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="kt">Prop</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">DecidablePred</span><span class="w"> </span><span class="n">Q</span><span class="o">]</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="o">(</span><span class="bp">∃</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">k</span><span class="o">,</span><span class="w"> </span><span class="n">Q</span><span class="w"> </span><span class="n">k</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">k</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Finset</span><span class="w"> </span><span class="n">ℕ</span><span class="o">,</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">k</span><span class="o">,</span><span class="w"> </span><span class="n">Q</span><span class="w"> </span><span class="n">k</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">k</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rintro</span><span class="w"> </span><span class="o">⟨</span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="n">hn</span><span class="o">⟩</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="o">(</span><span class="n">range</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="o">))</span><span class="bp">.</span><span class="n">filter</span><span class="w"> </span><span class="n">Q</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">k</span> <span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="o">[</span><span class="n">Nat.lt_succ_iff</span><span class="o">]</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">hn</span><span class="w"> </span><span class="n">k</span> <span class="kd">theorem</span> <span class="n">ex_finset_of_bounded</span> <span class="o">(</span><span class="n">Q</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="kt">Prop</span><span class="o">)</span> <span class="o">[</span><span class="n">DecidablePred</span> <span class="n">Q</span><span class="o">]</span> <span class="o">:</span> <span class="o">(</span><span class="bp">∃</span> <span class="n">n</span><span class="o">,</span> <span class="bp">∀</span> <span class="n">k</span><span class="o">,</span> <span class="n">Q</span> <span class="n">k</span> <span class="bp">→</span> <span class="n">k</span> <span class="bp">≤</span> <span class="n">n</span><span class="o">)</span> <span class="bp">→</span> <span class="bp">∃</span> <span class="n">s</span> <span class="o">:</span> <span class="n">Finset</span> <span class="n">ℕ</span><span class="o">,</span> <span class="bp">∀</span> <span class="n">k</span><span class="o">,</span> <span class="n">Q</span> <span class="n">k</span> <span class="bp">↔</span> <span class="n">k</span> <span class="bp">∈</span> <span class="n">s</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rintro</span> <span class="o">⟨</span><span class="n">n</span><span class="o">,</span> <span class="n">hn</span><span class="o">⟩</span> <span class="n">use</span> <span class="o">(</span><span class="n">range</span> <span class="o">(</span><span class="n">n</span> <span class="bp">+</span> <span class="mi">1</span><span class="o">))</span><span class="bp">.</span><span class="n">filter</span> <span class="n">Q</span> <span class="n">intro</span> <span class="n">k</span> <span class="n">simp</span> <span class="o">[</span><span class="n">Nat.lt_succ_iff</span><span class="o">]</span> <span class="n">exact</span> <span class="n">hn</span> <span class="n">k</span> </pre></div> </div> <p>A small variation on our second proof that there are infinitely many primes
-
@@ -1034,7 +1030,7 @@ But in that case, <span class="math notranslate nohighlight">\(p\)</span> divideand hence 3, which contradicts the fact that it is not 3.</p> <p>In Lean, the notation <code class="docutils literal notranslate"><span class="pre">n</span> <span class="pre">%</span> <span class="pre">m</span></code>, read “<code class="docutils literal notranslate"><span class="pre">n</span></code> modulo <code class="docutils literal notranslate"><span class="pre">m</span></code>,” denotes the remainder of the division of <code class="docutils literal notranslate"><span class="pre">n</span></code> by <code class="docutils literal notranslate"><span class="pre">m</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">27</span><span class="w"> </span><span class="bp">%</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">norm_num</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="mi">27</span> <span class="bp">%</span> <span class="mi">4</span> <span class="bp">=</span> <span class="mi">3</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">norm_num</span> </pre></div> </div> <p>We can then render the statement “<code class="docutils literal notranslate"><span class="pre">n</span></code> is congruent to 3 modulo 4”
-
@@ -1045,66 +1041,66 @@ a small number of cases.In the second named theorem, remember that the semicolon means that the subsequent tactic block is applied to all the goals created by the preceding tactic.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="mi">4</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">3</span><span class="o">)</span><span class="w"> </span><span class="bp">%</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">add_comm</span><span class="o">,</span><span class="w"> </span><span class="n">Nat.add_mul_mod_self_left</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="mi">4</span> <span class="bp">*</span> <span class="n">n</span> <span class="bp">+</span> <span class="mi">3</span><span class="o">)</span> <span class="bp">%</span> <span class="mi">4</span> <span class="bp">=</span> <span class="mi">3</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">add_comm</span><span class="o">,</span> <span class="n">Nat.add_mul_mod_self_left</span><span class="o">]</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">mod_4_eq_3_or_mod_4_eq_3</span><span class="w"> </span><span class="o">{</span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">%</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">3</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">%</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="bp">∨</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">%</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">revert</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">Nat.mul_mod</span><span class="o">]</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">%</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Nat.mod_lt</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="o">(</span><span class="kd">by</span><span class="w"> </span><span class="n">norm_num</span><span class="o">)</span> <span class="w"> </span><span class="n">interval_cases</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">%</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="o">[</span><span class="bp">-</span><span class="n">Nat.mul_mod_mod</span><span class="o">]</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">%</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Nat.mod_lt</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">(</span><span class="kd">by</span><span class="w"> </span><span class="n">norm_num</span><span class="o">)</span> <span class="w"> </span><span class="n">interval_cases</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">%</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">simp</span> <span class="kd">theorem</span> <span class="n">mod_4_eq_3_or_mod_4_eq_3</span> <span class="o">{</span><span class="n">m</span> <span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">m</span> <span class="bp">*</span> <span class="n">n</span> <span class="bp">%</span> <span class="mi">4</span> <span class="bp">=</span> <span class="mi">3</span><span class="o">)</span> <span class="o">:</span> <span class="n">m</span> <span class="bp">%</span> <span class="mi">4</span> <span class="bp">=</span> <span class="mi">3</span> <span class="bp">∨</span> <span class="n">n</span> <span class="bp">%</span> <span class="mi">4</span> <span class="bp">=</span> <span class="mi">3</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">revert</span> <span class="n">h</span> <span class="n">rw</span> <span class="o">[</span><span class="n">Nat.mul_mod</span><span class="o">]</span> <span class="k">have</span> <span class="o">:</span> <span class="n">m</span> <span class="bp">%</span> <span class="mi">4</span> <span class="bp"><</span> <span class="mi">4</span> <span class="o">:=</span> <span class="n">Nat.mod_lt</span> <span class="n">m</span> <span class="o">(</span><span class="kd">by</span> <span class="n">norm_num</span><span class="o">)</span> <span class="n">interval_cases</span> <span class="n">m</span> <span class="bp">%</span> <span class="mi">4</span> <span class="bp"><;></span> <span class="n">simp</span> <span class="o">[</span><span class="bp">-</span><span class="n">Nat.mul_mod_mod</span><span class="o">]</span> <span class="k">have</span> <span class="o">:</span> <span class="n">n</span> <span class="bp">%</span> <span class="mi">4</span> <span class="bp"><</span> <span class="mi">4</span> <span class="o">:=</span> <span class="n">Nat.mod_lt</span> <span class="n">n</span> <span class="o">(</span><span class="kd">by</span> <span class="n">norm_num</span><span class="o">)</span> <span class="n">interval_cases</span> <span class="n">n</span> <span class="bp">%</span> <span class="mi">4</span> <span class="bp"><;></span> <span class="n">simp</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">two_le_of_mod_4_eq_3</span><span class="w"> </span><span class="o">{</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">%</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">3</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">two_le</span><span class="w"> </span><span class="bp"><;></span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">neq</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">neq</span><span class="o">]</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="n">norm_num</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">h</span> <span class="kd">theorem</span> <span class="n">two_le_of_mod_4_eq_3</span> <span class="o">{</span><span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">n</span> <span class="bp">%</span> <span class="mi">4</span> <span class="bp">=</span> <span class="mi">3</span><span class="o">)</span> <span class="o">:</span> <span class="mi">2</span> <span class="bp">≤</span> <span class="n">n</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">apply</span> <span class="n">two_le</span> <span class="bp"><;></span> <span class="bp">·</span> <span class="n">intro</span> <span class="n">neq</span> <span class="n">rw</span> <span class="o">[</span><span class="n">neq</span><span class="o">]</span> <span class="n">at</span> <span class="n">h</span> <span class="n">norm_num</span> <span class="n">at</span> <span class="n">h</span> </pre></div> </div> <p>We will also need the following fact, which says that if <code class="docutils literal notranslate"><span class="pre">m</span></code> is a nontrivial divisor of <code class="docutils literal notranslate"><span class="pre">n</span></code>, then so is <code class="docutils literal notranslate"><span class="pre">n</span> <span class="pre">/</span> <span class="pre">m</span></code>. See if you can complete the proof using <code class="docutils literal notranslate"><span class="pre">Nat.div_dvd_of_dvd</span></code> and <code class="docutils literal notranslate"><span class="pre">Nat.div_lt_self</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">aux</span><span class="w"> </span><span class="o">{</span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h₀</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h₁</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">m</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h₂</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">aux</span> <span class="o">{</span><span class="n">m</span> <span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">}</span> <span class="o">(</span><span class="n">h₀</span> <span class="o">:</span> <span class="n">m</span> <span class="bp">∣</span> <span class="n">n</span><span class="o">)</span> <span class="o">(</span><span class="n">h₁</span> <span class="o">:</span> <span class="mi">2</span> <span class="bp">≤</span> <span class="n">m</span><span class="o">)</span> <span class="o">(</span><span class="n">h₂</span> <span class="o">:</span> <span class="n">m</span> <span class="bp"><</span> <span class="n">n</span><span class="o">)</span> <span class="o">:</span> <span class="n">n</span> <span class="bp">/</span> <span class="n">m</span> <span class="bp">∣</span> <span class="n">n</span> <span class="bp">∧</span> <span class="n">n</span> <span class="bp">/</span> <span class="n">m</span> <span class="bp"><</span> <span class="n">n</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>Now put all the pieces together to prove that any number congruent to 3 modulo 4 has a prime divisor with that same property.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">exists_prime_factor_mod_4_eq_3</span><span class="w"> </span><span class="o">{</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">%</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">3</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat</span><span class="o">,</span><span class="w"> </span><span class="n">p.Prime</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">%</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">by_cases</span><span class="w"> </span><span class="n">np</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">n.Prime</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">n</span> <span class="w"> </span><span class="n">induction'</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">using</span><span class="w"> </span><span class="n">Nat.strong_induction_on</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">ih</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">Nat.prime_def_lt</span><span class="o">]</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">np</span> <span class="w"> </span><span class="n">push_neg</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">np</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">np</span><span class="w"> </span><span class="o">(</span><span class="n">two_le_of_mod_4_eq_3</span><span class="w"> </span><span class="n">h</span><span class="o">)</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">m</span><span class="o">,</span><span class="w"> </span><span class="n">mltn</span><span class="o">,</span><span class="w"> </span><span class="n">mdvdn</span><span class="o">,</span><span class="w"> </span><span class="n">mne1</span><span class="o">⟩</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">mge2</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">two_le</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="n">mne1</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">mz</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">mz</span><span class="o">,</span><span class="w"> </span><span class="n">zero_dvd_iff</span><span class="o">]</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">mdvdn</span> <span class="w"> </span><span class="n">linarith</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">neq</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="n">m</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Nat.mul_div_cancel'</span><span class="w"> </span><span class="n">mdvdn</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">%</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="bp">∨</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">%</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">mod_4_eq_3_or_mod_4_eq_3</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">neq</span><span class="o">,</span><span class="w"> </span><span class="n">h</span><span class="o">]</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">this</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="n">h1</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">h1</span> <span class="w"> </span><span class="bp">.</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="bp">.</span><span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">exists_prime_factor_mod_4_eq_3</span> <span class="o">{</span><span class="n">n</span> <span class="o">:</span> <span class="n">Nat</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">n</span> <span class="bp">%</span> <span class="mi">4</span> <span class="bp">=</span> <span class="mi">3</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">p</span> <span class="o">:</span> <span class="n">Nat</span><span class="o">,</span> <span class="n">p.Prime</span> <span class="bp">∧</span> <span class="n">p</span> <span class="bp">∣</span> <span class="n">n</span> <span class="bp">∧</span> <span class="n">p</span> <span class="bp">%</span> <span class="mi">4</span> <span class="bp">=</span> <span class="mi">3</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">by_cases</span> <span class="n">np</span> <span class="o">:</span> <span class="n">n.Prime</span> <span class="bp">·</span> <span class="n">use</span> <span class="n">n</span> <span class="n">induction'</span> <span class="n">n</span> <span class="n">using</span> <span class="n">Nat.strong_induction_on</span> <span class="k">with</span> <span class="n">n</span> <span class="n">ih</span> <span class="n">rw</span> <span class="o">[</span><span class="n">Nat.prime_def_lt</span><span class="o">]</span> <span class="n">at</span> <span class="n">np</span> <span class="n">push_neg</span> <span class="n">at</span> <span class="n">np</span> <span class="n">rcases</span> <span class="n">np</span> <span class="o">(</span><span class="n">two_le_of_mod_4_eq_3</span> <span class="n">h</span><span class="o">)</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">m</span><span class="o">,</span> <span class="n">mltn</span><span class="o">,</span> <span class="n">mdvdn</span><span class="o">,</span> <span class="n">mne1</span><span class="o">⟩</span> <span class="k">have</span> <span class="n">mge2</span> <span class="o">:</span> <span class="mi">2</span> <span class="bp">≤</span> <span class="n">m</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">apply</span> <span class="n">two_le</span> <span class="n">_</span> <span class="n">mne1</span> <span class="n">intro</span> <span class="n">mz</span> <span class="n">rw</span> <span class="o">[</span><span class="n">mz</span><span class="o">,</span> <span class="n">zero_dvd_iff</span><span class="o">]</span> <span class="n">at</span> <span class="n">mdvdn</span> <span class="n">linarith</span> <span class="k">have</span> <span class="n">neq</span> <span class="o">:</span> <span class="n">m</span> <span class="bp">*</span> <span class="o">(</span><span class="n">n</span> <span class="bp">/</span> <span class="n">m</span><span class="o">)</span> <span class="bp">=</span> <span class="n">n</span> <span class="o">:=</span> <span class="n">Nat.mul_div_cancel'</span> <span class="n">mdvdn</span> <span class="k">have</span> <span class="o">:</span> <span class="n">m</span> <span class="bp">%</span> <span class="mi">4</span> <span class="bp">=</span> <span class="mi">3</span> <span class="bp">∨</span> <span class="n">n</span> <span class="bp">/</span> <span class="n">m</span> <span class="bp">%</span> <span class="mi">4</span> <span class="bp">=</span> <span class="mi">3</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">apply</span> <span class="n">mod_4_eq_3_or_mod_4_eq_3</span> <span class="n">rw</span> <span class="o">[</span><span class="n">neq</span><span class="o">,</span> <span class="n">h</span><span class="o">]</span> <span class="n">rcases</span> <span class="n">this</span> <span class="k">with</span> <span class="n">h1</span> <span class="bp">|</span> <span class="n">h1</span> <span class="bp">.</span> <span class="gr">sorry</span> <span class="bp">.</span> <span class="gr">sorry</span> </pre></div> </div> <p>We are in the home stretch. Given a set <code class="docutils literal notranslate"><span class="pre">s</span></code> of prime numbers, we need to talk about the result of removing 3 from that set, if it is present. The function <code class="docutils literal notranslate"><span class="pre">Finset.erase</span></code> handles that.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Finset</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">erase</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rwa</span><span class="w"> </span><span class="o">[</span><span class="n">mem_erase</span><span class="o">]</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">h</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">m</span> <span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">(</span><span class="n">s</span> <span class="o">:</span> <span class="n">Finset</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">m</span> <span class="bp">∈</span> <span class="n">erase</span> <span class="n">s</span> <span class="n">n</span><span class="o">)</span> <span class="o">:</span> <span class="n">m</span> <span class="bp">≠</span> <span class="n">n</span> <span class="bp">∧</span> <span class="n">m</span> <span class="bp">∈</span> <span class="n">s</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rwa</span> <span class="o">[</span><span class="n">mem_erase</span><span class="o">]</span> <span class="n">at</span> <span class="n">h</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Finset</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">erase</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="n">assumption</span> <span class="kd">example</span> <span class="o">(</span><span class="n">m</span> <span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">(</span><span class="n">s</span> <span class="o">:</span> <span class="n">Finset</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">m</span> <span class="bp">∈</span> <span class="n">erase</span> <span class="n">s</span> <span class="n">n</span><span class="o">)</span> <span class="o">:</span> <span class="n">m</span> <span class="bp">≠</span> <span class="n">n</span> <span class="bp">∧</span> <span class="n">m</span> <span class="bp">∈</span> <span class="n">s</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> <span class="n">at</span> <span class="n">h</span> <span class="n">assumption</span> </pre></div> </div> <p>We are now ready to prove that there are infinitely many primes
-
@@ -1112,31 +1108,31 @@ congruent to 3 modulo 4.Fill in the missing parts below. Our solution uses <code class="docutils literal notranslate"><span class="pre">Nat.dvd_add_iff_left</span></code> and <code class="docutils literal notranslate"><span class="pre">Nat.dvd_sub'</span></code> along the way.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">primes_mod_4_eq_3_infinite</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="n">Nat.Prime</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">%</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">by_contra</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="n">push_neg</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="n">hn</span><span class="o">⟩</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Finset</span><span class="w"> </span><span class="n">Nat</span><span class="o">,</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">,</span><span class="w"> </span><span class="n">p.Prime</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">%</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">ex_finset_of_bounded</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">n</span> <span class="w"> </span><span class="n">contrapose</span><span class="bp">!</span><span class="w"> </span><span class="n">hn</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">hn</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">p</span><span class="o">,</span><span class="w"> </span><span class="o">⟨</span><span class="n">pp</span><span class="o">,</span><span class="w"> </span><span class="n">p4</span><span class="o">⟩,</span><span class="w"> </span><span class="n">pltn</span><span class="o">⟩</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="o">⟨</span><span class="n">p</span><span class="o">,</span><span class="w"> </span><span class="n">pltn</span><span class="o">,</span><span class="w"> </span><span class="n">pp</span><span class="o">,</span><span class="w"> </span><span class="n">p4</span><span class="o">⟩</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">this</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="n">hs</span><span class="o">⟩</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">h₁</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">((</span><span class="mi">4</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="bp">∏</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">erase</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="mi">3</span><span class="o">,</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">3</span><span class="o">)</span><span class="w"> </span><span class="bp">%</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">exists_prime_factor_mod_4_eq_3</span><span class="w"> </span><span class="n">h₁</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">p</span><span class="o">,</span><span class="w"> </span><span class="n">pp</span><span class="o">,</span><span class="w"> </span><span class="n">pdvd</span><span class="o">,</span><span class="w"> </span><span class="n">p4eq</span><span class="o">⟩</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">ps</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">pne3</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="bp">∏</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">erase</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="mi">3</span><span class="o">,</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">contradiction</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">primes_mod_4_eq_3_infinite</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">n</span><span class="o">,</span> <span class="bp">∃</span> <span class="n">p</span> <span class="bp">></span> <span class="n">n</span><span class="o">,</span> <span class="n">Nat.Prime</span> <span class="n">p</span> <span class="bp">∧</span> <span class="n">p</span> <span class="bp">%</span> <span class="mi">4</span> <span class="bp">=</span> <span class="mi">3</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">by_contra</span> <span class="n">h</span> <span class="n">push_neg</span> <span class="n">at</span> <span class="n">h</span> <span class="n">rcases</span> <span class="n">h</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">n</span><span class="o">,</span> <span class="n">hn</span><span class="o">⟩</span> <span class="k">have</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">s</span> <span class="o">:</span> <span class="n">Finset</span> <span class="n">Nat</span><span class="o">,</span> <span class="bp">∀</span> <span class="n">p</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">,</span> <span class="n">p.Prime</span> <span class="bp">∧</span> <span class="n">p</span> <span class="bp">%</span> <span class="mi">4</span> <span class="bp">=</span> <span class="mi">3</span> <span class="bp">↔</span> <span class="n">p</span> <span class="bp">∈</span> <span class="n">s</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">apply</span> <span class="n">ex_finset_of_bounded</span> <span class="n">use</span> <span class="n">n</span> <span class="n">contrapose</span><span class="bp">!</span> <span class="n">hn</span> <span class="n">rcases</span> <span class="n">hn</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">p</span><span class="o">,</span> <span class="o">⟨</span><span class="n">pp</span><span class="o">,</span> <span class="n">p4</span><span class="o">⟩,</span> <span class="n">pltn</span><span class="o">⟩</span> <span class="n">exact</span> <span class="o">⟨</span><span class="n">p</span><span class="o">,</span> <span class="n">pltn</span><span class="o">,</span> <span class="n">pp</span><span class="o">,</span> <span class="n">p4</span><span class="o">⟩</span> <span class="n">rcases</span> <span class="n">this</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">s</span><span class="o">,</span> <span class="n">hs</span><span class="o">⟩</span> <span class="k">have</span> <span class="n">h₁</span> <span class="o">:</span> <span class="o">((</span><span class="mi">4</span> <span class="bp">*</span> <span class="bp">∏</span> <span class="n">i</span> <span class="k">in</span> <span class="n">erase</span> <span class="n">s</span> <span class="mi">3</span><span class="o">,</span> <span class="n">i</span><span class="o">)</span> <span class="bp">+</span> <span class="mi">3</span><span class="o">)</span> <span class="bp">%</span> <span class="mi">4</span> <span class="bp">=</span> <span class="mi">3</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="n">rcases</span> <span class="n">exists_prime_factor_mod_4_eq_3</span> <span class="n">h₁</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">p</span><span class="o">,</span> <span class="n">pp</span><span class="o">,</span> <span class="n">pdvd</span><span class="o">,</span> <span class="n">p4eq</span><span class="o">⟩</span> <span class="k">have</span> <span class="n">ps</span> <span class="o">:</span> <span class="n">p</span> <span class="bp">∈</span> <span class="n">s</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="k">have</span> <span class="n">pne3</span> <span class="o">:</span> <span class="n">p</span> <span class="bp">≠</span> <span class="mi">3</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="k">have</span> <span class="o">:</span> <span class="n">p</span> <span class="bp">∣</span> <span class="mi">4</span> <span class="bp">*</span> <span class="bp">∏</span> <span class="n">i</span> <span class="k">in</span> <span class="n">erase</span> <span class="n">s</span> <span class="mi">3</span><span class="o">,</span> <span class="n">i</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="k">have</span> <span class="o">:</span> <span class="n">p</span> <span class="bp">∣</span> <span class="mi">3</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="k">have</span> <span class="o">:</span> <span class="n">p</span> <span class="bp">=</span> <span class="mi">3</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="n">contradiction</span> </pre></div> </div> <p>If you managed to complete the proof, congratulations! This has been a serious
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@@ -93,7 +89,7 @@<div itemprop="articleBody"> <section id="structures"> <span id="id1"></span><h1><span class="section-number">6. </span>Structures<a class="headerlink" href="#structures" title="Link to this heading"></a></h1> <span id="id1"></span><h1><span class="section-number">6. </span>Structures<a class="headerlink" href="#structures" title="Permalink to this heading"></a></h1> <p>Modern mathematics makes essential use of algebraic structures, which encapsulate patterns that can be instantiated in
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@@ -113,42 +109,42 @@ algebraic structures on your own.</p><p>For more technical detail, you can consult <a class="reference external" href="https://leanprover.github.io/theorem_proving_in_lean/">Theorem Proving in Lean</a>, and a paper by Anne Baanen, <a class="reference external" href="https://arxiv.org/abs/2202.01629">Use and abuse of instance parameters in the Lean mathematical library</a>.</p> <section id="defining-structures"> <span id="section-structures"></span><h2><span class="section-number">6.1. </span>Defining structures<a class="headerlink" href="#defining-structures" title="Link to this heading"></a></h2> <span id="section-structures"></span><h2><span class="section-number">6.1. </span>Defining structures<a class="headerlink" href="#defining-structures" title="Permalink to this heading"></a></h2> <p>In the broadest sense of the term, a <em>structure</em> is a specification of a collection of data, possibly with constraints that the data is required to satisfy. An <em>instance</em> of the structure is a particular bundle of data satisfying the constraints. For example, we can specify that a point is a tuple of three real numbers:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">@[</span><span class="n">ext</span><span class="kd">]</span> <span class="kd">structure</span><span class="w"> </span><span class="n">Point</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span> <span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span> <span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">@[ext]</span> <span class="kd">structure</span> <span class="n">Point</span> <span class="n">where</span> <span class="n">x</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="n">z</span> <span class="o">:</span> <span class="n">ℝ</span> </pre></div> </div> <p>The <code class="docutils literal notranslate"><span class="pre">@[ext]</span></code> annotation tells Lean to automatically generate theorems that can be used to prove that two instances of a structure are equal when their components are equal, a property known as <em>extensionality</em>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="n">Point.ext</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="n">Point.ext</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Point</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hx</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a.x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">b.x</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hy</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a.y</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">b.y</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hz</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a.z</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">b.z</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">ext</span> <span class="w"> </span><span class="n">repeat'</span><span class="w"> </span><span class="n">assumption</span> <span class="kd">example</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">Point</span><span class="o">)</span> <span class="o">(</span><span class="n">hx</span> <span class="o">:</span> <span class="n">a.x</span> <span class="bp">=</span> <span class="n">b.x</span><span class="o">)</span> <span class="o">(</span><span class="n">hy</span> <span class="o">:</span> <span class="n">a.y</span> <span class="bp">=</span> <span class="n">b.y</span><span class="o">)</span> <span class="o">(</span><span class="n">hz</span> <span class="o">:</span> <span class="n">a.z</span> <span class="bp">=</span> <span class="n">b.z</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">=</span> <span class="n">b</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">ext</span> <span class="n">repeat'</span> <span class="n">assumption</span> </pre></div> </div> <p>We can then define particular instances of the <code class="docutils literal notranslate"><span class="pre">Point</span></code> structure. Lean provides multiple ways of doing that.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">myPoint1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Point</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="mi">2</span> <span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="bp">-</span><span class="mi">1</span> <span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="mi">4</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">myPoint1</span> <span class="o">:</span> <span class="n">Point</span> <span class="n">where</span> <span class="n">x</span> <span class="o">:=</span> <span class="mi">2</span> <span class="n">y</span> <span class="o">:=</span> <span class="bp">-</span><span class="mi">1</span> <span class="n">z</span> <span class="o">:=</span> <span class="mi">4</span> <span class="kd">def</span><span class="w"> </span><span class="n">myPoint2</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Point</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">⟨</span><span class="mi">2</span><span class="o">,</span><span class="w"> </span><span class="bp">-</span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="mi">4</span><span class="o">⟩</span> <span class="kd">def</span> <span class="n">myPoint2</span> <span class="o">:</span> <span class="n">Point</span> <span class="o">:=</span> <span class="o">⟨</span><span class="mi">2</span><span class="o">,</span> <span class="bp">-</span><span class="mi">1</span><span class="o">,</span> <span class="mi">4</span><span class="o">⟩</span> <span class="kd">def</span><span class="w"> </span><span class="n">myPoint3</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Point.mk</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">(</span><span class="bp">-</span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="mi">4</span> <span class="kd">def</span> <span class="n">myPoint3</span> <span class="o">:=</span> <span class="n">Point.mk</span> <span class="mi">2</span> <span class="o">(</span><span class="bp">-</span><span class="mi">1</span><span class="o">)</span> <span class="mi">4</span> </pre></div> </div> <p>In the first example, the fields of the structure are named
-
@@ -157,12 +153,12 @@ The function <code class="docutils literal notranslate"><span class="pre">Point.is known as the <em>constructor</em> for the <code class="docutils literal notranslate"><span class="pre">Point</span></code> structure, because it serves to construct elements. You can specify a different name if you want, like <code class="docutils literal notranslate"><span class="pre">build</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">structure</span><span class="w"> </span><span class="n">Point'</span><span class="w"> </span><span class="n">where</span><span class="w"> </span><span class="n">build</span><span class="w"> </span><span class="o">::</span> <span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span> <span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span> <span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">structure</span> <span class="n">Point'</span> <span class="n">where</span> <span class="n">build</span> <span class="o">::</span> <span class="n">x</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="n">z</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="k">#check</span><span class="w"> </span><span class="n">Point'.build</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">(</span><span class="bp">-</span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="mi">4</span> <span class="k">#check</span> <span class="n">Point'.build</span> <span class="mi">2</span> <span class="o">(</span><span class="bp">-</span><span class="mi">1</span><span class="o">)</span> <span class="mi">4</span> </pre></div> </div> <p>The next two examples show how to define functions on structures.
-
@@ -180,23 +176,23 @@ But remember that it is often convenient to useanonymous projection notation, which allows us to write <code class="docutils literal notranslate"><span class="pre">a.add</span> <span class="pre">b</span></code> instead of <code class="docutils literal notranslate"><span class="pre">Point.add</span> <span class="pre">a</span> <span class="pre">b</span></code>. Lean interprets the former as the latter because <code class="docutils literal notranslate"><span class="pre">a</span></code> has type <code class="docutils literal notranslate"><span class="pre">Point</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">namespace</span><span class="w"> </span><span class="n">Point</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">namespace</span> <span class="n">Point</span> <span class="kd">def</span><span class="w"> </span><span class="n">add</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Point</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Point</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">⟨</span><span class="n">a.x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b.x</span><span class="o">,</span><span class="w"> </span><span class="n">a.y</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b.y</span><span class="o">,</span><span class="w"> </span><span class="n">a.z</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b.z</span><span class="o">⟩</span> <span class="kd">def</span> <span class="n">add</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">Point</span><span class="o">)</span> <span class="o">:</span> <span class="n">Point</span> <span class="o">:=</span> <span class="o">⟨</span><span class="n">a.x</span> <span class="bp">+</span> <span class="n">b.x</span><span class="o">,</span> <span class="n">a.y</span> <span class="bp">+</span> <span class="n">b.y</span><span class="o">,</span> <span class="n">a.z</span> <span class="bp">+</span> <span class="n">b.z</span><span class="o">⟩</span> <span class="kd">def</span><span class="w"> </span><span class="n">add'</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Point</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Point</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">a.x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b.x</span> <span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">a.y</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b.y</span> <span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">a.z</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b.z</span> <span class="kd">def</span> <span class="n">add'</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">Point</span><span class="o">)</span> <span class="o">:</span> <span class="n">Point</span> <span class="n">where</span> <span class="n">x</span> <span class="o">:=</span> <span class="n">a.x</span> <span class="bp">+</span> <span class="n">b.x</span> <span class="n">y</span> <span class="o">:=</span> <span class="n">a.y</span> <span class="bp">+</span> <span class="n">b.y</span> <span class="n">z</span> <span class="o">:=</span> <span class="n">a.z</span> <span class="bp">+</span> <span class="n">b.z</span> <span class="k">#check</span><span class="w"> </span><span class="n">add</span><span class="w"> </span><span class="n">myPoint1</span><span class="w"> </span><span class="n">myPoint2</span> <span class="k">#check</span><span class="w"> </span><span class="n">myPoint1.add</span><span class="w"> </span><span class="n">myPoint2</span> <span class="k">#check</span> <span class="n">add</span> <span class="n">myPoint1</span> <span class="n">myPoint2</span> <span class="k">#check</span> <span class="n">myPoint1.add</span> <span class="n">myPoint2</span> <span class="kd">end</span><span class="w"> </span><span class="n">Point</span> <span class="kd">end</span> <span class="n">Point</span> <span class="k">#check</span><span class="w"> </span><span class="n">Point.add</span><span class="w"> </span><span class="n">myPoint1</span><span class="w"> </span><span class="n">myPoint2</span> <span class="k">#check</span><span class="w"> </span><span class="n">myPoint1.add</span><span class="w"> </span><span class="n">myPoint2</span> <span class="k">#check</span> <span class="n">Point.add</span> <span class="n">myPoint1</span> <span class="n">myPoint2</span> <span class="k">#check</span> <span class="n">myPoint1.add</span> <span class="n">myPoint2</span> </pre></div> </div> <p>Below we will continue to put definitions in the relevant
-
@@ -209,18 +205,18 @@ Below we use the <code class="docutils literal notranslate"><span class="pre">prtheorem is <code class="docutils literal notranslate"><span class="pre">Point.add_comm</span></code>, even when the namespace is open. This is helpful when we want to avoid ambiguity with a generic theorem like <code class="docutils literal notranslate"><span class="pre">add_comm</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">protected</span><span class="w"> </span><span class="kd">theorem</span><span class="w"> </span><span class="n">add_comm</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Point</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">add</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">add</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">add</span><span class="o">,</span><span class="w"> </span><span class="n">add</span><span class="o">]</span> <span class="w"> </span><span class="n">ext</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">dsimp</span> <span class="w"> </span><span class="n">repeat'</span><span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">add_comm</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">protected</span> <span class="kd">theorem</span> <span class="n">add_comm</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">Point</span><span class="o">)</span> <span class="o">:</span> <span class="n">add</span> <span class="n">a</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">add</span> <span class="n">b</span> <span class="n">a</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">add</span><span class="o">,</span> <span class="n">add</span><span class="o">]</span> <span class="n">ext</span> <span class="bp"><;></span> <span class="n">dsimp</span> <span class="n">repeat'</span> <span class="n">apply</span> <span class="n">add_comm</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Point</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">add</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">add</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="o">[</span><span class="n">add</span><span class="o">,</span><span class="w"> </span><span class="n">add_comm</span><span class="o">]</span> <span class="kd">example</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">Point</span><span class="o">)</span> <span class="o">:</span> <span class="n">add</span> <span class="n">a</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">add</span> <span class="n">b</span> <span class="n">a</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> <span class="o">[</span><span class="n">add</span><span class="o">,</span> <span class="n">add_comm</span><span class="o">]</span> </pre></div> </div> <p>Because Lean can unfold definitions and simplify projections internally, sometimes the equations we want hold definitionally.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">add_x</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Point</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">a.add</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="bp">.</span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a.x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b.x</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">add_x</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">Point</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">a.add</span> <span class="n">b</span><span class="o">)</span><span class="bp">.</span><span class="n">x</span> <span class="bp">=</span> <span class="n">a.x</span> <span class="bp">+</span> <span class="n">b.x</span> <span class="o">:=</span> <span class="n">rfl</span> </pre></div> </div> <p>It is also possible to define functions on structures using
-
@@ -232,21 +228,21 @@ same; the only difference is that we use anonymous constructor notationin the second. Although it is sometimes convenient to define functions this way, and structural eta-reduction makes this alternative definitionally equivalent, it can make things less convenient in later proofs. In particular, <cite>rw [addAlt]</cite> leaves us with a messier goal view containing a <cite>match</cite> statement.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">addAlt</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Point</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Point</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Point</span> <span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">Point.mk</span><span class="w"> </span><span class="n">x₁</span><span class="w"> </span><span class="n">y₁</span><span class="w"> </span><span class="n">z₁</span><span class="o">,</span><span class="w"> </span><span class="n">Point.mk</span><span class="w"> </span><span class="n">x₂</span><span class="w"> </span><span class="n">y₂</span><span class="w"> </span><span class="n">z₂</span><span class="w"> </span><span class="bp">=></span><span class="w"> </span><span class="o">⟨</span><span class="n">x₁</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">x₂</span><span class="o">,</span><span class="w"> </span><span class="n">y₁</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y₂</span><span class="o">,</span><span class="w"> </span><span class="n">z₁</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">z₂</span><span class="o">⟩</span> In particular, <code class="docutils literal notranslate"><span class="pre">rw</span> <span class="pre">[addAlt]</span></code> leaves us with a messier goal view containing a <code class="docutils literal notranslate"><span class="pre">match</span></code> statement.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">addAlt</span> <span class="o">:</span> <span class="n">Point</span> <span class="bp">→</span> <span class="n">Point</span> <span class="bp">→</span> <span class="n">Point</span> <span class="bp">|</span> <span class="n">Point.mk</span> <span class="n">x₁</span> <span class="n">y₁</span> <span class="n">z₁</span><span class="o">,</span> <span class="n">Point.mk</span> <span class="n">x₂</span> <span class="n">y₂</span> <span class="n">z₂</span> <span class="bp">=></span> <span class="o">⟨</span><span class="n">x₁</span> <span class="bp">+</span> <span class="n">x₂</span><span class="o">,</span> <span class="n">y₁</span> <span class="bp">+</span> <span class="n">y₂</span><span class="o">,</span> <span class="n">z₁</span> <span class="bp">+</span> <span class="n">z₂</span><span class="o">⟩</span> <span class="kd">def</span><span class="w"> </span><span class="n">addAlt'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Point</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Point</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Point</span> <span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="o">⟨</span><span class="n">x₁</span><span class="o">,</span><span class="w"> </span><span class="n">y₁</span><span class="o">,</span><span class="w"> </span><span class="n">z₁</span><span class="o">⟩,</span><span class="w"> </span><span class="o">⟨</span><span class="n">x₂</span><span class="o">,</span><span class="w"> </span><span class="n">y₂</span><span class="o">,</span><span class="w"> </span><span class="n">z₂</span><span class="o">⟩</span><span class="w"> </span><span class="bp">=></span><span class="w"> </span><span class="o">⟨</span><span class="n">x₁</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">x₂</span><span class="o">,</span><span class="w"> </span><span class="n">y₁</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y₂</span><span class="o">,</span><span class="w"> </span><span class="n">z₁</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">z₂</span><span class="o">⟩</span> <span class="kd">def</span> <span class="n">addAlt'</span> <span class="o">:</span> <span class="n">Point</span> <span class="bp">→</span> <span class="n">Point</span> <span class="bp">→</span> <span class="n">Point</span> <span class="bp">|</span> <span class="o">⟨</span><span class="n">x₁</span><span class="o">,</span> <span class="n">y₁</span><span class="o">,</span> <span class="n">z₁</span><span class="o">⟩,</span> <span class="o">⟨</span><span class="n">x₂</span><span class="o">,</span> <span class="n">y₂</span><span class="o">,</span> <span class="n">z₂</span><span class="o">⟩</span> <span class="bp">=></span> <span class="o">⟨</span><span class="n">x₁</span> <span class="bp">+</span> <span class="n">x₂</span><span class="o">,</span> <span class="n">y₁</span> <span class="bp">+</span> <span class="n">y₂</span><span class="o">,</span> <span class="n">z₁</span> <span class="bp">+</span> <span class="n">z₂</span><span class="o">⟩</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">addAlt_x</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Point</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">a.addAlt</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="bp">.</span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a.x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b.x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">theorem</span> <span class="n">addAlt_x</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">Point</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">a.addAlt</span> <span class="n">b</span><span class="o">)</span><span class="bp">.</span><span class="n">x</span> <span class="bp">=</span> <span class="n">a.x</span> <span class="bp">+</span> <span class="n">b.x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rfl</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">addAlt_comm</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Point</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">addAlt</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">addAlt</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">addAlt</span><span class="o">,</span><span class="w"> </span><span class="n">addAlt</span><span class="o">]</span> <span class="w"> </span><span class="c1">-- the same proof still works, but the goal view here is harder to read</span> <span class="w"> </span><span class="n">ext</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">dsimp</span> <span class="w"> </span><span class="n">repeat'</span><span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">add_comm</span> <span class="kd">theorem</span> <span class="n">addAlt_comm</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">Point</span><span class="o">)</span> <span class="o">:</span> <span class="n">addAlt</span> <span class="n">a</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">addAlt</span> <span class="n">b</span> <span class="n">a</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">addAlt</span><span class="o">,</span> <span class="n">addAlt</span><span class="o">]</span> <span class="c1">-- the same proof still works, but the goal view here is harder to read</span> <span class="n">ext</span> <span class="bp"><;></span> <span class="n">dsimp</span> <span class="n">repeat'</span> <span class="n">apply</span> <span class="n">add_comm</span> </pre></div> </div> <p>Mathematical constructions often involve taking apart bundled information and
-
@@ -256,15 +252,15 @@ of doing this efficiently.As an exercise, try proving that <code class="docutils literal notranslate"><span class="pre">Point.add</span></code> is associative. Then define scalar multiplication for a point and show that it distributes over addition.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">protected</span><span class="w"> </span><span class="kd">theorem</span><span class="w"> </span><span class="n">add_assoc</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Point</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">a.add</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="bp">.</span><span class="n">add</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a.add</span><span class="w"> </span><span class="o">(</span><span class="n">b.add</span><span class="w"> </span><span class="n">c</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">protected</span> <span class="kd">theorem</span> <span class="n">add_assoc</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">Point</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">a.add</span> <span class="n">b</span><span class="o">)</span><span class="bp">.</span><span class="n">add</span> <span class="n">c</span> <span class="bp">=</span> <span class="n">a.add</span> <span class="o">(</span><span class="n">b.add</span> <span class="n">c</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">def</span><span class="w"> </span><span class="n">smul</span><span class="w"> </span><span class="o">(</span><span class="n">r</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Point</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Point</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">def</span> <span class="n">smul</span> <span class="o">(</span><span class="n">r</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">Point</span><span class="o">)</span> <span class="o">:</span> <span class="n">Point</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">smul_distrib</span><span class="w"> </span><span class="o">(</span><span class="n">r</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Point</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="o">(</span><span class="n">smul</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="bp">.</span><span class="n">add</span><span class="w"> </span><span class="o">(</span><span class="n">smul</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">smul</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="o">(</span><span class="n">a.add</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">theorem</span> <span class="n">smul_distrib</span> <span class="o">(</span><span class="n">r</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">Point</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">smul</span> <span class="n">r</span> <span class="n">a</span><span class="o">)</span><span class="bp">.</span><span class="n">add</span> <span class="o">(</span><span class="n">smul</span> <span class="n">r</span> <span class="n">b</span><span class="o">)</span> <span class="bp">=</span> <span class="n">smul</span> <span class="n">r</span> <span class="o">(</span><span class="n">a.add</span> <span class="n">b</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>Using structures is only the first step on the road to
-
@@ -288,44 +284,44 @@ the equilateral triangle in three-space with vertices<span class="math notranslate nohighlight">\((1, 0, 0)\)</span>, <span class="math notranslate nohighlight">\((0, 1, 0)\)</span>, and <span class="math notranslate nohighlight">\((0, 0, 1)\)</span>, together with its interior. We can represent it in Lean as follows:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">structure</span><span class="w"> </span><span class="n">StandardTwoSimplex</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span> <span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span> <span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span> <span class="w"> </span><span class="n">x_nonneg</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">x</span> <span class="w"> </span><span class="n">y_nonneg</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">y</span> <span class="w"> </span><span class="n">z_nonneg</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">z</span> <span class="w"> </span><span class="n">sum_eq</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">structure</span> <span class="n">StandardTwoSimplex</span> <span class="n">where</span> <span class="n">x</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="n">z</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="n">x_nonneg</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp">≤</span> <span class="n">x</span> <span class="n">y_nonneg</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp">≤</span> <span class="n">y</span> <span class="n">z_nonneg</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp">≤</span> <span class="n">z</span> <span class="n">sum_eq</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">y</span> <span class="bp">+</span> <span class="n">z</span> <span class="bp">=</span> <span class="mi">1</span> </pre></div> </div> <p>Notice that the last four fields refer to <code class="docutils literal notranslate"><span class="pre">x</span></code>, <code class="docutils literal notranslate"><span class="pre">y</span></code>, and <code class="docutils literal notranslate"><span class="pre">z</span></code>, that is, the first three fields. We can define a map from the two-simplex to itself that swaps <code class="docutils literal notranslate"><span class="pre">x</span></code> and <code class="docutils literal notranslate"><span class="pre">y</span></code>:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">swapXy</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">StandardTwoSimplex</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">StandardTwoSimplex</span> <span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">a.y</span> <span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">a.x</span> <span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">a.z</span> <span class="w"> </span><span class="n">x_nonneg</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">a.y_nonneg</span> <span class="w"> </span><span class="n">y_nonneg</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">a.x_nonneg</span> <span class="w"> </span><span class="n">z_nonneg</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">a.z_nonneg</span> <span class="w"> </span><span class="n">sum_eq</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">add_comm</span><span class="w"> </span><span class="n">a.y</span><span class="w"> </span><span class="n">a.x</span><span class="o">,</span><span class="w"> </span><span class="n">a.sum_eq</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">swapXy</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">StandardTwoSimplex</span><span class="o">)</span> <span class="o">:</span> <span class="n">StandardTwoSimplex</span> <span class="n">where</span> <span class="n">x</span> <span class="o">:=</span> <span class="n">a.y</span> <span class="n">y</span> <span class="o">:=</span> <span class="n">a.x</span> <span class="n">z</span> <span class="o">:=</span> <span class="n">a.z</span> <span class="n">x_nonneg</span> <span class="o">:=</span> <span class="n">a.y_nonneg</span> <span class="n">y_nonneg</span> <span class="o">:=</span> <span class="n">a.x_nonneg</span> <span class="n">z_nonneg</span> <span class="o">:=</span> <span class="n">a.z_nonneg</span> <span class="n">sum_eq</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">add_comm</span> <span class="n">a.y</span> <span class="n">a.x</span><span class="o">,</span> <span class="n">a.sum_eq</span><span class="o">]</span> </pre></div> </div> <p>More interestingly, we can compute the midpoint of two points on the simplex. We have added the phrase <code class="docutils literal notranslate"><span class="pre">noncomputable</span> <span class="pre">section</span></code> at the beginning of this file in order to use division on the real numbers.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">noncomputable</span><span class="w"> </span><span class="kn">section</span> <span class="kd">def</span><span class="w"> </span><span class="n">midpoint</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">StandardTwoSimplex</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">StandardTwoSimplex</span> <span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">(</span><span class="n">a.x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b.x</span><span class="o">)</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span> <span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">(</span><span class="n">a.y</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b.y</span><span class="o">)</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span> <span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">(</span><span class="n">a.z</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b.z</span><span class="o">)</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span> <span class="w"> </span><span class="n">x_nonneg</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">div_nonneg</span><span class="w"> </span><span class="o">(</span><span class="n">add_nonneg</span><span class="w"> </span><span class="n">a.x_nonneg</span><span class="w"> </span><span class="n">b.x_nonneg</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="kd">by</span><span class="w"> </span><span class="n">norm_num</span><span class="o">)</span> <span class="w"> </span><span class="n">y_nonneg</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">div_nonneg</span><span class="w"> </span><span class="o">(</span><span class="n">add_nonneg</span><span class="w"> </span><span class="n">a.y_nonneg</span><span class="w"> </span><span class="n">b.y_nonneg</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="kd">by</span><span class="w"> </span><span class="n">norm_num</span><span class="o">)</span> <span class="w"> </span><span class="n">z_nonneg</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">div_nonneg</span><span class="w"> </span><span class="o">(</span><span class="n">add_nonneg</span><span class="w"> </span><span class="n">a.z_nonneg</span><span class="w"> </span><span class="n">b.z_nonneg</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="kd">by</span><span class="w"> </span><span class="n">norm_num</span><span class="o">)</span> <span class="w"> </span><span class="n">sum_eq</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">field_simp</span><span class="bp">;</span><span class="w"> </span><span class="n">linarith</span><span class="w"> </span><span class="o">[</span><span class="n">a.sum_eq</span><span class="o">,</span><span class="w"> </span><span class="n">b.sum_eq</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">noncomputable</span> <span class="kn">section</span> <span class="kd">def</span> <span class="n">midpoint</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">StandardTwoSimplex</span><span class="o">)</span> <span class="o">:</span> <span class="n">StandardTwoSimplex</span> <span class="n">where</span> <span class="n">x</span> <span class="o">:=</span> <span class="o">(</span><span class="n">a.x</span> <span class="bp">+</span> <span class="n">b.x</span><span class="o">)</span> <span class="bp">/</span> <span class="mi">2</span> <span class="n">y</span> <span class="o">:=</span> <span class="o">(</span><span class="n">a.y</span> <span class="bp">+</span> <span class="n">b.y</span><span class="o">)</span> <span class="bp">/</span> <span class="mi">2</span> <span class="n">z</span> <span class="o">:=</span> <span class="o">(</span><span class="n">a.z</span> <span class="bp">+</span> <span class="n">b.z</span><span class="o">)</span> <span class="bp">/</span> <span class="mi">2</span> <span class="n">x_nonneg</span> <span class="o">:=</span> <span class="n">div_nonneg</span> <span class="o">(</span><span class="n">add_nonneg</span> <span class="n">a.x_nonneg</span> <span class="n">b.x_nonneg</span><span class="o">)</span> <span class="o">(</span><span class="kd">by</span> <span class="n">norm_num</span><span class="o">)</span> <span class="n">y_nonneg</span> <span class="o">:=</span> <span class="n">div_nonneg</span> <span class="o">(</span><span class="n">add_nonneg</span> <span class="n">a.y_nonneg</span> <span class="n">b.y_nonneg</span><span class="o">)</span> <span class="o">(</span><span class="kd">by</span> <span class="n">norm_num</span><span class="o">)</span> <span class="n">z_nonneg</span> <span class="o">:=</span> <span class="n">div_nonneg</span> <span class="o">(</span><span class="n">add_nonneg</span> <span class="n">a.z_nonneg</span> <span class="n">b.z_nonneg</span><span class="o">)</span> <span class="o">(</span><span class="kd">by</span> <span class="n">norm_num</span><span class="o">)</span> <span class="n">sum_eq</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">field_simp</span><span class="bp">;</span> <span class="n">linarith</span> <span class="o">[</span><span class="n">a.sum_eq</span><span class="o">,</span> <span class="n">b.sum_eq</span><span class="o">]</span> </pre></div> </div> <p>Here we have established <code class="docutils literal notranslate"><span class="pre">x_nonneg</span></code>, <code class="docutils literal notranslate"><span class="pre">y_nonneg</span></code>, and <code class="docutils literal notranslate"><span class="pre">z_nonneg</span></code>
-
@@ -336,9 +332,9 @@ we can take the weighted average <span class="math notranslate nohighlight">\(\lof two points <span class="math notranslate nohighlight">\(a\)</span> and <span class="math notranslate nohighlight">\(b\)</span> in the standard 2-simplex. We challenge you to define that function, in analogy to the <code class="docutils literal notranslate"><span class="pre">midpoint</span></code> function above.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">weightedAverage</span><span class="w"> </span><span class="o">(</span><span class="n">lambda</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Real</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">lambda_nonneg</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">lambda</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">lambda_le</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">lambda</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span> <span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">StandardTwoSimplex</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">StandardTwoSimplex</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">weightedAverage</span> <span class="o">(</span><span class="n">lambda</span> <span class="o">:</span> <span class="n">Real</span><span class="o">)</span> <span class="o">(</span><span class="n">lambda_nonneg</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp">≤</span> <span class="n">lambda</span><span class="o">)</span> <span class="o">(</span><span class="n">lambda_le</span> <span class="o">:</span> <span class="n">lambda</span> <span class="bp">≤</span> <span class="mi">1</span><span class="o">)</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">StandardTwoSimplex</span><span class="o">)</span> <span class="o">:</span> <span class="n">StandardTwoSimplex</span> <span class="o">:=</span> <span class="gr">sorry</span> </pre></div> </div> <p>Structures can depend on parameters.
-
@@ -347,29 +343,29 @@ For example, we can generalize the standard 2-simplex to the standardAt this stage, you don’t have to know anything about the type <code class="docutils literal notranslate"><span class="pre">Fin</span> <span class="pre">n</span></code> except that it has <span class="math notranslate nohighlight">\(n\)</span> elements, and that Lean knows how to sum over it.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span><span class="w"> </span><span class="n">BigOperators</span> <span class="kd">structure</span><span class="w"> </span><span class="n">StandardSimplex</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Fin</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span> <span class="w"> </span><span class="n">NonNeg</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Fin</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="n">i</span> <span class="w"> </span><span class="n">sum_eq_one</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="bp">∑</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span> <span class="kn">namespace</span><span class="w"> </span><span class="n">StandardSimplex</span> <span class="kd">def</span><span class="w"> </span><span class="n">midpoint</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">StandardSimplex</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">StandardSimplex</span><span class="w"> </span><span class="n">n</span> <span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">(</span><span class="n">a.V</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b.V</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span> <span class="w"> </span><span class="n">NonNeg</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">i</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">div_nonneg</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">linarith</span><span class="w"> </span><span class="o">[</span><span class="n">a.NonNeg</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">b.NonNeg</span><span class="w"> </span><span class="n">i</span><span class="o">]</span> <span class="w"> </span><span class="n">norm_num</span> <span class="w"> </span><span class="n">sum_eq_one</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="o">[</span><span class="n">div_eq_mul_inv</span><span class="o">,</span><span class="w"> </span><span class="bp">←</span><span class="w"> </span><span class="n">Finset.sum_mul</span><span class="o">,</span><span class="w"> </span><span class="n">Finset.sum_add_distrib</span><span class="o">,</span> <span class="w"> </span><span class="n">a.sum_eq_one</span><span class="o">,</span><span class="w"> </span><span class="n">b.sum_eq_one</span><span class="o">]</span> <span class="w"> </span><span class="n">field_simp</span> <span class="kd">end</span><span class="w"> </span><span class="n">StandardSimplex</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span> <span class="n">BigOperators</span> <span class="kd">structure</span> <span class="n">StandardSimplex</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="n">where</span> <span class="n">V</span> <span class="o">:</span> <span class="n">Fin</span> <span class="n">n</span> <span class="bp">→</span> <span class="n">ℝ</span> <span class="n">NonNeg</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">i</span> <span class="o">:</span> <span class="n">Fin</span> <span class="n">n</span><span class="o">,</span> <span class="mi">0</span> <span class="bp">≤</span> <span class="n">V</span> <span class="n">i</span> <span class="n">sum_eq_one</span> <span class="o">:</span> <span class="o">(</span><span class="bp">∑</span> <span class="n">i</span><span class="o">,</span> <span class="n">V</span> <span class="n">i</span><span class="o">)</span> <span class="bp">=</span> <span class="mi">1</span> <span class="kn">namespace</span> <span class="n">StandardSimplex</span> <span class="kd">def</span> <span class="n">midpoint</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">StandardSimplex</span> <span class="n">n</span><span class="o">)</span> <span class="o">:</span> <span class="n">StandardSimplex</span> <span class="n">n</span> <span class="n">where</span> <span class="n">V</span> <span class="n">i</span> <span class="o">:=</span> <span class="o">(</span><span class="n">a.V</span> <span class="n">i</span> <span class="bp">+</span> <span class="n">b.V</span> <span class="n">i</span><span class="o">)</span> <span class="bp">/</span> <span class="mi">2</span> <span class="n">NonNeg</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">i</span> <span class="n">apply</span> <span class="n">div_nonneg</span> <span class="bp">·</span> <span class="n">linarith</span> <span class="o">[</span><span class="n">a.NonNeg</span> <span class="n">i</span><span class="o">,</span> <span class="n">b.NonNeg</span> <span class="n">i</span><span class="o">]</span> <span class="n">norm_num</span> <span class="n">sum_eq_one</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> <span class="o">[</span><span class="n">div_eq_mul_inv</span><span class="o">,</span> <span class="bp">←</span> <span class="n">Finset.sum_mul</span><span class="o">,</span> <span class="n">Finset.sum_add_distrib</span><span class="o">,</span> <span class="n">a.sum_eq_one</span><span class="o">,</span> <span class="n">b.sum_eq_one</span><span class="o">]</span> <span class="n">field_simp</span> <span class="kd">end</span> <span class="n">StandardSimplex</span> </pre></div> </div> <p>As an exercise, see if you can define the weighted average of
-
@@ -382,15 +378,15 @@ Interestingly, they can also be used to bundle together propertieswithout the data. For example, the next structure, <code class="docutils literal notranslate"><span class="pre">IsLinear</span></code>, bundles together the two components of linearity.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">structure</span><span class="w"> </span><span class="n">IsLinear</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">is_additive</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">y</span> <span class="w"> </span><span class="n">preserves_mul</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">c</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">c</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">structure</span> <span class="n">IsLinear</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">)</span> <span class="n">where</span> <span class="n">is_additive</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span> <span class="n">y</span><span class="o">,</span> <span class="n">f</span> <span class="o">(</span><span class="n">x</span> <span class="bp">+</span> <span class="n">y</span><span class="o">)</span> <span class="bp">=</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">f</span> <span class="n">y</span> <span class="n">preserves_mul</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span> <span class="n">c</span><span class="o">,</span> <span class="n">f</span> <span class="o">(</span><span class="n">c</span> <span class="bp">*</span> <span class="n">x</span><span class="o">)</span> <span class="bp">=</span> <span class="n">c</span> <span class="bp">*</span> <span class="n">f</span> <span class="n">x</span> <span class="kn">section</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">linf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">IsLinear</span><span class="w"> </span><span class="n">f</span><span class="o">)</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">linf</span> <span class="o">:</span> <span class="n">IsLinear</span> <span class="n">f</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="n">linf.is_additive</span> <span class="k">#check</span><span class="w"> </span><span class="n">linf.preserves_mul</span> <span class="k">#check</span> <span class="n">linf.is_additive</span> <span class="k">#check</span> <span class="n">linf.preserves_mul</span> <span class="kd">end</span> </pre></div>
-
@@ -399,11 +395,11 @@ the two components of linearity.</p>together data. The <code class="docutils literal notranslate"><span class="pre">Point</span></code> data structure can be defined using the generic type product, and <code class="docutils literal notranslate"><span class="pre">IsLinear</span></code> can be defined with a simple <code class="docutils literal notranslate"><span class="pre">and</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">Point''</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">×</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">×</span><span class="w"> </span><span class="n">ℝ</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">Point''</span> <span class="o">:=</span> <span class="n">ℝ</span> <span class="bp">×</span> <span class="n">ℝ</span> <span class="bp">×</span> <span class="n">ℝ</span> <span class="kd">def</span><span class="w"> </span><span class="n">IsLinear'</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">(</span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">c</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">c</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span> <span class="kd">def</span> <span class="n">IsLinear'</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:=</span> <span class="o">(</span><span class="bp">∀</span> <span class="n">x</span> <span class="n">y</span><span class="o">,</span> <span class="n">f</span> <span class="o">(</span><span class="n">x</span> <span class="bp">+</span> <span class="n">y</span><span class="o">)</span> <span class="bp">=</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">f</span> <span class="n">y</span><span class="o">)</span> <span class="bp">∧</span> <span class="bp">∀</span> <span class="n">x</span> <span class="n">c</span><span class="o">,</span> <span class="n">f</span> <span class="o">(</span><span class="n">c</span> <span class="bp">*</span> <span class="n">x</span><span class="o">)</span> <span class="bp">=</span> <span class="n">c</span> <span class="bp">*</span> <span class="n">f</span> <span class="n">x</span> </pre></div> </div> <p>Generic type constructions can even be used in place of structures
-
@@ -416,42 +412,42 @@ Any <code class="docutils literal notranslate"><span class="pre">x</span> <spanpositive. You can access these components as <code class="docutils literal notranslate"><span class="pre">x.val</span></code>, which has type <code class="docutils literal notranslate"><span class="pre">ℝ</span></code>, and <code class="docutils literal notranslate"><span class="pre">x.property</span></code>, which represents the fact <code class="docutils literal notranslate"><span class="pre">0</span> <span class="pre"><</span> <span class="pre">x.val</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">PReal</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">//</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">}</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">PReal</span> <span class="o">:=</span> <span class="o">{</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">//</span> <span class="mi">0</span> <span class="bp"><</span> <span class="n">y</span> <span class="o">}</span> <span class="kn">section</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">PReal</span><span class="o">)</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">PReal</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="n">x.val</span> <span class="k">#check</span><span class="w"> </span><span class="n">x.property</span> <span class="k">#check</span><span class="w"> </span><span class="n">x</span><span class="bp">.</span><span class="mi">1</span> <span class="k">#check</span><span class="w"> </span><span class="n">x</span><span class="bp">.</span><span class="mi">2</span> <span class="k">#check</span> <span class="n">x.val</span> <span class="k">#check</span> <span class="n">x.property</span> <span class="k">#check</span> <span class="n">x.1</span> <span class="k">#check</span> <span class="n">x.2</span> <span class="kd">end</span> </pre></div> </div> <p>We could have used subtypes to define the standard 2-simplex, as well as the standard <span class="math notranslate nohighlight">\(n\)</span>-simplex for an arbitrary <span class="math notranslate nohighlight">\(n\)</span>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">StandardTwoSimplex'</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">×</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">×</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">//</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">p</span><span class="bp">.</span><span class="mi">1</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">p</span><span class="bp">.</span><span class="mi">2</span><span class="bp">.</span><span class="mi">1</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">p</span><span class="bp">.</span><span class="mi">2</span><span class="bp">.</span><span class="mi">2</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">p</span><span class="bp">.</span><span class="mi">1</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">p</span><span class="bp">.</span><span class="mi">2</span><span class="bp">.</span><span class="mi">1</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">p</span><span class="bp">.</span><span class="mi">2</span><span class="bp">.</span><span class="mi">2</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">}</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">StandardTwoSimplex'</span> <span class="o">:=</span> <span class="o">{</span> <span class="n">p</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">×</span> <span class="n">ℝ</span> <span class="bp">×</span> <span class="n">ℝ</span> <span class="bp">//</span> <span class="mi">0</span> <span class="bp">≤</span> <span class="n">p.1</span> <span class="bp">∧</span> <span class="mi">0</span> <span class="bp">≤</span> <span class="n">p.2.1</span> <span class="bp">∧</span> <span class="mi">0</span> <span class="bp">≤</span> <span class="n">p.2.2</span> <span class="bp">∧</span> <span class="n">p.1</span> <span class="bp">+</span> <span class="n">p.2.1</span> <span class="bp">+</span> <span class="n">p.2.2</span> <span class="bp">=</span> <span class="mi">1</span> <span class="o">}</span> <span class="kd">def</span><span class="w"> </span><span class="n">StandardSimplex'</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Fin</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">//</span><span class="w"> </span><span class="o">(</span><span class="bp">∀</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Fin</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="o">(</span><span class="bp">∑</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">}</span> <span class="kd">def</span> <span class="n">StandardSimplex'</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">:=</span> <span class="o">{</span> <span class="n">v</span> <span class="o">:</span> <span class="n">Fin</span> <span class="n">n</span> <span class="bp">→</span> <span class="n">ℝ</span> <span class="bp">//</span> <span class="o">(</span><span class="bp">∀</span> <span class="n">i</span> <span class="o">:</span> <span class="n">Fin</span> <span class="n">n</span><span class="o">,</span> <span class="mi">0</span> <span class="bp">≤</span> <span class="n">v</span> <span class="n">i</span><span class="o">)</span> <span class="bp">∧</span> <span class="o">(</span><span class="bp">∑</span> <span class="n">i</span><span class="o">,</span> <span class="n">v</span> <span class="n">i</span><span class="o">)</span> <span class="bp">=</span> <span class="mi">1</span> <span class="o">}</span> </pre></div> </div> <p>Similarly, <em>Sigma types</em> are generalizations of ordered pairs, whereby the type of the second component depends on the type of the first.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">StdSimplex</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="bp">Σ</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">,</span><span class="w"> </span><span class="n">StandardSimplex</span><span class="w"> </span><span class="n">n</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">StdSimplex</span> <span class="o">:=</span> <span class="bp">Σ</span> <span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">,</span> <span class="n">StandardSimplex</span> <span class="n">n</span> <span class="kn">section</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">StdSimplex</span><span class="o">)</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">s</span> <span class="o">:</span> <span class="n">StdSimplex</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="n">s.fst</span> <span class="k">#check</span><span class="w"> </span><span class="n">s.snd</span> <span class="k">#check</span> <span class="n">s.fst</span> <span class="k">#check</span> <span class="n">s.snd</span> <span class="k">#check</span><span class="w"> </span><span class="n">s</span><span class="bp">.</span><span class="mi">1</span> <span class="k">#check</span><span class="w"> </span><span class="n">s</span><span class="bp">.</span><span class="mi">2</span> <span class="k">#check</span> <span class="n">s.1</span> <span class="k">#check</span> <span class="n">s.2</span> <span class="kd">end</span> </pre></div>
-
@@ -474,7 +470,7 @@ weaving structures together into a rich, interconnected hierarchy,and for managing the interactions between them.</p> </section> <section id="algebraic-structures"> <span id="section-algebraic-structures"></span><h2><span class="section-number">6.2. </span>Algebraic Structures<a class="headerlink" href="#algebraic-structures" title="Link to this heading"></a></h2> <span id="section-algebraic-structures"></span><h2><span class="section-number">6.2. </span>Algebraic Structures<a class="headerlink" href="#algebraic-structures" title="Permalink to this heading"></a></h2> <p>To clarify what we mean by the phrase <em>algebraic structure</em>, it will help to consider some examples.</p> <ol class="arabic simple">
-
@@ -592,17 +588,17 @@ this is exactly what the <code class="docutils literal notranslate"><span class=It’s a marriage made in heaven!</p> <p>Given a data type <code class="docutils literal notranslate"><span class="pre">α</span></code>, we can define the group structure on <code class="docutils literal notranslate"><span class="pre">α</span></code> as follows.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">structure</span><span class="w"> </span><span class="n">Group₁</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">)</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">mul</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">α</span> <span class="w"> </span><span class="n">one</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span> <span class="w"> </span><span class="n">inv</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">α</span> <span class="w"> </span><span class="n">mul_assoc</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">,</span><span class="w"> </span><span class="n">mul</span><span class="w"> </span><span class="o">(</span><span class="n">mul</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">mul</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">(</span><span class="n">mul</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">z</span><span class="o">)</span> <span class="w"> </span><span class="n">mul_one</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">,</span><span class="w"> </span><span class="n">mul</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">one</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x</span> <span class="w"> </span><span class="n">one_mul</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">,</span><span class="w"> </span><span class="n">mul</span><span class="w"> </span><span class="n">one</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x</span> <span class="w"> </span><span class="n">inv_mul_cancel</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">,</span><span class="w"> </span><span class="n">mul</span><span class="w"> </span><span class="o">(</span><span class="n">inv</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">one</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">structure</span> <span class="n">Group₁</span> <span class="o">(</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">)</span> <span class="n">where</span> <span class="n">mul</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">α</span> <span class="n">one</span> <span class="o">:</span> <span class="n">α</span> <span class="n">inv</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">α</span> <span class="n">mul_assoc</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span> <span class="n">y</span> <span class="n">z</span> <span class="o">:</span> <span class="n">α</span><span class="o">,</span> <span class="n">mul</span> <span class="o">(</span><span class="n">mul</span> <span class="n">x</span> <span class="n">y</span><span class="o">)</span> <span class="n">z</span> <span class="bp">=</span> <span class="n">mul</span> <span class="n">x</span> <span class="o">(</span><span class="n">mul</span> <span class="n">y</span> <span class="n">z</span><span class="o">)</span> <span class="n">mul_one</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span> <span class="o">:</span> <span class="n">α</span><span class="o">,</span> <span class="n">mul</span> <span class="n">x</span> <span class="n">one</span> <span class="bp">=</span> <span class="n">x</span> <span class="n">one_mul</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span> <span class="o">:</span> <span class="n">α</span><span class="o">,</span> <span class="n">mul</span> <span class="n">one</span> <span class="n">x</span> <span class="bp">=</span> <span class="n">x</span> <span class="n">inv_mul_cancel</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span> <span class="o">:</span> <span class="n">α</span><span class="o">,</span> <span class="n">mul</span> <span class="o">(</span><span class="n">inv</span> <span class="n">x</span><span class="o">)</span> <span class="n">x</span> <span class="bp">=</span> <span class="n">one</span> </pre></div> </div> <p>Notice that the type <code class="docutils literal notranslate"><span class="pre">α</span></code> is a <em>parameter</em> in the definition of <code class="docutils literal notranslate"><span class="pre">group₁</span></code>. <p>Notice that the type <code class="docutils literal notranslate"><span class="pre">α</span></code> is a <em>parameter</em> in the definition of <code class="docutils literal notranslate"><span class="pre">Group₁</span></code>. So you should think of an object <code class="docutils literal notranslate"><span class="pre">struc</span> <span class="pre">:</span> <span class="pre">Group₁</span> <span class="pre">α</span></code> as being a group structure on <code class="docutils literal notranslate"><span class="pre">α</span></code>. We saw in <a class="reference internal" href="C02_Basics.html#proving-identities-in-algebraic-structures"><span class="std std-numref">Section 2.2</span></a>
-
@@ -628,9 +624,9 @@ morally the same as the definition of a group that Mathlib uses.</p>the type together with the structure, and Mathlib also contains a definition of a <code class="docutils literal notranslate"><span class="pre">GroupCat</span></code> structure that is equivalent to the following:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">structure</span><span class="w"> </span><span class="n">Group₁Cat</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span> <span class="w"> </span><span class="n">str</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Group₁</span><span class="w"> </span><span class="n">α</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">structure</span> <span class="n">Group₁Cat</span> <span class="n">where</span> <span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span> <span class="n">str</span> <span class="o">:</span> <span class="n">Group₁</span> <span class="n">α</span> </pre></div> </div> <p>The Mathlib version is found in <code class="docutils literal notranslate"><span class="pre">Mathlib.Algebra.Category.GroupCat.Basic</span></code>,
-
@@ -653,17 +649,17 @@ a function <code class="docutils literal notranslate"><span class="pre">f.toFun<the inverse function <code class="docutils literal notranslate"><span class="pre">f.invFun</span></code> from <code class="docutils literal notranslate"><span class="pre">β</span></code> to <code class="docutils literal notranslate"><span class="pre">α</span></code>, and two properties that specify these functions are indeed inverse to one another.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="n">β</span><span class="w"> </span><span class="n">γ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">)</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">≃</span><span class="w"> </span><span class="n">β</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">g</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">β</span><span class="w"> </span><span class="bp">≃</span><span class="w"> </span><span class="n">γ</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="n">Equiv</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="n">β</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">f.toFun</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">β</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">f.invFun</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">β</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">α</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">f.right_inv</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">β</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">f.invFun</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">f.left_inv</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">,</span><span class="w"> </span><span class="n">f.invFun</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">Equiv.refl</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">≃</span><span class="w"> </span><span class="n">α</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">f.symm</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">β</span><span class="w"> </span><span class="bp">≃</span><span class="w"> </span><span class="n">α</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">f.trans</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">≃</span><span class="w"> </span><span class="n">γ</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">(</span><span class="n">α</span> <span class="n">β</span> <span class="n">γ</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">)</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">≃</span> <span class="n">β</span><span class="o">)</span> <span class="o">(</span><span class="n">g</span> <span class="o">:</span> <span class="n">β</span> <span class="bp">≃</span> <span class="n">γ</span><span class="o">)</span> <span class="k">#check</span> <span class="n">Equiv</span> <span class="n">α</span> <span class="n">β</span> <span class="k">#check</span> <span class="o">(</span><span class="n">f.toFun</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">β</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">f.invFun</span> <span class="o">:</span> <span class="n">β</span> <span class="bp">→</span> <span class="n">α</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">f.right_inv</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span> <span class="o">:</span> <span class="n">β</span><span class="o">,</span> <span class="n">f</span> <span class="o">(</span><span class="n">f.invFun</span> <span class="n">x</span><span class="o">)</span> <span class="bp">=</span> <span class="n">x</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">f.left_inv</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span> <span class="o">:</span> <span class="n">α</span><span class="o">,</span> <span class="n">f.invFun</span> <span class="o">(</span><span class="n">f</span> <span class="n">x</span><span class="o">)</span> <span class="bp">=</span> <span class="n">x</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">Equiv.refl</span> <span class="n">α</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">≃</span> <span class="n">α</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">f.symm</span> <span class="o">:</span> <span class="n">β</span> <span class="bp">≃</span> <span class="n">α</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">f.trans</span> <span class="n">g</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">≃</span> <span class="n">γ</span><span class="o">)</span> </pre></div> </div> <p>Notice the creative naming of the last three constructions. We think of the
-
@@ -674,20 +670,20 @@ that the property of being in bijective correspondence is an equivalence relatioin reverse order. Mathlib has declared a <em>coercion</em> from <code class="docutils literal notranslate"><span class="pre">Equiv</span> <span class="pre">α</span> <span class="pre">β</span></code> to the function type <code class="docutils literal notranslate"><span class="pre">α</span> <span class="pre">→</span> <span class="pre">β</span></code>, so we can omit writing <code class="docutils literal notranslate"><span class="pre">.toFun</span></code> and have Lean insert it for us.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">f.trans</span><span class="w"> </span><span class="n">g</span><span class="o">)</span><span class="bp">.</span><span class="n">toFun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">g.toFun</span><span class="w"> </span><span class="o">(</span><span class="n">f.toFun</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">α</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">f.trans</span> <span class="n">g</span><span class="o">)</span><span class="bp">.</span><span class="n">toFun</span> <span class="n">x</span> <span class="bp">=</span> <span class="n">g.toFun</span> <span class="o">(</span><span class="n">f.toFun</span> <span class="n">x</span><span class="o">)</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">f.trans</span><span class="w"> </span><span class="n">g</span><span class="o">)</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">example</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">α</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">f.trans</span> <span class="n">g</span><span class="o">)</span> <span class="n">x</span> <span class="bp">=</span> <span class="n">g</span> <span class="o">(</span><span class="n">f</span> <span class="n">x</span><span class="o">)</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">f.trans</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">γ</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="bp">∘</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">example</span> <span class="o">:</span> <span class="o">(</span><span class="n">f.trans</span> <span class="n">g</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">γ</span><span class="o">)</span> <span class="bp">=</span> <span class="n">g</span> <span class="bp">∘</span> <span class="n">f</span> <span class="o">:=</span> <span class="n">rfl</span> </pre></div> </div> <p>Mathlib also defines the type <code class="docutils literal notranslate"><span class="pre">perm</span> <span class="pre">α</span></code> of equivalences between <code class="docutils literal notranslate"><span class="pre">α</span></code> and itself.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Equiv.Perm</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="bp">≃</span><span class="w"> </span><span class="n">α</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">)</span> <span class="o">:</span> <span class="n">Equiv.Perm</span> <span class="n">α</span> <span class="bp">=</span> <span class="o">(</span><span class="n">α</span> <span class="bp">≃</span> <span class="n">α</span><span class="o">)</span> <span class="o">:=</span> <span class="n">rfl</span> </pre></div> </div> <p>It should be clear that <code class="docutils literal notranslate"><span class="pre">Equiv.Perm</span> <span class="pre">α</span></code> forms a group under composition
-
@@ -695,15 +691,15 @@ of equivalences. We orient things so that <code class="docutils literal notranslequal to <code class="docutils literal notranslate"><span class="pre">g.trans</span> <span class="pre">f</span></code>, whose forward function is <code class="docutils literal notranslate"><span class="pre">f</span> <span class="pre">∘</span> <span class="pre">g</span></code>. In other words, multiplication is what we ordinarily think of as composition of the bijections. Here we define this group:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">permGroup</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Group₁</span><span class="w"> </span><span class="o">(</span><span class="n">Equiv.Perm</span><span class="w"> </span><span class="n">α</span><span class="o">)</span> <span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">mul</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Equiv.trans</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">f</span> <span class="w"> </span><span class="n">one</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Equiv.refl</span><span class="w"> </span><span class="n">α</span> <span class="w"> </span><span class="n">inv</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Equiv.symm</span> <span class="w"> </span><span class="n">mul_assoc</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">(</span><span class="n">Equiv.trans_assoc</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="n">_</span><span class="o">)</span><span class="bp">.</span><span class="n">symm</span> <span class="w"> </span><span class="n">one_mul</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Equiv.trans_refl</span> <span class="w"> </span><span class="n">mul_one</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Equiv.refl_trans</span> <span class="w"> </span><span class="n">inv_mul_cancel</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Equiv.self_trans_symm</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">permGroup</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">:</span> <span class="n">Group₁</span> <span class="o">(</span><span class="n">Equiv.Perm</span> <span class="n">α</span><span class="o">)</span> <span class="n">where</span> <span class="n">mul</span> <span class="n">f</span> <span class="n">g</span> <span class="o">:=</span> <span class="n">Equiv.trans</span> <span class="n">g</span> <span class="n">f</span> <span class="n">one</span> <span class="o">:=</span> <span class="n">Equiv.refl</span> <span class="n">α</span> <span class="n">inv</span> <span class="o">:=</span> <span class="n">Equiv.symm</span> <span class="n">mul_assoc</span> <span class="n">f</span> <span class="n">g</span> <span class="n">h</span> <span class="o">:=</span> <span class="o">(</span><span class="n">Equiv.trans_assoc</span> <span class="n">_</span> <span class="n">_</span> <span class="n">_</span><span class="o">)</span><span class="bp">.</span><span class="n">symm</span> <span class="n">one_mul</span> <span class="o">:=</span> <span class="n">Equiv.trans_refl</span> <span class="n">mul_one</span> <span class="o">:=</span> <span class="n">Equiv.refl_trans</span> <span class="n">inv_mul_cancel</span> <span class="o">:=</span> <span class="n">Equiv.self_trans_symm</span> </pre></div> </div> <p>In fact, Mathlib defines exactly this <code class="docutils literal notranslate"><span class="pre">Group</span></code> structure on <code class="docutils literal notranslate"><span class="pre">Equiv.Perm</span> <span class="pre">α</span></code>
-
@@ -717,7 +713,7 @@ independent of structure.For example, we can consider groups <span class="math notranslate nohighlight">\((G_1, \cdot, 1, \cdot^{-1})\)</span>, <span class="math notranslate nohighlight">\((G_2, \circ, e, i(\cdot))\)</span>, and <span class="math notranslate nohighlight">\((G_3, +, 0, -)\)</span>. In the first case, we write the binary operation as <span class="math notranslate nohighlight">\(\cdot\)</span>, the identity at <span class="math notranslate nohighlight">\(1\)</span>, and the inverse function as <span class="math notranslate nohighlight">\(x \mapsto x^{-1}\)</span>. the identity as <span class="math notranslate nohighlight">\(1\)</span>, and the inverse function as <span class="math notranslate nohighlight">\(x \mapsto x^{-1}\)</span>. In the second and third cases, we use the notational alternatives shown. When we formalize the notion of a group in Lean, however, the notation is more tightly linked to the structure.
-
@@ -737,27 +733,27 @@ to the <code class="docutils literal notranslate"><span class="pre">Group₁additive naming scheme just described. Define negation and a zero on the <code class="docutils literal notranslate"><span class="pre">Point</span></code> data type, and define the <code class="docutils literal notranslate"><span class="pre">AddGroup₁</span></code> structure on <code class="docutils literal notranslate"><span class="pre">Point</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">structure</span><span class="w"> </span><span class="n">AddGroup₁</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">)</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="o">(</span><span class="n">add</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">α</span><span class="o">)</span> <span class="w"> </span><span class="c1">-- fill in the rest</span> <span class="kd">@[</span><span class="n">ext</span><span class="kd">]</span> <span class="kd">structure</span><span class="w"> </span><span class="n">Point</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span> <span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span> <span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">structure</span> <span class="n">AddGroup₁</span> <span class="o">(</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">)</span> <span class="n">where</span> <span class="o">(</span><span class="n">add</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">α</span><span class="o">)</span> <span class="c1">-- fill in the rest</span> <span class="kd">@[ext]</span> <span class="kd">structure</span> <span class="n">Point</span> <span class="n">where</span> <span class="n">x</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="n">z</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="kn">namespace</span><span class="w"> </span><span class="n">Point</span> <span class="kn">namespace</span> <span class="n">Point</span> <span class="kd">def</span><span class="w"> </span><span class="n">add</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Point</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Point</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">⟨</span><span class="n">a.x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b.x</span><span class="o">,</span><span class="w"> </span><span class="n">a.y</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b.y</span><span class="o">,</span><span class="w"> </span><span class="n">a.z</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b.z</span><span class="o">⟩</span> <span class="kd">def</span> <span class="n">add</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">Point</span><span class="o">)</span> <span class="o">:</span> <span class="n">Point</span> <span class="o">:=</span> <span class="o">⟨</span><span class="n">a.x</span> <span class="bp">+</span> <span class="n">b.x</span><span class="o">,</span> <span class="n">a.y</span> <span class="bp">+</span> <span class="n">b.y</span><span class="o">,</span> <span class="n">a.z</span> <span class="bp">+</span> <span class="n">b.z</span><span class="o">⟩</span> <span class="kd">def</span><span class="w"> </span><span class="n">neg</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Point</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Point</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <span class="kd">def</span> <span class="n">neg</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">Point</span><span class="o">)</span> <span class="o">:</span> <span class="n">Point</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="kd">def</span><span class="w"> </span><span class="n">zero</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Point</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <span class="kd">def</span> <span class="n">zero</span> <span class="o">:</span> <span class="n">Point</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="kd">def</span><span class="w"> </span><span class="n">addGroupPoint</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">AddGroup₁</span><span class="w"> </span><span class="n">Point</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <span class="kd">def</span> <span class="n">addGroupPoint</span> <span class="o">:</span> <span class="n">AddGroup₁</span> <span class="n">Point</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="kd">end</span><span class="w"> </span><span class="n">Point</span> <span class="kd">end</span> <span class="n">Point</span> </pre></div> </div> <p>We are making progress.
-
@@ -771,21 +767,21 @@ and we want to arrange it so that we can prove a theorem abouta structure and use it with any instance.</p> <p>In fact, Mathlib is already set up to use generic group notation, definitions, and theorems for <code class="docutils literal notranslate"><span class="pre">Equiv.Perm</span> <span class="pre">α</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Equiv.Perm</span><span class="w"> </span><span class="n">α</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">(</span><span class="n">f</span> <span class="n">g</span> <span class="o">:</span> <span class="n">Equiv.Perm</span> <span class="n">α</span><span class="o">)</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">g</span> <span class="k">#check</span><span class="w"> </span><span class="n">mul_assoc</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">g</span><span class="bp">⁻¹</span> <span class="k">#check</span> <span class="n">f</span> <span class="bp">*</span> <span class="n">g</span> <span class="k">#check</span> <span class="n">mul_assoc</span> <span class="n">f</span> <span class="n">g</span> <span class="n">g</span><span class="bp">⁻¹</span> <span class="c1">-- group power, defined for any group</span> <span class="k">#check</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="n">n</span> <span class="k">#check</span> <span class="n">g</span> <span class="bp">^</span> <span class="n">n</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">g</span><span class="bp">⁻¹</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">mul_assoc</span><span class="o">,</span><span class="w"> </span><span class="n">mul_inv_cancel</span><span class="o">,</span><span class="w"> </span><span class="n">mul_one</span><span class="o">]</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">f</span> <span class="bp">*</span> <span class="n">g</span> <span class="bp">*</span> <span class="n">g</span><span class="bp">⁻¹</span> <span class="bp">=</span> <span class="n">f</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">mul_assoc</span><span class="o">,</span> <span class="n">mul_inv_cancel</span><span class="o">,</span> <span class="n">mul_one</span><span class="o">]</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">g</span><span class="bp">⁻¹</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">mul_inv_cancel_right</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">f</span> <span class="bp">*</span> <span class="n">g</span> <span class="bp">*</span> <span class="n">g</span><span class="bp">⁻¹</span> <span class="bp">=</span> <span class="n">f</span> <span class="o">:=</span> <span class="n">mul_inv_cancel_right</span> <span class="n">f</span> <span class="n">g</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Equiv.Perm</span><span class="w"> </span><span class="n">α</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">g.symm.trans</span><span class="w"> </span><span class="o">(</span><span class="n">g.trans</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">mul_inv_cancel_right</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g</span> <span class="kd">example</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">(</span><span class="n">f</span> <span class="n">g</span> <span class="o">:</span> <span class="n">Equiv.Perm</span> <span class="n">α</span><span class="o">)</span> <span class="o">:</span> <span class="n">g.symm.trans</span> <span class="o">(</span><span class="n">g.trans</span> <span class="n">f</span><span class="o">)</span> <span class="bp">=</span> <span class="n">f</span> <span class="o">:=</span> <span class="n">mul_inv_cancel_right</span> <span class="n">f</span> <span class="n">g</span> </pre></div> </div> <p>You can check that this is not the case for the additive group structure
-
@@ -849,41 +845,41 @@ Lean. As with the names of class variables, we are allowed to leave thename of an instance definition anonymous, since in general we intend Lean to find it and put it to use without troubling us with the details.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span><span class="w"> </span><span class="n">Group₂</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">)</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">mul</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">α</span> <span class="w"> </span><span class="n">one</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span> <span class="w"> </span><span class="n">inv</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">α</span> <span class="w"> </span><span class="n">mul_assoc</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">,</span><span class="w"> </span><span class="n">mul</span><span class="w"> </span><span class="o">(</span><span class="n">mul</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">mul</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">(</span><span class="n">mul</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">z</span><span class="o">)</span> <span class="w"> </span><span class="n">mul_one</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">,</span><span class="w"> </span><span class="n">mul</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">one</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x</span> <span class="w"> </span><span class="n">one_mul</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">,</span><span class="w"> </span><span class="n">mul</span><span class="w"> </span><span class="n">one</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x</span> <span class="w"> </span><span class="n">inv_mul_cancel</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">,</span><span class="w"> </span><span class="n">mul</span><span class="w"> </span><span class="o">(</span><span class="n">inv</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">one</span> <span class="kd">instance</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Group₂</span><span class="w"> </span><span class="o">(</span><span class="n">Equiv.Perm</span><span class="w"> </span><span class="n">α</span><span class="o">)</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">mul</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Equiv.trans</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">f</span> <span class="w"> </span><span class="n">one</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Equiv.refl</span><span class="w"> </span><span class="n">α</span> <span class="w"> </span><span class="n">inv</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Equiv.symm</span> <span class="w"> </span><span class="n">mul_assoc</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">(</span><span class="n">Equiv.trans_assoc</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="n">_</span><span class="o">)</span><span class="bp">.</span><span class="n">symm</span> <span class="w"> </span><span class="n">one_mul</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Equiv.trans_refl</span> <span class="w"> </span><span class="n">mul_one</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Equiv.refl_trans</span> <span class="w"> </span><span class="n">inv_mul_cancel</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Equiv.self_trans_symm</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span> <span class="n">Group₂</span> <span class="o">(</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">)</span> <span class="n">where</span> <span class="n">mul</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">α</span> <span class="n">one</span> <span class="o">:</span> <span class="n">α</span> <span class="n">inv</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">α</span> <span class="n">mul_assoc</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span> <span class="n">y</span> <span class="n">z</span> <span class="o">:</span> <span class="n">α</span><span class="o">,</span> <span class="n">mul</span> <span class="o">(</span><span class="n">mul</span> <span class="n">x</span> <span class="n">y</span><span class="o">)</span> <span class="n">z</span> <span class="bp">=</span> <span class="n">mul</span> <span class="n">x</span> <span class="o">(</span><span class="n">mul</span> <span class="n">y</span> <span class="n">z</span><span class="o">)</span> <span class="n">mul_one</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span> <span class="o">:</span> <span class="n">α</span><span class="o">,</span> <span class="n">mul</span> <span class="n">x</span> <span class="n">one</span> <span class="bp">=</span> <span class="n">x</span> <span class="n">one_mul</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span> <span class="o">:</span> <span class="n">α</span><span class="o">,</span> <span class="n">mul</span> <span class="n">one</span> <span class="n">x</span> <span class="bp">=</span> <span class="n">x</span> <span class="n">inv_mul_cancel</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span> <span class="o">:</span> <span class="n">α</span><span class="o">,</span> <span class="n">mul</span> <span class="o">(</span><span class="n">inv</span> <span class="n">x</span><span class="o">)</span> <span class="n">x</span> <span class="bp">=</span> <span class="n">one</span> <span class="kd">instance</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">:</span> <span class="n">Group₂</span> <span class="o">(</span><span class="n">Equiv.Perm</span> <span class="n">α</span><span class="o">)</span> <span class="n">where</span> <span class="n">mul</span> <span class="n">f</span> <span class="n">g</span> <span class="o">:=</span> <span class="n">Equiv.trans</span> <span class="n">g</span> <span class="n">f</span> <span class="n">one</span> <span class="o">:=</span> <span class="n">Equiv.refl</span> <span class="n">α</span> <span class="n">inv</span> <span class="o">:=</span> <span class="n">Equiv.symm</span> <span class="n">mul_assoc</span> <span class="n">f</span> <span class="n">g</span> <span class="n">h</span> <span class="o">:=</span> <span class="o">(</span><span class="n">Equiv.trans_assoc</span> <span class="n">_</span> <span class="n">_</span> <span class="n">_</span><span class="o">)</span><span class="bp">.</span><span class="n">symm</span> <span class="n">one_mul</span> <span class="o">:=</span> <span class="n">Equiv.trans_refl</span> <span class="n">mul_one</span> <span class="o">:=</span> <span class="n">Equiv.refl_trans</span> <span class="n">inv_mul_cancel</span> <span class="o">:=</span> <span class="n">Equiv.self_trans_symm</span> </pre></div> </div> <p>The following illustrates their use.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="n">Group₂.mul</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="n">Group₂.mul</span> <span class="kd">def</span><span class="w"> </span><span class="n">mySquare</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group₂</span><span class="w"> </span><span class="n">α</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Group₂.mul</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">x</span> <span class="kd">def</span> <span class="n">mySquare</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group₂</span> <span class="n">α</span><span class="o">]</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">α</span><span class="o">)</span> <span class="o">:=</span> <span class="n">Group₂.mul</span> <span class="n">x</span> <span class="n">x</span> <span class="k">#check</span><span class="w"> </span><span class="n">mySquare</span> <span class="k">#check</span> <span class="n">mySquare</span> <span class="kn">section</span> <span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">β</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Equiv.Perm</span><span class="w"> </span><span class="n">β</span><span class="o">)</span> <span class="kd">variable</span> <span class="o">{</span><span class="n">β</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">(</span><span class="n">f</span> <span class="n">g</span> <span class="o">:</span> <span class="n">Equiv.Perm</span> <span class="n">β</span><span class="o">)</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Group₂.mul</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">g.trans</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">Group₂.mul</span> <span class="n">f</span> <span class="n">g</span> <span class="bp">=</span> <span class="n">g.trans</span> <span class="n">f</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">mySquare</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">f.trans</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">mySquare</span> <span class="n">f</span> <span class="bp">=</span> <span class="n">f.trans</span> <span class="n">f</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="kd">end</span> </pre></div>
-
@@ -916,12 +912,12 @@ element of a list, can return the default value when the list is empty.To make that work, the Lean library defines a class <code class="docutils literal notranslate"><span class="pre">Inhabited</span> <span class="pre">α</span></code>, which does nothing more than store a default value. We can show that the <code class="docutils literal notranslate"><span class="pre">Point</span></code> type is an instance:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Inhabited</span><span class="w"> </span><span class="n">Point</span><span class="w"> </span><span class="n">where</span><span class="w"> </span><span class="n">default</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">⟨</span><span class="mi">0</span><span class="o">,</span><span class="w"> </span><span class="mi">0</span><span class="o">,</span><span class="w"> </span><span class="mi">0</span><span class="o">⟩</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span> <span class="o">:</span> <span class="n">Inhabited</span> <span class="n">Point</span> <span class="n">where</span> <span class="n">default</span> <span class="o">:=</span> <span class="o">⟨</span><span class="mi">0</span><span class="o">,</span> <span class="mi">0</span><span class="o">,</span> <span class="mi">0</span><span class="o">⟩</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">default</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Point</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">default</span> <span class="o">:</span> <span class="n">Point</span><span class="o">)</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">([]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">List</span><span class="w"> </span><span class="n">Point</span><span class="o">)</span><span class="bp">.</span><span class="n">headI</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">default</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">example</span> <span class="o">:</span> <span class="o">([]</span> <span class="o">:</span> <span class="n">List</span> <span class="n">Point</span><span class="o">)</span><span class="bp">.</span><span class="n">headI</span> <span class="bp">=</span> <span class="n">default</span> <span class="o">:=</span> <span class="n">rfl</span> </pre></div> </div> <p>The class inference mechanism is also used for generic notation.
-
@@ -931,15 +927,15 @@ a binary function on <code class="docutils literal notranslate"><span class="preWriting <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">+</span> <span class="pre">y</span></code> tells Lean to find a registered instance of <code class="docutils literal notranslate"><span class="pre">[Add.add</span> <span class="pre">α]</span></code> and use the corresponding function. Below, we register the addition function for <code class="docutils literal notranslate"><span class="pre">Point</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Add</span><span class="w"> </span><span class="n">Point</span><span class="w"> </span><span class="n">where</span><span class="w"> </span><span class="n">add</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Point.add</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span> <span class="o">:</span> <span class="n">Add</span> <span class="n">Point</span> <span class="n">where</span> <span class="n">add</span> <span class="o">:=</span> <span class="n">Point.add</span> <span class="kn">section</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Point</span><span class="o">)</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">Point</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y</span> <span class="k">#check</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">y</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">Point.add</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">y</span> <span class="bp">=</span> <span class="n">Point.add</span> <span class="n">x</span> <span class="n">y</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="kd">end</span> </pre></div>
-
@@ -953,22 +949,22 @@ When we define a new instance of a ring in Lean,we don’t have to define <code class="docutils literal notranslate"><span class="pre">+</span></code> and <code class="docutils literal notranslate"><span class="pre">*</span></code> for that instance, because Lean knows that these are defined for every ring. We can use this method to specify notation for our <code class="docutils literal notranslate"><span class="pre">Group₂</span></code> class:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span><span class="w"> </span><span class="n">hasMulGroup₂</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group₂</span><span class="w"> </span><span class="n">α</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Mul</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">⟨</span><span class="n">Group₂.mul</span><span class="o">⟩</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span> <span class="n">hasMulGroup₂</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group₂</span> <span class="n">α</span><span class="o">]</span> <span class="o">:</span> <span class="n">Mul</span> <span class="n">α</span> <span class="o">:=</span> <span class="o">⟨</span><span class="n">Group₂.mul</span><span class="o">⟩</span> <span class="kd">instance</span><span class="w"> </span><span class="n">hasOneGroup₂</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group₂</span><span class="w"> </span><span class="n">α</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">⟨</span><span class="n">Group₂.one</span><span class="o">⟩</span> <span class="kd">instance</span> <span class="n">hasOneGroup₂</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group₂</span> <span class="n">α</span><span class="o">]</span> <span class="o">:</span> <span class="n">One</span> <span class="n">α</span> <span class="o">:=</span> <span class="o">⟨</span><span class="n">Group₂.one</span><span class="o">⟩</span> <span class="kd">instance</span><span class="w"> </span><span class="n">hasInvGroup₂</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group₂</span><span class="w"> </span><span class="n">α</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Inv</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">⟨</span><span class="n">Group₂.inv</span><span class="o">⟩</span> <span class="kd">instance</span> <span class="n">hasInvGroup₂</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group₂</span> <span class="n">α</span><span class="o">]</span> <span class="o">:</span> <span class="n">Inv</span> <span class="n">α</span> <span class="o">:=</span> <span class="o">⟨</span><span class="n">Group₂.inv</span><span class="o">⟩</span> <span class="kn">section</span> <span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Equiv.Perm</span><span class="w"> </span><span class="n">α</span><span class="o">)</span> <span class="kd">variable</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">(</span><span class="n">f</span> <span class="n">g</span> <span class="o">:</span> <span class="n">Equiv.Perm</span> <span class="n">α</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">g</span><span class="bp">⁻¹</span> <span class="k">#check</span> <span class="n">f</span> <span class="bp">*</span> <span class="mi">1</span> <span class="bp">*</span> <span class="n">g</span><span class="bp">⁻¹</span> <span class="kd">def</span><span class="w"> </span><span class="n">foo</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">g</span><span class="bp">⁻¹</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">g.symm.trans</span><span class="w"> </span><span class="o">((</span><span class="n">Equiv.refl</span><span class="w"> </span><span class="n">α</span><span class="o">)</span><span class="bp">.</span><span class="n">trans</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">def</span> <span class="n">foo</span> <span class="o">:</span> <span class="n">f</span> <span class="bp">*</span> <span class="mi">1</span> <span class="bp">*</span> <span class="n">g</span><span class="bp">⁻¹</span> <span class="bp">=</span> <span class="n">g.symm.trans</span> <span class="o">((</span><span class="n">Equiv.refl</span> <span class="n">α</span><span class="o">)</span><span class="bp">.</span><span class="n">trans</span> <span class="n">f</span><span class="o">)</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="kd">end</span> </pre></div>
-
@@ -1007,9 +1003,9 @@ using the classes <code class="docutils literal notranslate"><span class="pre">AThen show <code class="docutils literal notranslate"><span class="pre">Point</span></code> is an instance of <code class="docutils literal notranslate"><span class="pre">AddGroup₂</span></code>. Try it out and make sure that the additive group notation works for elements of <code class="docutils literal notranslate"><span class="pre">Point</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span><span class="w"> </span><span class="n">AddGroup₂</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">)</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">add</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">α</span> <span class="w"> </span><span class="c1">-- fill in the rest</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span> <span class="n">AddGroup₂</span> <span class="o">(</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">)</span> <span class="n">where</span> <span class="n">add</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">α</span> <span class="c1">-- fill in the rest</span> </pre></div> </div> <p>It is not a big problem that we have already declared instances
-
@@ -1023,7 +1019,7 @@ When used wisely, however, class inference is a powerful tool.It is what makes algebraic reasoning possible in Lean.</p> </section> <section id="building-the-gaussian-integers"> <span id="section-building-the-gaussian-integers"></span><h2><span class="section-number">6.3. </span>Building the Gaussian Integers<a class="headerlink" href="#building-the-gaussian-integers" title="Link to this heading"></a></h2> <span id="section-building-the-gaussian-integers"></span><h2><span class="section-number">6.3. </span>Building the Gaussian Integers<a class="headerlink" href="#building-the-gaussian-integers" title="Permalink to this heading"></a></h2> <p>We will now illustrate the use of the algebraic hierarchy in Lean by building an important mathematical object, the <em>Gaussian integers</em>, and showing that it is a Euclidean domain. In other words, according to
-
@@ -1035,10 +1031,10 @@ But rather than define them as a subset of the complex numbers, our goalhere is to define them as a data type in their own right. We do this by representing a Gaussian integer as a pair of integers, which we think of as the <em>real</em> and <em>imaginary</em> parts.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">@[</span><span class="n">ext</span><span class="kd">]</span> <span class="kd">structure</span><span class="w"> </span><span class="n">GaussInt</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">re</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℤ</span> <span class="w"> </span><span class="n">im</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℤ</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">@[ext]</span> <span class="kd">structure</span> <span class="n">GaussInt</span> <span class="n">where</span> <span class="n">re</span> <span class="o">:</span> <span class="n">ℤ</span> <span class="n">im</span> <span class="o">:</span> <span class="n">ℤ</span> </pre></div> </div> <p>We first show that the Gaussian integers have the structure of a ring,
-
@@ -1050,20 +1046,20 @@ be a square root of <span class="math notranslate nohighlight">\(-1\)</span>. Th\[\begin{split}(a + bi) (c + di) & = ac + bci + adi + bd i^2 \\ & = (ac - bd) + (bc + ad)i.\end{split}\]</div> <p>This explains the definition of <code class="docutils literal notranslate"><span class="pre">Mul</span></code> below.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Zero</span><span class="w"> </span><span class="n">GaussInt</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">⟨⟨</span><span class="mi">0</span><span class="o">,</span><span class="w"> </span><span class="mi">0</span><span class="o">⟩⟩</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span> <span class="o">:</span> <span class="n">Zero</span> <span class="n">GaussInt</span> <span class="o">:=</span> <span class="o">⟨⟨</span><span class="mi">0</span><span class="o">,</span> <span class="mi">0</span><span class="o">⟩⟩</span> <span class="kd">instance</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">One</span><span class="w"> </span><span class="n">GaussInt</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">⟨⟨</span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="mi">0</span><span class="o">⟩⟩</span> <span class="kd">instance</span> <span class="o">:</span> <span class="n">One</span> <span class="n">GaussInt</span> <span class="o">:=</span> <span class="o">⟨⟨</span><span class="mi">1</span><span class="o">,</span> <span class="mi">0</span><span class="o">⟩⟩</span> <span class="kd">instance</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Add</span><span class="w"> </span><span class="n">GaussInt</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">⟨</span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="o">⟨</span><span class="n">x.re</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y.re</span><span class="o">,</span><span class="w"> </span><span class="n">x.im</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y.im</span><span class="o">⟩⟩</span> <span class="kd">instance</span> <span class="o">:</span> <span class="n">Add</span> <span class="n">GaussInt</span> <span class="o">:=</span> <span class="o">⟨</span><span class="k">fun</span> <span class="n">x</span> <span class="n">y</span> <span class="bp">↦</span> <span class="o">⟨</span><span class="n">x.re</span> <span class="bp">+</span> <span class="n">y.re</span><span class="o">,</span> <span class="n">x.im</span> <span class="bp">+</span> <span class="n">y.im</span><span class="o">⟩⟩</span> <span class="kd">instance</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Neg</span><span class="w"> </span><span class="n">GaussInt</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">⟨</span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="o">⟨</span><span class="bp">-</span><span class="n">x.re</span><span class="o">,</span><span class="w"> </span><span class="bp">-</span><span class="n">x.im</span><span class="o">⟩⟩</span> <span class="kd">instance</span> <span class="o">:</span> <span class="n">Neg</span> <span class="n">GaussInt</span> <span class="o">:=</span> <span class="o">⟨</span><span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="o">⟨</span><span class="bp">-</span><span class="n">x.re</span><span class="o">,</span> <span class="bp">-</span><span class="n">x.im</span><span class="o">⟩⟩</span> <span class="kd">instance</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Mul</span><span class="w"> </span><span class="n">GaussInt</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">⟨</span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="o">⟨</span><span class="n">x.re</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y.re</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">x.im</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y.im</span><span class="o">,</span><span class="w"> </span><span class="n">x.re</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y.im</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">x.im</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y.re</span><span class="o">⟩⟩</span> <span class="kd">instance</span> <span class="o">:</span> <span class="n">Mul</span> <span class="n">GaussInt</span> <span class="o">:=</span> <span class="o">⟨</span><span class="k">fun</span> <span class="n">x</span> <span class="n">y</span> <span class="bp">↦</span> <span class="o">⟨</span><span class="n">x.re</span> <span class="bp">*</span> <span class="n">y.re</span> <span class="bp">-</span> <span class="n">x.im</span> <span class="bp">*</span> <span class="n">y.im</span><span class="o">,</span> <span class="n">x.re</span> <span class="bp">*</span> <span class="n">y.im</span> <span class="bp">+</span> <span class="n">x.im</span> <span class="bp">*</span> <span class="n">y.re</span><span class="o">⟩⟩</span> </pre></div> </div> <p>As noted in <a class="reference internal" href="#section-structures"><span class="std std-numref">Section 6.1</span></a>, it is a good idea to put all the definitions
-
@@ -1075,64 +1071,64 @@ files associated with this chapter, these definitions are made in the<code class="docutils literal notranslate"><span class="pre">GaussInt.zero</span></code> and the like and assigning the notation to those. It is often useful to have an explicit name for the definitions, for example, to use with <code class="docutils literal notranslate"><span class="pre">simp</span></code> and <code class="docutils literal notranslate"><span class="pre">rewrite</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">zero_def</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="mi">0</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">⟨</span><span class="mi">0</span><span class="o">,</span><span class="w"> </span><span class="mi">0</span><span class="o">⟩</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">zero_def</span> <span class="o">:</span> <span class="o">(</span><span class="mi">0</span> <span class="o">:</span> <span class="n">GaussInt</span><span class="o">)</span> <span class="bp">=</span> <span class="o">⟨</span><span class="mi">0</span><span class="o">,</span> <span class="mi">0</span><span class="o">⟩</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">one_def</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="mi">1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">⟨</span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="mi">0</span><span class="o">⟩</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">theorem</span> <span class="n">one_def</span> <span class="o">:</span> <span class="o">(</span><span class="mi">1</span> <span class="o">:</span> <span class="n">GaussInt</span><span class="o">)</span> <span class="bp">=</span> <span class="o">⟨</span><span class="mi">1</span><span class="o">,</span> <span class="mi">0</span><span class="o">⟩</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">add_def</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">⟨</span><span class="n">x.re</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y.re</span><span class="o">,</span><span class="w"> </span><span class="n">x.im</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y.im</span><span class="o">⟩</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">theorem</span> <span class="n">add_def</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">GaussInt</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">y</span> <span class="bp">=</span> <span class="o">⟨</span><span class="n">x.re</span> <span class="bp">+</span> <span class="n">y.re</span><span class="o">,</span> <span class="n">x.im</span> <span class="bp">+</span> <span class="n">y.im</span><span class="o">⟩</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">neg_def</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">-</span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">⟨</span><span class="bp">-</span><span class="n">x.re</span><span class="o">,</span><span class="w"> </span><span class="bp">-</span><span class="n">x.im</span><span class="o">⟩</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">theorem</span> <span class="n">neg_def</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">GaussInt</span><span class="o">)</span> <span class="o">:</span> <span class="bp">-</span><span class="n">x</span> <span class="bp">=</span> <span class="o">⟨</span><span class="bp">-</span><span class="n">x.re</span><span class="o">,</span> <span class="bp">-</span><span class="n">x.im</span><span class="o">⟩</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">mul_def</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">⟨</span><span class="n">x.re</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y.re</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">x.im</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y.im</span><span class="o">,</span><span class="w"> </span><span class="n">x.re</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y.im</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">x.im</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y.re</span><span class="o">⟩</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">theorem</span> <span class="n">mul_def</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">GaussInt</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">*</span> <span class="n">y</span> <span class="bp">=</span> <span class="o">⟨</span><span class="n">x.re</span> <span class="bp">*</span> <span class="n">y.re</span> <span class="bp">-</span> <span class="n">x.im</span> <span class="bp">*</span> <span class="n">y.im</span><span class="o">,</span> <span class="n">x.re</span> <span class="bp">*</span> <span class="n">y.im</span> <span class="bp">+</span> <span class="n">x.im</span> <span class="bp">*</span> <span class="n">y.re</span><span class="o">⟩</span> <span class="o">:=</span> <span class="n">rfl</span> </pre></div> </div> <p>It is also useful to name the rules that compute the real and imaginary parts, and to declare them to the simplifier.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">@[</span><span class="n">simp</span><span class="kd">]</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">zero_re</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="mi">0</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="o">)</span><span class="bp">.</span><span class="n">re</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">@[simp]</span> <span class="kd">theorem</span> <span class="n">zero_re</span> <span class="o">:</span> <span class="o">(</span><span class="mi">0</span> <span class="o">:</span> <span class="n">GaussInt</span><span class="o">)</span><span class="bp">.</span><span class="n">re</span> <span class="bp">=</span> <span class="mi">0</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="kd">@[</span><span class="n">simp</span><span class="kd">]</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">zero_im</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="mi">0</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="o">)</span><span class="bp">.</span><span class="n">im</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">@[simp]</span> <span class="kd">theorem</span> <span class="n">zero_im</span> <span class="o">:</span> <span class="o">(</span><span class="mi">0</span> <span class="o">:</span> <span class="n">GaussInt</span><span class="o">)</span><span class="bp">.</span><span class="n">im</span> <span class="bp">=</span> <span class="mi">0</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="kd">@[</span><span class="n">simp</span><span class="kd">]</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">one_re</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="mi">1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="o">)</span><span class="bp">.</span><span class="n">re</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">@[simp]</span> <span class="kd">theorem</span> <span class="n">one_re</span> <span class="o">:</span> <span class="o">(</span><span class="mi">1</span> <span class="o">:</span> <span class="n">GaussInt</span><span class="o">)</span><span class="bp">.</span><span class="n">re</span> <span class="bp">=</span> <span class="mi">1</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="kd">@[</span><span class="n">simp</span><span class="kd">]</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">one_im</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="mi">1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="o">)</span><span class="bp">.</span><span class="n">im</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">@[simp]</span> <span class="kd">theorem</span> <span class="n">one_im</span> <span class="o">:</span> <span class="o">(</span><span class="mi">1</span> <span class="o">:</span> <span class="n">GaussInt</span><span class="o">)</span><span class="bp">.</span><span class="n">im</span> <span class="bp">=</span> <span class="mi">0</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="kd">@[</span><span class="n">simp</span><span class="kd">]</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">add_re</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="bp">.</span><span class="n">re</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x.re</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y.re</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">@[simp]</span> <span class="kd">theorem</span> <span class="n">add_re</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">GaussInt</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">x</span> <span class="bp">+</span> <span class="n">y</span><span class="o">)</span><span class="bp">.</span><span class="n">re</span> <span class="bp">=</span> <span class="n">x.re</span> <span class="bp">+</span> <span class="n">y.re</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="kd">@[</span><span class="n">simp</span><span class="kd">]</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">add_im</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="bp">.</span><span class="n">im</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x.im</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y.im</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">@[simp]</span> <span class="kd">theorem</span> <span class="n">add_im</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">GaussInt</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">x</span> <span class="bp">+</span> <span class="n">y</span><span class="o">)</span><span class="bp">.</span><span class="n">im</span> <span class="bp">=</span> <span class="n">x.im</span> <span class="bp">+</span> <span class="n">y.im</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="kd">@[</span><span class="n">simp</span><span class="kd">]</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">neg_re</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="bp">-</span><span class="n">x</span><span class="o">)</span><span class="bp">.</span><span class="n">re</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">-</span><span class="n">x.re</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">@[simp]</span> <span class="kd">theorem</span> <span class="n">neg_re</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">GaussInt</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="bp">-</span><span class="n">x</span><span class="o">)</span><span class="bp">.</span><span class="n">re</span> <span class="bp">=</span> <span class="bp">-</span><span class="n">x.re</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="kd">@[</span><span class="n">simp</span><span class="kd">]</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">neg_im</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="bp">-</span><span class="n">x</span><span class="o">)</span><span class="bp">.</span><span class="n">im</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">-</span><span class="n">x.im</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">@[simp]</span> <span class="kd">theorem</span> <span class="n">neg_im</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">GaussInt</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="bp">-</span><span class="n">x</span><span class="o">)</span><span class="bp">.</span><span class="n">im</span> <span class="bp">=</span> <span class="bp">-</span><span class="n">x.im</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="kd">@[</span><span class="n">simp</span><span class="kd">]</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">mul_re</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="bp">.</span><span class="n">re</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x.re</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y.re</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">x.im</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y.im</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">@[simp]</span> <span class="kd">theorem</span> <span class="n">mul_re</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">GaussInt</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">x</span> <span class="bp">*</span> <span class="n">y</span><span class="o">)</span><span class="bp">.</span><span class="n">re</span> <span class="bp">=</span> <span class="n">x.re</span> <span class="bp">*</span> <span class="n">y.re</span> <span class="bp">-</span> <span class="n">x.im</span> <span class="bp">*</span> <span class="n">y.im</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="kd">@[</span><span class="n">simp</span><span class="kd">]</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">mul_im</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="bp">.</span><span class="n">im</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x.re</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y.im</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">x.im</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y.re</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">@[simp]</span> <span class="kd">theorem</span> <span class="n">mul_im</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">GaussInt</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">x</span> <span class="bp">*</span> <span class="n">y</span><span class="o">)</span><span class="bp">.</span><span class="n">im</span> <span class="bp">=</span> <span class="n">x.re</span> <span class="bp">*</span> <span class="n">y.im</span> <span class="bp">+</span> <span class="n">x.im</span> <span class="bp">*</span> <span class="n">y.re</span> <span class="o">:=</span> <span class="n">rfl</span> </pre></div> </div> <p>It is now surprisingly easy to show that the Gaussian integers are an instance
-
@@ -1156,63 +1152,63 @@ to reduce the identities to their real and imaginary components,simplifying, and, if necessary, carrying out the relevant ring calculation in the integers. Note that we could easily avoid repeating all this code, but this is not the topic of the current discussion.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span><span class="w"> </span><span class="n">instCommRing</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">CommRing</span><span class="w"> </span><span class="n">GaussInt</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">zero</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="mi">0</span> <span class="w"> </span><span class="n">one</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="mi">1</span> <span class="w"> </span><span class="n">add</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">(</span><span class="bp">·</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="bp">·</span><span class="o">)</span> <span class="w"> </span><span class="n">neg</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="bp">-</span><span class="n">x</span> <span class="w"> </span><span class="n">mul</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">(</span><span class="bp">·</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="bp">·</span><span class="o">)</span> <span class="w"> </span><span class="n">nsmul</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">nsmulRec</span> <span class="w"> </span><span class="n">zsmul</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">zsmulRec</span> <span class="w"> </span><span class="n">add_assoc</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intros</span> <span class="w"> </span><span class="n">ext</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">ring</span> <span class="w"> </span><span class="n">zero_add</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span> <span class="w"> </span><span class="n">ext</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">simp</span> <span class="w"> </span><span class="n">add_zero</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span> <span class="w"> </span><span class="n">ext</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">simp</span> <span class="w"> </span><span class="n">neg_add_cancel</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span> <span class="w"> </span><span class="n">ext</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">simp</span> <span class="w"> </span><span class="n">add_comm</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intros</span> <span class="w"> </span><span class="n">ext</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">ring</span> <span class="w"> </span><span class="n">mul_assoc</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intros</span> <span class="w"> </span><span class="n">ext</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">ring</span> <span class="w"> </span><span class="n">one_mul</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span> <span class="w"> </span><span class="n">ext</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">simp</span> <span class="w"> </span><span class="n">mul_one</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span> <span class="w"> </span><span class="n">ext</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">simp</span> <span class="w"> </span><span class="n">left_distrib</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intros</span> <span class="w"> </span><span class="n">ext</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">ring</span> <span class="w"> </span><span class="n">right_distrib</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intros</span> <span class="w"> </span><span class="n">ext</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">ring</span> <span class="w"> </span><span class="n">mul_comm</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intros</span> <span class="w"> </span><span class="n">ext</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">ring</span> <span class="w"> </span><span class="n">zero_mul</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intros</span> <span class="w"> </span><span class="n">ext</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">simp</span> <span class="w"> </span><span class="n">mul_zero</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intros</span> <span class="w"> </span><span class="n">ext</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">simp</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span> <span class="n">instCommRing</span> <span class="o">:</span> <span class="n">CommRing</span> <span class="n">GaussInt</span> <span class="n">where</span> <span class="n">zero</span> <span class="o">:=</span> <span class="mi">0</span> <span class="n">one</span> <span class="o">:=</span> <span class="mi">1</span> <span class="n">add</span> <span class="o">:=</span> <span class="o">(</span><span class="bp">·</span> <span class="bp">+</span> <span class="bp">·</span><span class="o">)</span> <span class="n">neg</span> <span class="n">x</span> <span class="o">:=</span> <span class="bp">-</span><span class="n">x</span> <span class="n">mul</span> <span class="o">:=</span> <span class="o">(</span><span class="bp">·</span> <span class="bp">*</span> <span class="bp">·</span><span class="o">)</span> <span class="n">nsmul</span> <span class="o">:=</span> <span class="n">nsmulRec</span> <span class="n">zsmul</span> <span class="o">:=</span> <span class="n">zsmulRec</span> <span class="n">add_assoc</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intros</span> <span class="n">ext</span> <span class="bp"><;></span> <span class="n">simp</span> <span class="bp"><;></span> <span class="n">ring</span> <span class="n">zero_add</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">ext</span> <span class="bp"><;></span> <span class="n">simp</span> <span class="n">add_zero</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">ext</span> <span class="bp"><;></span> <span class="n">simp</span> <span class="n">neg_add_cancel</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">ext</span> <span class="bp"><;></span> <span class="n">simp</span> <span class="n">add_comm</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intros</span> <span class="n">ext</span> <span class="bp"><;></span> <span class="n">simp</span> <span class="bp"><;></span> <span class="n">ring</span> <span class="n">mul_assoc</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intros</span> <span class="n">ext</span> <span class="bp"><;></span> <span class="n">simp</span> <span class="bp"><;></span> <span class="n">ring</span> <span class="n">one_mul</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">ext</span> <span class="bp"><;></span> <span class="n">simp</span> <span class="n">mul_one</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">ext</span> <span class="bp"><;></span> <span class="n">simp</span> <span class="n">left_distrib</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intros</span> <span class="n">ext</span> <span class="bp"><;></span> <span class="n">simp</span> <span class="bp"><;></span> <span class="n">ring</span> <span class="n">right_distrib</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intros</span> <span class="n">ext</span> <span class="bp"><;></span> <span class="n">simp</span> <span class="bp"><;></span> <span class="n">ring</span> <span class="n">mul_comm</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intros</span> <span class="n">ext</span> <span class="bp"><;></span> <span class="n">simp</span> <span class="bp"><;></span> <span class="n">ring</span> <span class="n">zero_mul</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intros</span> <span class="n">ext</span> <span class="bp"><;></span> <span class="n">simp</span> <span class="n">mul_zero</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intros</span> <span class="n">ext</span> <span class="bp"><;></span> <span class="n">simp</span> </pre></div> </div> <p>Lean’s library defines the class of <em>nontrivial</em> types to be types with at least two distinct elements. In the context of a ring, this is equivalent to saying that the zero is not equal to the one. Since some common theorems depend on that fact, we may as well establish it now.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nontrivial</span><span class="w"> </span><span class="n">GaussInt</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="mi">0</span><span class="o">,</span><span class="w"> </span><span class="mi">1</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">Ne</span><span class="o">,</span><span class="w"> </span><span class="n">GaussInt.ext_iff</span><span class="o">]</span> <span class="w"> </span><span class="n">simp</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span> <span class="o">:</span> <span class="n">Nontrivial</span> <span class="n">GaussInt</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">use</span> <span class="mi">0</span><span class="o">,</span> <span class="mi">1</span> <span class="n">rw</span> <span class="o">[</span><span class="n">Ne</span><span class="o">,</span> <span class="n">GaussInt.ext_iff</span><span class="o">]</span> <span class="n">simp</span> </pre></div> </div> <p>We will now show that the Gaussian integers have an important additional
-
@@ -1230,14 +1226,14 @@ In that case, we can take <span class="math notranslate nohighlight">\(q\)</spanresult of integer division of <span class="math notranslate nohighlight">\(a\)</span> by <span class="math notranslate nohighlight">\(b\)</span> and <span class="math notranslate nohighlight">\(r\)</span> to be the remainder. These functions are defined in Lean so that the satisfy the following:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℤ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">%</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Eq.symm</span><span class="w"> </span><span class="o">(</span><span class="n">Int.ediv_add_emod</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">ℤ</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">=</span> <span class="n">b</span> <span class="bp">*</span> <span class="o">(</span><span class="n">a</span> <span class="bp">/</span> <span class="n">b</span><span class="o">)</span> <span class="bp">+</span> <span class="n">a</span> <span class="bp">%</span> <span class="n">b</span> <span class="o">:=</span> <span class="n">Eq.symm</span> <span class="o">(</span><span class="n">Int.ediv_add_emod</span> <span class="n">a</span> <span class="n">b</span><span class="o">)</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℤ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">%</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Int.emod_nonneg</span><span class="w"> </span><span class="n">a</span> <span class="kd">example</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">ℤ</span><span class="o">)</span> <span class="o">:</span> <span class="n">b</span> <span class="bp">≠</span> <span class="mi">0</span> <span class="bp">→</span> <span class="mi">0</span> <span class="bp">≤</span> <span class="n">a</span> <span class="bp">%</span> <span class="n">b</span> <span class="o">:=</span> <span class="n">Int.emod_nonneg</span> <span class="n">a</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℤ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">%</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="bp">|</span><span class="n">b</span><span class="bp">|</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Int.emod_lt</span><span class="w"> </span><span class="n">a</span> <span class="kd">example</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">ℤ</span><span class="o">)</span> <span class="o">:</span> <span class="n">b</span> <span class="bp">≠</span> <span class="mi">0</span> <span class="bp">→</span> <span class="n">a</span> <span class="bp">%</span> <span class="n">b</span> <span class="bp"><</span> <span class="bp">|</span><span class="n">b</span><span class="bp">|</span> <span class="o">:=</span> <span class="n">Int.emod_lt</span> <span class="n">a</span> </pre></div> </div> <p>In an arbitrary ring, an element <span class="math notranslate nohighlight">\(a\)</span> is said to be a <em>unit</em> if it divides
-
@@ -1272,7 +1268,7 @@ we have <span class="math notranslate nohighlight">\(N(xy) = N(x)N(y)\)</span>.<<p>To see that this definition of the norm makes the Gaussian integers a Euclidean domain, only the first property is challenging. Suppose we want to write <span class="math notranslate nohighlight">\(a + bi = (c + di) q + r\)</span> for suitable <span class="math notranslate nohighlight">\(q\)</span> and <span class="math notranslate nohighlight">\(r\)</span>. Treating <span class="math notranslate nohighlight">\(a + bi\)</span> and <span class="math notranslate nohighlight">\(c + di\)</span> are complex and <span class="math notranslate nohighlight">\(r\)</span>. Treating <span class="math notranslate nohighlight">\(a + bi\)</span> and <span class="math notranslate nohighlight">\(c + di\)</span> as complex numbers, carry out the division</p> <div class="math notranslate nohighlight"> \[\frac{a + bi}{c + di} = \frac{(a + bi)(c - di)}{(c + di)(c-di)} =
-
@@ -1303,9 +1299,9 @@ where the Gaussian integers themselves are constructed as a special caseof a ring of <em>quadratic integers</em>. See the file <a class="reference external" href="https://github.com/leanprover-community/mathlib4/blob/master/Mathlib/NumberTheory/Zsqrtd/GaussianInt.lean">GaussianInt.lean</a>.</p> <p>Here we will instead carry out an argument that stays in the integers. This illustrates an choice one commonly faces when formalizing mathematics. This illustrates a choice one commonly faces when formalizing mathematics. Given an argument that requires concepts or machinery that is not already in the library, one has two choices: either formalizes the concepts or machinery in the library, one has two choices: either formalize the concepts or machinery needed, or adapt the argument to make use of concepts and machinery you already have. The first choice is generally a good investment of time when the results
-
@@ -1325,38 +1321,37 @@ We are grateful to Heather Macbeth for suggesting the following moreelegant approach, which avoids definition by cases. We simply add <code class="docutils literal notranslate"><span class="pre">b</span> <span class="pre">/</span> <span class="pre">2</span></code> to <code class="docutils literal notranslate"><span class="pre">a</span></code> before dividing and then subtract it from the remainder.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">div'</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℤ</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="n">b</span> <span class="kd">def</span><span class="w"> </span><span class="n">mod'</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℤ</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="bp">%</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">div'_add_mod'</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℤ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">div'</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">mod'</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">div'</span><span class="o">,</span><span class="w"> </span><span class="n">mod'</span><span class="o">]</span> <span class="w"> </span><span class="n">linarith</span><span class="w"> </span><span class="o">[</span><span class="n">Int.ediv_add_emod</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="n">b</span><span class="o">]</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">abs_mod'_le</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℤ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">|</span><span class="n">mod'</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="bp">|</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">mod'</span><span class="o">,</span><span class="w"> </span><span class="n">abs_le</span><span class="o">]</span> <span class="w"> </span><span class="n">constructor</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">linarith</span><span class="w"> </span><span class="o">[</span><span class="n">Int.emod_nonneg</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="n">h.ne'</span><span class="o">]</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Int.emod_lt_of_pos</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Int.ediv_add_emod</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="mi">2</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Int.emod_lt_of_pos</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">zero_lt_two</span> <span class="w"> </span><span class="n">revert</span><span class="w"> </span><span class="n">this</span><span class="bp">;</span><span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">this</span><span class="w"> </span><span class="c1">-- FIXME, this should not be needed</span> <span class="w"> </span><span class="n">linarith</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">div'</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">ℤ</span><span class="o">)</span> <span class="o">:=</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">/</span> <span class="mi">2</span><span class="o">)</span> <span class="bp">/</span> <span class="n">b</span> <span class="kd">def</span> <span class="n">mod'</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">ℤ</span><span class="o">)</span> <span class="o">:=</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">/</span> <span class="mi">2</span><span class="o">)</span> <span class="bp">%</span> <span class="n">b</span> <span class="bp">-</span> <span class="n">b</span> <span class="bp">/</span> <span class="mi">2</span> <span class="kd">theorem</span> <span class="n">div'_add_mod'</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">ℤ</span><span class="o">)</span> <span class="o">:</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">div'</span> <span class="n">a</span> <span class="n">b</span> <span class="bp">+</span> <span class="n">mod'</span> <span class="n">a</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">a</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">div'</span><span class="o">,</span> <span class="n">mod'</span><span class="o">]</span> <span class="n">linarith</span> <span class="o">[</span><span class="n">Int.ediv_add_emod</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">/</span> <span class="mi">2</span><span class="o">)</span> <span class="n">b</span><span class="o">]</span> <span class="kd">theorem</span> <span class="n">abs_mod'_le</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">ℤ</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp"><</span> <span class="n">b</span><span class="o">)</span> <span class="o">:</span> <span class="bp">|</span><span class="n">mod'</span> <span class="n">a</span> <span class="n">b</span><span class="bp">|</span> <span class="bp">≤</span> <span class="n">b</span> <span class="bp">/</span> <span class="mi">2</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">mod'</span><span class="o">,</span> <span class="n">abs_le</span><span class="o">]</span> <span class="n">constructor</span> <span class="bp">·</span> <span class="n">linarith</span> <span class="o">[</span><span class="n">Int.emod_nonneg</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">/</span> <span class="mi">2</span><span class="o">)</span> <span class="n">h.ne'</span><span class="o">]</span> <span class="k">have</span> <span class="o">:=</span> <span class="n">Int.emod_lt_of_pos</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">/</span> <span class="mi">2</span><span class="o">)</span> <span class="n">h</span> <span class="k">have</span> <span class="o">:=</span> <span class="n">Int.ediv_add_emod</span> <span class="n">b</span> <span class="mi">2</span> <span class="k">have</span> <span class="o">:=</span> <span class="n">Int.emod_lt_of_pos</span> <span class="n">b</span> <span class="n">zero_lt_two</span> <span class="n">linarith</span> </pre></div> </div> <p>Note the use of our old friend, <code class="docutils literal notranslate"><span class="pre">linarith</span></code>. We will also need to express <code class="docutils literal notranslate"><span class="pre">mod'</span></code> in terms of <code class="docutils literal notranslate"><span class="pre">div'</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">mod'_eq</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℤ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">mod'</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">div'</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">linarith</span><span class="w"> </span><span class="o">[</span><span class="n">div'_add_mod'</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">mod'_eq</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">ℤ</span><span class="o">)</span> <span class="o">:</span> <span class="n">mod'</span> <span class="n">a</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">-</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">div'</span> <span class="n">a</span> <span class="n">b</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">linarith</span> <span class="o">[</span><span class="n">div'_add_mod'</span> <span class="n">a</span> <span class="n">b</span><span class="o">]</span> </pre></div> </div> <p>We will use the fact that <span class="math notranslate nohighlight">\(x^2 + y^2\)</span> is equal to zero if and only if <span class="math notranslate nohighlight">\(x\)</span> and <span class="math notranslate nohighlight">\(y\)</span> are both zero. As an exercise, we ask you to prove that this holds in any ordered ring.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">sq_add_sq_eq_zero</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">LinearOrderedRing</span><span class="w"> </span><span class="n">α</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">sq_add_sq_eq_zero</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">LinearOrderedRing</span> <span class="n">α</span><span class="o">]</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">α</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">+</span> <span class="n">y</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">=</span> <span class="mi">0</span> <span class="bp">↔</span> <span class="n">x</span> <span class="bp">=</span> <span class="mi">0</span> <span class="bp">∧</span> <span class="n">y</span> <span class="bp">=</span> <span class="mi">0</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>We will put all the remaining definitions and theorems in this section
-
@@ -1364,33 +1359,33 @@ in the <code class="docutils literal notranslate"><span class="pre">GaussInt</spFirst, we define the <code class="docutils literal notranslate"><span class="pre">norm</span></code> function and ask you to establish some of its properties. The proofs are all short.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">norm</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">x.re</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">x.im</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span> <span class="kd">@[</span><span class="n">simp</span><span class="kd">]</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">norm_nonneg</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">norm</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">norm_eq_zero</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">norm</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">norm_pos</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">norm</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">norm_mul</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">norm</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">norm</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">norm</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">norm</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">GaussInt</span><span class="o">)</span> <span class="o">:=</span> <span class="n">x.re</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">+</span> <span class="n">x.im</span> <span class="bp">^</span> <span class="mi">2</span> <span class="kd">@[simp]</span> <span class="kd">theorem</span> <span class="n">norm_nonneg</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">GaussInt</span><span class="o">)</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp">≤</span> <span class="n">norm</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">theorem</span> <span class="n">norm_eq_zero</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">GaussInt</span><span class="o">)</span> <span class="o">:</span> <span class="n">norm</span> <span class="n">x</span> <span class="bp">=</span> <span class="mi">0</span> <span class="bp">↔</span> <span class="n">x</span> <span class="bp">=</span> <span class="mi">0</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">theorem</span> <span class="n">norm_pos</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">GaussInt</span><span class="o">)</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp"><</span> <span class="n">norm</span> <span class="n">x</span> <span class="bp">↔</span> <span class="n">x</span> <span class="bp">≠</span> <span class="mi">0</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">theorem</span> <span class="n">norm_mul</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">GaussInt</span><span class="o">)</span> <span class="o">:</span> <span class="n">norm</span> <span class="o">(</span><span class="n">x</span> <span class="bp">*</span> <span class="n">y</span><span class="o">)</span> <span class="bp">=</span> <span class="n">norm</span> <span class="n">x</span> <span class="bp">*</span> <span class="n">norm</span> <span class="n">y</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>Next we define the conjugate function:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">conj</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">⟨</span><span class="n">x.re</span><span class="o">,</span><span class="w"> </span><span class="bp">-</span><span class="n">x.im</span><span class="o">⟩</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">conj</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">GaussInt</span><span class="o">)</span> <span class="o">:</span> <span class="n">GaussInt</span> <span class="o">:=</span> <span class="o">⟨</span><span class="n">x.re</span><span class="o">,</span> <span class="bp">-</span><span class="n">x.im</span><span class="o">⟩</span> <span class="kd">@[</span><span class="n">simp</span><span class="kd">]</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">conj_re</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">conj</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="bp">.</span><span class="n">re</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x.re</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">@[simp]</span> <span class="kd">theorem</span> <span class="n">conj_re</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">GaussInt</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">conj</span> <span class="n">x</span><span class="o">)</span><span class="bp">.</span><span class="n">re</span> <span class="bp">=</span> <span class="n">x.re</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="kd">@[</span><span class="n">simp</span><span class="kd">]</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">conj_im</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">conj</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="bp">.</span><span class="n">im</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">-</span><span class="n">x.im</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">@[simp]</span> <span class="kd">theorem</span> <span class="n">conj_im</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">GaussInt</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">conj</span> <span class="n">x</span><span class="o">)</span><span class="bp">.</span><span class="n">im</span> <span class="bp">=</span> <span class="bp">-</span><span class="n">x.im</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">norm_conj</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">norm</span><span class="w"> </span><span class="o">(</span><span class="n">conj</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">norm</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="o">[</span><span class="n">norm</span><span class="o">]</span> <span class="kd">theorem</span> <span class="n">norm_conj</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">GaussInt</span><span class="o">)</span> <span class="o">:</span> <span class="n">norm</span> <span class="o">(</span><span class="n">conj</span> <span class="n">x</span><span class="o">)</span> <span class="bp">=</span> <span class="n">norm</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> <span class="o">[</span><span class="n">norm</span><span class="o">]</span> </pre></div> </div> <p>Finally, we define division for the Gaussian integers
-
@@ -1403,23 +1398,23 @@ then the real and imaginary parts of <code class="docutils literal notranslate"><p>respectively. Here the numerators are the real and imaginary parts of <span class="math notranslate nohighlight">\((a + bi) (c - di)\)</span>, and the denominators are both equal to the norm of <span class="math notranslate nohighlight">\(c + di\)</span>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Div</span><span class="w"> </span><span class="n">GaussInt</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">⟨</span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="o">⟨</span><span class="n">Int.div'</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">conj</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="bp">.</span><span class="n">re</span><span class="w"> </span><span class="o">(</span><span class="n">norm</span><span class="w"> </span><span class="n">y</span><span class="o">),</span><span class="w"> </span><span class="n">Int.div'</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">conj</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="bp">.</span><span class="n">im</span><span class="w"> </span><span class="o">(</span><span class="n">norm</span><span class="w"> </span><span class="n">y</span><span class="o">)⟩⟩</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span> <span class="o">:</span> <span class="n">Div</span> <span class="n">GaussInt</span> <span class="o">:=</span> <span class="o">⟨</span><span class="k">fun</span> <span class="n">x</span> <span class="n">y</span> <span class="bp">↦</span> <span class="o">⟨</span><span class="n">Int.div'</span> <span class="o">(</span><span class="n">x</span> <span class="bp">*</span> <span class="n">conj</span> <span class="n">y</span><span class="o">)</span><span class="bp">.</span><span class="n">re</span> <span class="o">(</span><span class="n">norm</span> <span class="n">y</span><span class="o">),</span> <span class="n">Int.div'</span> <span class="o">(</span><span class="n">x</span> <span class="bp">*</span> <span class="n">conj</span> <span class="n">y</span><span class="o">)</span><span class="bp">.</span><span class="n">im</span> <span class="o">(</span><span class="n">norm</span> <span class="n">y</span><span class="o">)⟩⟩</span> </pre></div> </div> <p>Having defined <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">/</span> <span class="pre">y</span></code>, We define <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">%</span> <span class="pre">y</span></code> to be the remainder, <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">-</span> <span class="pre">(x</span> <span class="pre">/</span> <span class="pre">y)</span> <span class="pre">*</span> <span class="pre">y</span></code>. As above, we record the definitions in the theorems <code class="docutils literal notranslate"><span class="pre">div_def</span></code> and <code class="docutils literal notranslate"><span class="pre">mod_def</span></code> so that we can use them with <code class="docutils literal notranslate"><span class="pre">simp</span></code> and <code class="docutils literal notranslate"><span class="pre">rewrite</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Mod</span><span class="w"> </span><span class="n">GaussInt</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">⟨</span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="n">y</span><span class="o">)⟩</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span> <span class="o">:</span> <span class="n">Mod</span> <span class="n">GaussInt</span> <span class="o">:=</span> <span class="o">⟨</span><span class="k">fun</span> <span class="n">x</span> <span class="n">y</span> <span class="bp">↦</span> <span class="n">x</span> <span class="bp">-</span> <span class="n">y</span> <span class="bp">*</span> <span class="o">(</span><span class="n">x</span> <span class="bp">/</span> <span class="n">y</span><span class="o">)⟩</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">div_def</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">⟨</span><span class="n">Int.div'</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">conj</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="bp">.</span><span class="n">re</span><span class="w"> </span><span class="o">(</span><span class="n">norm</span><span class="w"> </span><span class="n">y</span><span class="o">),</span><span class="w"> </span><span class="n">Int.div'</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">conj</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="bp">.</span><span class="n">im</span><span class="w"> </span><span class="o">(</span><span class="n">norm</span><span class="w"> </span><span class="n">y</span><span class="o">)⟩</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">theorem</span> <span class="n">div_def</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">GaussInt</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">/</span> <span class="n">y</span> <span class="bp">=</span> <span class="o">⟨</span><span class="n">Int.div'</span> <span class="o">(</span><span class="n">x</span> <span class="bp">*</span> <span class="n">conj</span> <span class="n">y</span><span class="o">)</span><span class="bp">.</span><span class="n">re</span> <span class="o">(</span><span class="n">norm</span> <span class="n">y</span><span class="o">),</span> <span class="n">Int.div'</span> <span class="o">(</span><span class="n">x</span> <span class="bp">*</span> <span class="n">conj</span> <span class="n">y</span><span class="o">)</span><span class="bp">.</span><span class="n">im</span> <span class="o">(</span><span class="n">norm</span> <span class="n">y</span><span class="o">)⟩</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">mod_def</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">%</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">theorem</span> <span class="n">mod_def</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">GaussInt</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">%</span> <span class="n">y</span> <span class="bp">=</span> <span class="n">x</span> <span class="bp">-</span> <span class="n">y</span> <span class="bp">*</span> <span class="o">(</span><span class="n">x</span> <span class="bp">/</span> <span class="n">y</span><span class="o">)</span> <span class="o">:=</span> <span class="n">rfl</span> </pre></div> </div> <p>These definitions immediately yield <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">=</span> <span class="pre">y</span> <span class="pre">*</span> <span class="pre">(x</span> <span class="pre">/</span> <span class="pre">y)</span> <span class="pre">+</span> <span class="pre">x</span> <span class="pre">%</span> <span class="pre">y</span></code> for every
-
@@ -1447,24 +1442,24 @@ So we have</p>as required.</p> <p>This messy calculation is carried out in the next proof. We encourage you to step through the details and see if you can find a nicer argument.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">norm_mod_lt</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="o">)</span><span class="w"> </span><span class="o">{</span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hy</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">%</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="bp">.</span><span class="n">norm</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">y.norm</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">norm_y_pos</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">norm</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">rwa</span><span class="w"> </span><span class="o">[</span><span class="n">norm_pos</span><span class="o">]</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">H1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">%</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">conj</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">⟨</span><span class="n">Int.mod'</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">conj</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="bp">.</span><span class="n">re</span><span class="w"> </span><span class="o">(</span><span class="n">norm</span><span class="w"> </span><span class="n">y</span><span class="o">),</span><span class="w"> </span><span class="n">Int.mod'</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">conj</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="bp">.</span><span class="n">im</span><span class="w"> </span><span class="o">(</span><span class="n">norm</span><span class="w"> </span><span class="n">y</span><span class="o">)⟩</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">ext</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="o">[</span><span class="n">Int.mod'_eq</span><span class="o">,</span><span class="w"> </span><span class="n">mod_def</span><span class="o">,</span><span class="w"> </span><span class="n">div_def</span><span class="o">,</span><span class="w"> </span><span class="n">norm</span><span class="o">]</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">ring</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">H2</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">norm</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">%</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">norm</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">norm</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">norm</span><span class="w"> </span><span class="n">y</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="k">calc</span> <span class="w"> </span><span class="n">norm</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">%</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">norm</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">norm</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">%</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">conj</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="n">only</span><span class="w"> </span><span class="o">[</span><span class="n">norm_mul</span><span class="o">,</span><span class="w"> </span><span class="n">norm_conj</span><span class="o">]</span> <span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">|</span><span class="n">Int.mod'</span><span class="w"> </span><span class="o">(</span><span class="n">x.re</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y.re</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">x.im</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y.im</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">norm</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="bp">|</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span> <span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="bp">|</span><span class="n">Int.mod'</span><span class="w"> </span><span class="o">(</span><span class="bp">-</span><span class="o">(</span><span class="n">x.re</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y.im</span><span class="o">)</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">x.im</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y.re</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">norm</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="bp">|</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="o">[</span><span class="n">H1</span><span class="o">,</span><span class="w"> </span><span class="n">norm</span><span class="o">,</span><span class="w"> </span><span class="n">sq_abs</span><span class="o">]</span> <span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="o">(</span><span class="n">y.norm</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="o">(</span><span class="n">y.norm</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">gcongr</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">Int.abs_mod'_le</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="n">norm_y_pos</span> <span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">norm</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">norm</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">ring</span> <span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">norm</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">norm</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">gcongr</span><span class="bp">;</span><span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">Int.ediv_mul_le</span><span class="bp">;</span><span class="w"> </span><span class="n">norm_num</span> <span class="w"> </span><span class="k">calc</span><span class="w"> </span><span class="n">norm</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">%</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">norm</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">le_of_mul_le_mul_right</span><span class="w"> </span><span class="n">H2</span><span class="w"> </span><span class="n">norm_y_pos</span> <span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">norm</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">Int.ediv_lt_of_lt_mul</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">norm_num</span> <span class="w"> </span><span class="bp">·</span><span class="w"> </span><span class="n">linarith</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">norm_mod_lt</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">GaussInt</span><span class="o">)</span> <span class="o">{</span><span class="n">y</span> <span class="o">:</span> <span class="n">GaussInt</span><span class="o">}</span> <span class="o">(</span><span class="n">hy</span> <span class="o">:</span> <span class="n">y</span> <span class="bp">≠</span> <span class="mi">0</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">x</span> <span class="bp">%</span> <span class="n">y</span><span class="o">)</span><span class="bp">.</span><span class="n">norm</span> <span class="bp"><</span> <span class="n">y.norm</span> <span class="o">:=</span> <span class="kd">by</span> <span class="k">have</span> <span class="n">norm_y_pos</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp"><</span> <span class="n">norm</span> <span class="n">y</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rwa</span> <span class="o">[</span><span class="n">norm_pos</span><span class="o">]</span> <span class="k">have</span> <span class="n">H1</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">%</span> <span class="n">y</span> <span class="bp">*</span> <span class="n">conj</span> <span class="n">y</span> <span class="bp">=</span> <span class="o">⟨</span><span class="n">Int.mod'</span> <span class="o">(</span><span class="n">x</span> <span class="bp">*</span> <span class="n">conj</span> <span class="n">y</span><span class="o">)</span><span class="bp">.</span><span class="n">re</span> <span class="o">(</span><span class="n">norm</span> <span class="n">y</span><span class="o">),</span> <span class="n">Int.mod'</span> <span class="o">(</span><span class="n">x</span> <span class="bp">*</span> <span class="n">conj</span> <span class="n">y</span><span class="o">)</span><span class="bp">.</span><span class="n">im</span> <span class="o">(</span><span class="n">norm</span> <span class="n">y</span><span class="o">)⟩</span> <span class="bp">·</span> <span class="n">ext</span> <span class="bp"><;></span> <span class="n">simp</span> <span class="o">[</span><span class="n">Int.mod'_eq</span><span class="o">,</span> <span class="n">mod_def</span><span class="o">,</span> <span class="n">div_def</span><span class="o">,</span> <span class="n">norm</span><span class="o">]</span> <span class="bp"><;></span> <span class="n">ring</span> <span class="k">have</span> <span class="n">H2</span> <span class="o">:</span> <span class="n">norm</span> <span class="o">(</span><span class="n">x</span> <span class="bp">%</span> <span class="n">y</span><span class="o">)</span> <span class="bp">*</span> <span class="n">norm</span> <span class="n">y</span> <span class="bp">≤</span> <span class="n">norm</span> <span class="n">y</span> <span class="bp">/</span> <span class="mi">2</span> <span class="bp">*</span> <span class="n">norm</span> <span class="n">y</span> <span class="bp">·</span> <span class="k">calc</span> <span class="n">norm</span> <span class="o">(</span><span class="n">x</span> <span class="bp">%</span> <span class="n">y</span><span class="o">)</span> <span class="bp">*</span> <span class="n">norm</span> <span class="n">y</span> <span class="bp">=</span> <span class="n">norm</span> <span class="o">(</span><span class="n">x</span> <span class="bp">%</span> <span class="n">y</span> <span class="bp">*</span> <span class="n">conj</span> <span class="n">y</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> <span class="n">only</span> <span class="o">[</span><span class="n">norm_mul</span><span class="o">,</span> <span class="n">norm_conj</span><span class="o">]</span> <span class="n">_</span> <span class="bp">=</span> <span class="bp">|</span><span class="n">Int.mod'</span> <span class="o">(</span><span class="n">x.re</span> <span class="bp">*</span> <span class="n">y.re</span> <span class="bp">+</span> <span class="n">x.im</span> <span class="bp">*</span> <span class="n">y.im</span><span class="o">)</span> <span class="o">(</span><span class="n">norm</span> <span class="n">y</span><span class="o">)</span><span class="bp">|</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">+</span> <span class="bp">|</span><span class="n">Int.mod'</span> <span class="o">(</span><span class="bp">-</span><span class="o">(</span><span class="n">x.re</span> <span class="bp">*</span> <span class="n">y.im</span><span class="o">)</span> <span class="bp">+</span> <span class="n">x.im</span> <span class="bp">*</span> <span class="n">y.re</span><span class="o">)</span> <span class="o">(</span><span class="n">norm</span> <span class="n">y</span><span class="o">)</span><span class="bp">|</span> <span class="bp">^</span> <span class="mi">2</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> <span class="o">[</span><span class="n">H1</span><span class="o">,</span> <span class="n">norm</span><span class="o">,</span> <span class="n">sq_abs</span><span class="o">]</span> <span class="n">_</span> <span class="bp">≤</span> <span class="o">(</span><span class="n">y.norm</span> <span class="bp">/</span> <span class="mi">2</span><span class="o">)</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">+</span> <span class="o">(</span><span class="n">y.norm</span> <span class="bp">/</span> <span class="mi">2</span><span class="o">)</span> <span class="bp">^</span> <span class="mi">2</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">gcongr</span> <span class="bp"><;></span> <span class="n">apply</span> <span class="n">Int.abs_mod'_le</span> <span class="n">_</span> <span class="n">_</span> <span class="n">norm_y_pos</span> <span class="n">_</span> <span class="bp">=</span> <span class="n">norm</span> <span class="n">y</span> <span class="bp">/</span> <span class="mi">2</span> <span class="bp">*</span> <span class="o">(</span><span class="n">norm</span> <span class="n">y</span> <span class="bp">/</span> <span class="mi">2</span> <span class="bp">*</span> <span class="mi">2</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">ring</span> <span class="n">_</span> <span class="bp">≤</span> <span class="n">norm</span> <span class="n">y</span> <span class="bp">/</span> <span class="mi">2</span> <span class="bp">*</span> <span class="n">norm</span> <span class="n">y</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">gcongr</span><span class="bp">;</span> <span class="n">apply</span> <span class="n">Int.ediv_mul_le</span><span class="bp">;</span> <span class="n">norm_num</span> <span class="k">calc</span> <span class="n">norm</span> <span class="o">(</span><span class="n">x</span> <span class="bp">%</span> <span class="n">y</span><span class="o">)</span> <span class="bp">≤</span> <span class="n">norm</span> <span class="n">y</span> <span class="bp">/</span> <span class="mi">2</span> <span class="o">:=</span> <span class="n">le_of_mul_le_mul_right</span> <span class="n">H2</span> <span class="n">norm_y_pos</span> <span class="n">_</span> <span class="bp"><</span> <span class="n">norm</span> <span class="n">y</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">apply</span> <span class="n">Int.ediv_lt_of_lt_mul</span> <span class="bp">·</span> <span class="n">norm_num</span> <span class="bp">·</span> <span class="n">linarith</span> </pre></div> </div> <p>We are in the home stretch. Our <code class="docutils literal notranslate"><span class="pre">norm</span></code> function maps Gaussian integers to
-
@@ -1474,26 +1469,26 @@ numbers, and we obtain that by composing <code class="docutils literal notranslaThe first of the next two lemmas establishes that mapping the norm to the natural numbers and back to the integers does not change the value. The second one re-expresses the fact that the norm is decreasing.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">coe_natAbs_norm</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">x.norm.natAbs</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℤ</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x.norm</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Int.natAbs_of_nonneg</span><span class="w"> </span><span class="o">(</span><span class="n">norm_nonneg</span><span class="w"> </span><span class="n">_</span><span class="o">)</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">natAbs_norm_mod_lt</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hy</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">%</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="bp">.</span><span class="n">norm.natAbs</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">y.norm.natAbs</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">Int.ofNat_lt</span><span class="bp">.</span><span class="mi">1</span> <span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="n">only</span><span class="w"> </span><span class="o">[</span><span class="n">Int.natCast_natAbs</span><span class="o">,</span><span class="w"> </span><span class="n">abs_of_nonneg</span><span class="o">,</span><span class="w"> </span><span class="n">norm_nonneg</span><span class="o">]</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">norm_mod_lt</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">hy</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">coe_natAbs_norm</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">GaussInt</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">x.norm.natAbs</span> <span class="o">:</span> <span class="n">ℤ</span><span class="o">)</span> <span class="bp">=</span> <span class="n">x.norm</span> <span class="o">:=</span> <span class="n">Int.natAbs_of_nonneg</span> <span class="o">(</span><span class="n">norm_nonneg</span> <span class="n">_</span><span class="o">)</span> <span class="kd">theorem</span> <span class="n">natAbs_norm_mod_lt</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">GaussInt</span><span class="o">)</span> <span class="o">(</span><span class="n">hy</span> <span class="o">:</span> <span class="n">y</span> <span class="bp">≠</span> <span class="mi">0</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">x</span> <span class="bp">%</span> <span class="n">y</span><span class="o">)</span><span class="bp">.</span><span class="n">norm.natAbs</span> <span class="bp"><</span> <span class="n">y.norm.natAbs</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">apply</span> <span class="n">Int.ofNat_lt.1</span> <span class="n">simp</span> <span class="n">only</span> <span class="o">[</span><span class="n">Int.natCast_natAbs</span><span class="o">,</span> <span class="n">abs_of_nonneg</span><span class="o">,</span> <span class="n">norm_nonneg</span><span class="o">]</span> <span class="n">exact</span> <span class="n">norm_mod_lt</span> <span class="n">x</span> <span class="n">hy</span> </pre></div> </div> <p>We also need to establish the second key property of the norm function on a Euclidean domain.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">not_norm_mul_left_lt_norm</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="o">)</span><span class="w"> </span><span class="o">{</span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hy</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="bp">¬</span><span class="o">(</span><span class="n">norm</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y</span><span class="o">))</span><span class="bp">.</span><span class="n">natAbs</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="o">(</span><span class="n">norm</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="bp">.</span><span class="n">natAbs</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">not_lt_of_ge</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">norm_mul</span><span class="o">,</span><span class="w"> </span><span class="n">Int.natAbs_mul</span><span class="o">]</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">le_mul_of_one_le_right</span><span class="w"> </span><span class="o">(</span><span class="n">Nat.zero_le</span><span class="w"> </span><span class="n">_</span><span class="o">)</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">Int.ofNat_le</span><span class="bp">.</span><span class="mi">1</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">coe_natAbs_norm</span><span class="o">]</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">Int.add_one_le_of_lt</span><span class="w"> </span><span class="o">((</span><span class="n">norm_pos</span><span class="w"> </span><span class="n">_</span><span class="o">)</span><span class="bp">.</span><span class="n">mpr</span><span class="w"> </span><span class="n">hy</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">not_norm_mul_left_lt_norm</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">GaussInt</span><span class="o">)</span> <span class="o">{</span><span class="n">y</span> <span class="o">:</span> <span class="n">GaussInt</span><span class="o">}</span> <span class="o">(</span><span class="n">hy</span> <span class="o">:</span> <span class="n">y</span> <span class="bp">≠</span> <span class="mi">0</span><span class="o">)</span> <span class="o">:</span> <span class="bp">¬</span><span class="o">(</span><span class="n">norm</span> <span class="o">(</span><span class="n">x</span> <span class="bp">*</span> <span class="n">y</span><span class="o">))</span><span class="bp">.</span><span class="n">natAbs</span> <span class="bp"><</span> <span class="o">(</span><span class="n">norm</span> <span class="n">x</span><span class="o">)</span><span class="bp">.</span><span class="n">natAbs</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">apply</span> <span class="n">not_lt_of_ge</span> <span class="n">rw</span> <span class="o">[</span><span class="n">norm_mul</span><span class="o">,</span> <span class="n">Int.natAbs_mul</span><span class="o">]</span> <span class="n">apply</span> <span class="n">le_mul_of_one_le_right</span> <span class="o">(</span><span class="n">Nat.zero_le</span> <span class="n">_</span><span class="o">)</span> <span class="n">apply</span> <span class="n">Int.ofNat_le.1</span> <span class="n">rw</span> <span class="o">[</span><span class="n">coe_natAbs_norm</span><span class="o">]</span> <span class="n">exact</span> <span class="n">Int.add_one_le_of_lt</span> <span class="o">((</span><span class="n">norm_pos</span> <span class="n">_</span><span class="o">)</span><span class="bp">.</span><span class="n">mpr</span> <span class="n">hy</span><span class="o">)</span> </pre></div> </div> <p>We can now put it together to show that the Gaussian integers are an
-
@@ -1506,25 +1501,25 @@ Comparing the values of a norm function that returns natural numbers isjust one instance of such a measure, and in that case, the required properties are the theorems <code class="docutils literal notranslate"><span class="pre">natAbs_norm_mod_lt</span></code> and <code class="docutils literal notranslate"><span class="pre">not_norm_mul_left_lt_norm</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">EuclideanDomain</span><span class="w"> </span><span class="n">GaussInt</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">GaussInt.instCommRing</span><span class="w"> </span><span class="k">with</span> <span class="w"> </span><span class="n">quotient</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">(</span><span class="bp">·</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="bp">·</span><span class="o">)</span> <span class="w"> </span><span class="n">remainder</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">(</span><span class="bp">·</span><span class="w"> </span><span class="bp">%</span><span class="w"> </span><span class="bp">·</span><span class="o">)</span> <span class="w"> </span><span class="n">quotient_mul_add_remainder_eq</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="n">only</span><span class="bp">;</span><span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">mod_def</span><span class="o">,</span><span class="w"> </span><span class="n">add_comm</span><span class="o">]</span><span class="w"> </span><span class="bp">;</span><span class="w"> </span><span class="n">ring</span> <span class="w"> </span><span class="n">quotient_zero</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="o">[</span><span class="n">div_def</span><span class="o">,</span><span class="w"> </span><span class="n">norm</span><span class="o">,</span><span class="w"> </span><span class="n">Int.div'</span><span class="o">]</span> <span class="w"> </span><span class="n">rfl</span> <span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">(</span><span class="n">measure</span><span class="w"> </span><span class="o">(</span><span class="n">Int.natAbs</span><span class="w"> </span><span class="bp">∘</span><span class="w"> </span><span class="n">norm</span><span class="o">))</span><span class="bp">.</span><span class="mi">1</span> <span class="w"> </span><span class="n">r_wellFounded</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">(</span><span class="n">measure</span><span class="w"> </span><span class="o">(</span><span class="n">Int.natAbs</span><span class="w"> </span><span class="bp">∘</span><span class="w"> </span><span class="n">norm</span><span class="o">))</span><span class="bp">.</span><span class="mi">2</span> <span class="w"> </span><span class="n">remainder_lt</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">natAbs_norm_mod_lt</span> <span class="w"> </span><span class="n">mul_left_not_lt</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">not_norm_mul_left_lt_norm</span><span class="w"> </span><span class="o">}</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span> <span class="o">:</span> <span class="n">EuclideanDomain</span> <span class="n">GaussInt</span> <span class="o">:=</span> <span class="o">{</span> <span class="n">GaussInt.instCommRing</span> <span class="k">with</span> <span class="n">quotient</span> <span class="o">:=</span> <span class="o">(</span><span class="bp">·</span> <span class="bp">/</span> <span class="bp">·</span><span class="o">)</span> <span class="n">remainder</span> <span class="o">:=</span> <span class="o">(</span><span class="bp">·</span> <span class="bp">%</span> <span class="bp">·</span><span class="o">)</span> <span class="n">quotient_mul_add_remainder_eq</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">x</span> <span class="n">y</span> <span class="bp">↦</span> <span class="kd">by</span> <span class="n">simp</span> <span class="n">only</span><span class="bp">;</span> <span class="n">rw</span> <span class="o">[</span><span class="n">mod_def</span><span class="o">,</span> <span class="n">add_comm</span><span class="o">]</span> <span class="bp">;</span> <span class="n">ring</span> <span class="n">quotient_zero</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="kd">by</span> <span class="n">simp</span> <span class="o">[</span><span class="n">div_def</span><span class="o">,</span> <span class="n">norm</span><span class="o">,</span> <span class="n">Int.div'</span><span class="o">]</span> <span class="n">rfl</span> <span class="n">r</span> <span class="o">:=</span> <span class="o">(</span><span class="n">measure</span> <span class="o">(</span><span class="n">Int.natAbs</span> <span class="bp">∘</span> <span class="n">norm</span><span class="o">))</span><span class="bp">.</span><span class="mi">1</span> <span class="n">r_wellFounded</span> <span class="o">:=</span> <span class="o">(</span><span class="n">measure</span> <span class="o">(</span><span class="n">Int.natAbs</span> <span class="bp">∘</span> <span class="n">norm</span><span class="o">))</span><span class="bp">.</span><span class="mi">2</span> <span class="n">remainder_lt</span> <span class="o">:=</span> <span class="n">natAbs_norm_mod_lt</span> <span class="n">mul_left_not_lt</span> <span class="o">:=</span> <span class="n">not_norm_mul_left_lt_norm</span> <span class="o">}</span> </pre></div> </div> <p>An immediate payoff is that we now know that, in the Gaussian integers, the notions of being prime and being irreducible coincide.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaussInt</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Irreducible</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">Prime</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">irreducible_iff_prime</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">GaussInt</span><span class="o">)</span> <span class="o">:</span> <span class="n">Irreducible</span> <span class="n">x</span> <span class="bp">↔</span> <span class="n">Prime</span> <span class="n">x</span> <span class="o">:=</span> <span class="n">irreducible_iff_prime</span> </pre></div> </div> </section>
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-
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@@ -1,23 +1,23 @@<!DOCTYPE html> <html class="writer-html5" lang="en" data-content_root="./"> <html class="writer-html5" lang="en" > <head> <meta charset="utf-8" /><meta name="viewport" content="width=device-width, initial-scale=1" /> <meta charset="utf-8" /><meta name="generator" content="Docutils 0.17.1: http://docutils.sourceforge.net/" /> <meta name="viewport" content="width=device-width, initial-scale=1.0" /> <title>7. Hierarchies — Mathematics in Lean 0.1 documentation</title> <link rel="stylesheet" type="text/css" href="_static/pygments.css?v=80d5e7a1" /> <link rel="stylesheet" type="text/css" href="_static/css/theme.css?v=e59714d7" /> <link rel="stylesheet" type="text/css" href="_static/css/custom.css?v=0731ccc3" /> <link rel="stylesheet" href="_static/pygments.css" type="text/css" /> <link rel="stylesheet" href="_static/css/theme.css" type="text/css" /> <link rel="stylesheet" href="_static/css/custom.css" type="text/css" /> <link rel="shortcut icon" href="_static/favicon.ico"/> <script src="_static/jquery.js?v=5d32c60e"></script> <script src="_static/_sphinx_javascript_frameworks_compat.js?v=2cd50e6c"></script> <script src="_static/documentation_options.js?v=2709fde1"></script> <script src="_static/doctools.js?v=9bcbadda"></script> <script src="_static/sphinx_highlight.js?v=dc90522c"></script> <!--[if lt IE 9]> <script src="_static/js/html5shiv.min.js"></script> <![endif]--> <script data-url_root="./" id="documentation_options" src="_static/documentation_options.js"></script> <script src="_static/jquery.js"></script> <script src="_static/underscore.js"></script> <script src="_static/_sphinx_javascript_frameworks_compat.js"></script> <script src="_static/doctools.js"></script> <script src="_static/js/theme.js"></script> <link rel="index" title="Index" href="genindex.html" /> <link rel="search" title="Search" href="search.html" />
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@@ -30,15 +30,11 @@<nav data-toggle="wy-nav-shift" class="wy-nav-side"> <div class="wy-side-scroll"> <div class="wy-side-nav-search" > <a href="index.html" class="icon icon-home"> Mathematics in Lean <a href="index.html" class="icon icon-home"> Mathematics in Lean </a> <div role="search"> <form id="rtd-search-form" class="wy-form" action="search.html" method="get"> <input type="text" name="q" placeholder="Search docs" aria-label="Search docs" /> <input type="text" name="q" placeholder="Search docs" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form>
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@@ -80,8 +76,8 @@<div class="rst-content"> <div role="navigation" aria-label="Page navigation"> <ul class="wy-breadcrumbs"> <li><a href="index.html" class="icon icon-home" aria-label="Home"></a></li> <li class="breadcrumb-item active"><span class="section-number">7. </span>Hierarchies</li> <li><a href="index.html" class="icon icon-home"></a> »</li> <li><span class="section-number">7. </span>Hierarchies</li> <li class="wy-breadcrumbs-aside"> <a href="_sources/C07_Hierarchies.rst.txt" rel="nofollow"> View page source</a> </li>
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@@ -92,7 +88,7 @@<div itemprop="articleBody"> <section id="hierarchies"> <span id="id1"></span><h1><span class="section-number">7. </span>Hierarchies<a class="headerlink" href="#hierarchies" title="Link to this heading"></a></h1> <span id="id1"></span><h1><span class="section-number">7. </span>Hierarchies<a class="headerlink" href="#hierarchies" title="Permalink to this heading"></a></h1> <p>We have seen in <a class="reference internal" href="C06_Structures.html#structures"><span class="std std-numref">Chapter 6</span></a> how to define the class of groups and build instances of this class, and then how to build an instance of the commutative ring class. But of course there is a hierarchy here: a
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@@ -109,13 +105,13 @@ so we will used indices to distinguish our version. For instance we will have <cas our version of <code class="docutils literal notranslate"><span class="pre">Ring</span></code>. Since we will gradually explain more powerful ways of formalizing structures, those indices will sometimes grow beyond one.</p> <section id="basics"> <span id="section-hierarchies-basics"></span><h2><span class="section-number">7.1. </span>Basics<a class="headerlink" href="#basics" title="Link to this heading"></a></h2> <span id="section-hierarchies-basics"></span><h2><span class="section-number">7.1. </span>Basics<a class="headerlink" href="#basics" title="Permalink to this heading"></a></h2> <p>At the very bottom of all hierarchies in Lean, we find data-carrying classes. The following class records that the given type <code class="docutils literal notranslate"><span class="pre">α</span></code> is endowed with a distinguished element called <code class="docutils literal notranslate"><span class="pre">one</span></code>. At this stage, it has no property at all.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span><span class="w"> </span><span class="n">One₁</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="sd">/-- The element one -/</span> <span class="w"> </span><span class="n">one</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span> <span class="n">One₁</span> <span class="o">(</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="n">where</span> <span class="sd">/-- The element one -/</span> <span class="n">one</span> <span class="o">:</span> <span class="n">α</span> </pre></div> </div> <p>Since we’ll make a much heavier use of classes in this chapter, we need to understand some
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@@ -127,18 +123,18 @@ as long as they are marked as instance-implicit, i.e. appear between square bracThose two effects could also have been achieved using the <code class="docutils literal notranslate"><span class="pre">structure</span></code> command with <code class="docutils literal notranslate"><span class="pre">class</span></code> attribute, i.e. writing <code class="docutils literal notranslate"><span class="pre">@[class]</span> <span class="pre">structure</span></code> instance of <code class="docutils literal notranslate"><span class="pre">class</span></code>. But the class command also ensures that <code class="docutils literal notranslate"><span class="pre">One₁</span> <span class="pre">α</span></code> appears as an instance-implicit argument in its own fields. Compare:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="n">One₁.one</span><span class="w"> </span><span class="c1">-- One₁.one {α : Type} [self : One₁ α] : α</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="n">One₁.one</span> <span class="c1">-- One₁.one {α : Type} [self : One₁ α] : α</span> <span class="kd">@[</span><span class="n">class</span><span class="kd">]</span><span class="w"> </span><span class="kd">structure</span><span class="w"> </span><span class="n">One₂</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="sd">/-- The element one -/</span> <span class="w"> </span><span class="n">one</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span> <span class="kd">@[class]</span> <span class="kd">structure</span> <span class="n">One₂</span> <span class="o">(</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="n">where</span> <span class="sd">/-- The element one -/</span> <span class="n">one</span> <span class="o">:</span> <span class="n">α</span> <span class="k">#check</span><span class="w"> </span><span class="n">One₂.one</span> <span class="k">#check</span> <span class="n">One₂.one</span> </pre></div> </div> <p>In the second check, we can see that <code class="docutils literal notranslate"><span class="pre">self</span> <span class="pre">:</span> <span class="pre">One₂</span> <span class="pre">α</span></code> is an explicit argument. Let us make sure the first version is indeed usable without any explicit argument.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">One₁</span><span class="w"> </span><span class="n">α</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">One₁.one</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="o">[</span><span class="n">One₁</span> <span class="n">α</span><span class="o">]</span> <span class="o">:</span> <span class="n">α</span> <span class="o">:=</span> <span class="n">One₁.one</span> </pre></div> </div> <p>Remark: in the above example, the argument <code class="docutils literal notranslate"><span class="pre">One₁</span> <span class="pre">α</span></code> is marked as instance-implicit,
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@@ -152,7 +148,7 @@ example, leaving out the type ascription <code class="docutils literal notranslawhere <code class="docutils literal notranslate"><span class="pre">?m.263</span> <span class="pre">α</span></code> means “some type depending on <code class="docutils literal notranslate"><span class="pre">α</span></code>” (and 263 is simply an auto-generated index that would be useful to distinguish between several unknown things). Another way to avoid this issue would be to use a type annotation, as in:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">One₁</span><span class="w"> </span><span class="n">α</span><span class="o">]</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">(</span><span class="n">One₁.one</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="o">[</span><span class="n">One₁</span> <span class="n">α</span><span class="o">]</span> <span class="o">:=</span> <span class="o">(</span><span class="n">One₁.one</span> <span class="o">:</span> <span class="n">α</span><span class="o">)</span> </pre></div> </div> <p>You may have already encountered that issue when playing with limits of sequences
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@@ -163,30 +159,30 @@ or real numbers.</p>with the builtin notation for <code class="docutils literal notranslate"><span class="pre">1</span></code>, we will use <code class="docutils literal notranslate"><span class="pre">𝟙</span></code>. This is achieved by the following command where the first line tells Lean to use the documentation of <code class="docutils literal notranslate"><span class="pre">One₁.one</span></code> as documentation for the symbol <code class="docutils literal notranslate"><span class="pre">𝟙</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">@[</span><span class="n">inherit_doc</span><span class="kd">]</span> <span class="kd">notation</span><span class="w"> </span><span class="s2">"𝟙"</span><span class="w"> </span><span class="bp">=></span><span class="w"> </span><span class="n">One₁.one</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">@[inherit_doc]</span> <span class="kd">notation</span> <span class="s2">"𝟙"</span> <span class="bp">=></span> <span class="n">One₁.one</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">One₁</span><span class="w"> </span><span class="n">α</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="mi">𝟙</span> <span class="kd">example</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">}</span> <span class="o">[</span><span class="n">One₁</span> <span class="n">α</span><span class="o">]</span> <span class="o">:</span> <span class="n">α</span> <span class="o">:=</span> <span class="mi">𝟙</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">One₁</span><span class="w"> </span><span class="n">α</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="mi">𝟙</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">𝟙</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">rfl</span> <span class="kd">example</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">}</span> <span class="o">[</span><span class="n">One₁</span> <span class="n">α</span><span class="o">]</span> <span class="o">:</span> <span class="o">(</span><span class="mi">𝟙</span> <span class="o">:</span> <span class="n">α</span><span class="o">)</span> <span class="bp">=</span> <span class="mi">𝟙</span> <span class="o">:=</span> <span class="n">rfl</span> </pre></div> </div> <p>We now want a data-carrying class recording a binary operation. We don’t want to choose between addition and multiplication for now so we’ll use diamond.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span><span class="w"> </span><span class="n">Dia₁</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">dia</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">α</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span> <span class="n">Dia₁</span> <span class="o">(</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="n">where</span> <span class="n">dia</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">α</span> <span class="kd">infixl</span><span class="o">:</span><span class="mi">70</span><span class="w"> </span><span class="s2">" ⋄ "</span><span class="w"> </span><span class="bp">=></span><span class="w"> </span><span class="n">Dia₁.dia</span> <span class="kd">infixl</span><span class="o">:</span><span class="mi">70</span> <span class="s2">" ⋄ "</span> <span class="bp">=></span> <span class="n">Dia₁.dia</span> </pre></div> </div> <p>As in the <code class="docutils literal notranslate"><span class="pre">One₁</span></code> example, the operation has no property at all at this stage. Let us now define the class of semigroup structures where the operation is denoted by <code class="docutils literal notranslate"><span class="pre">⋄</span></code>. For now, we define it by hand as a structure with two fields, a <code class="docutils literal notranslate"><span class="pre">Dia₁</span></code> instance and some <code class="docutils literal notranslate"><span class="pre">Prop</span></code>-valued field <code class="docutils literal notranslate"><span class="pre">dia_assoc</span></code> asserting associativity of <code class="docutils literal notranslate"><span class="pre">⋄</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span><span class="w"> </span><span class="n">Semigroup₁</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">toDia₁</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Dia₁</span><span class="w"> </span><span class="n">α</span> <span class="w"> </span><span class="sd">/-- Diamond is associative -/</span> <span class="w"> </span><span class="n">dia_assoc</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">⋄</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">⋄</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">⋄</span><span class="w"> </span><span class="o">(</span><span class="n">b</span><span class="w"> </span><span class="bp">⋄</span><span class="w"> </span><span class="n">c</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span> <span class="n">Semigroup₁</span> <span class="o">(</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="n">where</span> <span class="n">toDia₁</span> <span class="o">:</span> <span class="n">Dia₁</span> <span class="n">α</span> <span class="sd">/-- Diamond is associative -/</span> <span class="n">dia_assoc</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">α</span><span class="o">,</span> <span class="n">a</span> <span class="bp">⋄</span> <span class="n">b</span> <span class="bp">⋄</span> <span class="n">c</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">⋄</span> <span class="o">(</span><span class="n">b</span> <span class="bp">⋄</span> <span class="n">c</span><span class="o">)</span> </pre></div> </div> <p>Note that while stating <cite>dia_assoc</cite>, the previously defined field <cite>toDia₁</cite> is in the local
-
@@ -195,19 +191,19 @@ of <cite>a ⋄ b</cite>. However this <cite>toDia₁</cite> field does nHence doing <code class="docutils literal notranslate"><span class="pre">example</span> <span class="pre">{α</span> <span class="pre">:</span> <span class="pre">Type}</span> <span class="pre">[Semigroup₁</span> <span class="pre">α]</span> <span class="pre">(a</span> <span class="pre">b</span> <span class="pre">:</span> <span class="pre">α)</span> <span class="pre">:</span> <span class="pre">α</span> <span class="pre">:=</span> <span class="pre">a</span> <span class="pre">⋄</span> <span class="pre">b</span></code> would fail with error message <code class="docutils literal notranslate"><span class="pre">failed</span> <span class="pre">to</span> <span class="pre">synthesize</span> <span class="pre">instance</span> <span class="pre">Dia₁</span> <span class="pre">α</span></code>.</p> <p>We can fix this by adding the <code class="docutils literal notranslate"><span class="pre">instance</span></code> attribute later.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">attribute</span><span class="w"> </span><span class="o">[</span><span class="kd">instance</span><span class="o">]</span><span class="w"> </span><span class="n">Semigroup₁.toDia₁</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">attribute</span> <span class="o">[</span><span class="kd">instance</span><span class="o">]</span> <span class="n">Semigroup₁.toDia₁</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Semigroup₁</span><span class="w"> </span><span class="n">α</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">⋄</span><span class="w"> </span><span class="n">b</span> <span class="kd">example</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">}</span> <span class="o">[</span><span class="n">Semigroup₁</span> <span class="n">α</span><span class="o">]</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">α</span><span class="o">)</span> <span class="o">:</span> <span class="n">α</span> <span class="o">:=</span> <span class="n">a</span> <span class="bp">⋄</span> <span class="n">b</span> </pre></div> </div> <p>Before building up, we need a more convenient way to extend structures than explicitly writing fields like <cite>toDia₁</cite> and adding the instance attribute by hand. The <code class="docutils literal notranslate"><span class="pre">class</span></code> supports this using the <code class="docutils literal notranslate"><span class="pre">extends</span></code> syntax as in:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span><span class="w"> </span><span class="n">Semigroup₂</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="kd">extends</span><span class="w"> </span><span class="n">Dia₁</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="sd">/-- Diamond is associative -/</span> <span class="w"> </span><span class="n">dia_assoc</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">⋄</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">⋄</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">⋄</span><span class="w"> </span><span class="o">(</span><span class="n">b</span><span class="w"> </span><span class="bp">⋄</span><span class="w"> </span><span class="n">c</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span> <span class="n">Semigroup₂</span> <span class="o">(</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="kd">extends</span> <span class="n">Dia₁</span> <span class="n">α</span> <span class="n">where</span> <span class="sd">/-- Diamond is associative -/</span> <span class="n">dia_assoc</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">α</span><span class="o">,</span> <span class="n">a</span> <span class="bp">⋄</span> <span class="n">b</span> <span class="bp">⋄</span> <span class="n">c</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">⋄</span> <span class="o">(</span><span class="n">b</span> <span class="bp">⋄</span> <span class="n">c</span><span class="o">)</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Semigroup₂</span><span class="w"> </span><span class="n">α</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">⋄</span><span class="w"> </span><span class="n">b</span> <span class="kd">example</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">}</span> <span class="o">[</span><span class="n">Semigroup₂</span> <span class="n">α</span><span class="o">]</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">α</span><span class="o">)</span> <span class="o">:</span> <span class="n">α</span> <span class="o">:=</span> <span class="n">a</span> <span class="bp">⋄</span> <span class="n">b</span> </pre></div> </div> <p>Note this syntax is also available in the <code class="docutils literal notranslate"><span class="pre">structure</span></code> command, although it that
-
@@ -215,11 +211,11 @@ case it fixes only the hurdle of writing fields such as <cite>toDia₁</citeis no instance to define in that case.</p> <p>Let us now try to combine a diamond operation and a distinguished one with axioms saying this element is neutral on both sides.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span><span class="w"> </span><span class="n">DiaOneClass₁</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="kd">extends</span><span class="w"> </span><span class="n">One₁</span><span class="w"> </span><span class="n">α</span><span class="o">,</span><span class="w"> </span><span class="n">Dia₁</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="sd">/-- One is a left neutral element for diamond. -/</span> <span class="w"> </span><span class="n">one_dia</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">,</span><span class="w"> </span><span class="mi">𝟙</span><span class="w"> </span><span class="bp">⋄</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span> <span class="w"> </span><span class="sd">/-- One is a right neutral element for diamond -/</span> <span class="w"> </span><span class="n">dia_one</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">⋄</span><span class="w"> </span><span class="mi">𝟙</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span> <span class="n">DiaOneClass₁</span> <span class="o">(</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="kd">extends</span> <span class="n">One₁</span> <span class="n">α</span><span class="o">,</span> <span class="n">Dia₁</span> <span class="n">α</span> <span class="n">where</span> <span class="sd">/-- One is a left neutral element for diamond. -/</span> <span class="n">one_dia</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span> <span class="o">:</span> <span class="n">α</span><span class="o">,</span> <span class="mi">𝟙</span> <span class="bp">⋄</span> <span class="n">a</span> <span class="bp">=</span> <span class="n">a</span> <span class="sd">/-- One is a right neutral element for diamond -/</span> <span class="n">dia_one</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span> <span class="o">:</span> <span class="n">α</span><span class="o">,</span> <span class="n">a</span> <span class="bp">⋄</span> <span class="mi">𝟙</span> <span class="bp">=</span> <span class="n">a</span> </pre></div> </div> <p>In the next example, we tell Lean that <code class="docutils literal notranslate"><span class="pre">α</span></code> has a <code class="docutils literal notranslate"><span class="pre">DiaOneClass₁</span></code> structure and state a
-
@@ -229,13 +225,13 @@ is rather terse by default but it can be expanded by clicking on lines ending wiIt includes failed attempts where Lean tried to find instances before having enough type information to succeed. The successful attempts do involve the instances generated by the <code class="docutils literal notranslate"><span class="pre">extends</span></code> syntax.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">set_option</span><span class="w"> </span><span class="n">trace.Meta.synthInstance</span><span class="w"> </span><span class="n">true</span><span class="w"> </span><span class="k">in</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">DiaOneClass₁</span><span class="w"> </span><span class="n">α</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Prop</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">⋄</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">𝟙</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">set_option</span> <span class="n">trace.Meta.synthInstance</span> <span class="n">true</span> <span class="k">in</span> <span class="kd">example</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">}</span> <span class="o">[</span><span class="n">DiaOneClass₁</span> <span class="n">α</span><span class="o">]</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">α</span><span class="o">)</span> <span class="o">:</span> <span class="kt">Prop</span> <span class="o">:=</span> <span class="n">a</span> <span class="bp">⋄</span> <span class="n">b</span> <span class="bp">=</span> <span class="mi">𝟙</span> </pre></div> </div> <p>Note that we don’t need to include extra fields where combining existing classes. Hence we can define monoids as:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span><span class="w"> </span><span class="n">Monoid₁</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="kd">extends</span><span class="w"> </span><span class="n">Semigroup₁</span><span class="w"> </span><span class="n">α</span><span class="o">,</span><span class="w"> </span><span class="n">DiaOneClass₁</span><span class="w"> </span><span class="n">α</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span> <span class="n">Monoid₁</span> <span class="o">(</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="kd">extends</span> <span class="n">Semigroup₁</span> <span class="n">α</span><span class="o">,</span> <span class="n">DiaOneClass₁</span> <span class="n">α</span> </pre></div> </div> <p>While the above definition seems straightforward, it hides an important subtlety. Both
-
@@ -243,25 +239,25 @@ define monoids as:</p>a <code class="docutils literal notranslate"><span class="pre">Monoid₁</span> <span class="pre">α</span></code> instance gives two unrelated diamond operations on <code class="docutils literal notranslate"><span class="pre">α</span></code>, one coming from a field <code class="docutils literal notranslate"><span class="pre">Monoid₁.toSemigroup₁</span></code> and one coming from a field <code class="docutils literal notranslate"><span class="pre">Monoid₁.toDiaOneClass₁</span></code>.</p> <p>Indeed if we try to build a monoid class by hand using:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span><span class="w"> </span><span class="n">Monoid₂</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">toSemigroup₁</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Semigroup₁</span><span class="w"> </span><span class="n">α</span> <span class="w"> </span><span class="n">toDiaOneClass₁</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">DiaOneClass₁</span><span class="w"> </span><span class="n">α</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span> <span class="n">Monoid₂</span> <span class="o">(</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="n">where</span> <span class="n">toSemigroup₁</span> <span class="o">:</span> <span class="n">Semigroup₁</span> <span class="n">α</span> <span class="n">toDiaOneClass₁</span> <span class="o">:</span> <span class="n">DiaOneClass₁</span> <span class="n">α</span> </pre></div> </div> <p>then we get two completely unrelated diamond operations <code class="docutils literal notranslate"><span class="pre">Monoid₂.toSemigroup₁.toDia₁.dia</span></code> and <code class="docutils literal notranslate"><span class="pre">Monoid₂.toDiaOneClass₁.toDia₁.dia</span></code>.</p> <p>The version generated using the <code class="docutils literal notranslate"><span class="pre">extends</span></code> syntax does not have this defect.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid₁</span><span class="w"> </span><span class="n">α</span><span class="o">]</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="o">(</span><span class="n">Monoid₁.toSemigroup₁.toDia₁.dia</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">α</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">Monoid₁.toDiaOneClass₁.toDia₁.dia</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">rfl</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">}</span> <span class="o">[</span><span class="n">Monoid₁</span> <span class="n">α</span><span class="o">]</span> <span class="o">:</span> <span class="o">(</span><span class="n">Monoid₁.toSemigroup₁.toDia₁.dia</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">α</span><span class="o">)</span> <span class="bp">=</span> <span class="n">Monoid₁.toDiaOneClass₁.toDia₁.dia</span> <span class="o">:=</span> <span class="n">rfl</span> </pre></div> </div> <p>So the <code class="docutils literal notranslate"><span class="pre">class</span></code> command did some magic for us (and the <code class="docutils literal notranslate"><span class="pre">structure</span></code> command would have done it too). An easy way to see what are the fields of our classes is to check their constructor. Compare:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="c">/-</span><span class="cm"> Monoid₂.mk {α : Type} (toSemigroup₁ : Semigroup₁ α) (toDiaOneClass₁ : DiaOneClass₁ α) : Monoid₂ α -/</span> <span class="k">#check</span><span class="w"> </span><span class="n">Monoid₂.mk</span> <span class="k">#check</span> <span class="n">Monoid₂.mk</span> <span class="c">/-</span><span class="cm"> Monoid₁.mk {α : Type} [toSemigroup₁ : Semigroup₁ α] [toOne₁ : One₁ α] (one_dia : ∀ (a : α), 𝟙 ⋄ a = a) (dia_one : ∀ (a : α), a ⋄ 𝟙 = a) : Monoid₁ α -/</span> <span class="k">#check</span><span class="w"> </span><span class="n">Monoid₁.mk</span> <span class="k">#check</span> <span class="n">Monoid₁.mk</span> </pre></div> </div> <p>So we see that <code class="docutils literal notranslate"><span class="pre">Monoid₁</span></code> takes <code class="docutils literal notranslate"><span class="pre">Semigroup₁</span> <span class="pre">α</span></code> argument as expected but then it won’t
-
@@ -269,50 +265,50 @@ take a would-be overlapping <code class="docutils literal notranslate"><span claonly the non-overlapping parts. And it also auto-generated an instance <code class="docutils literal notranslate"><span class="pre">Monoid₁.toDiaOneClass₁</span></code> which is <em>not</em> a field but has the expected signature which, from the end-user point of view, restores the symmetry between the two extended classes <code class="docutils literal notranslate"><span class="pre">Semigroup₁</span></code> and <code class="docutils literal notranslate"><span class="pre">DiaOneClass₁</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="n">Monoid₁.toSemigroup₁</span> <span class="k">#check</span><span class="w"> </span><span class="n">Monoid₁.toDiaOneClass₁</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="n">Monoid₁.toSemigroup₁</span> <span class="k">#check</span> <span class="n">Monoid₁.toDiaOneClass₁</span> </pre></div> </div> <p>We are now very close to defining groups. We could add to the monoid structure a field asserting the existence of an inverse for every element. But then we would need to work to access these inverses. In practice it is more convenient to add it as data. To optimize reusability, we define a new data-carrying class, and then give it some notation.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span><span class="w"> </span><span class="n">Inv₁</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="sd">/-- The inversion function -/</span> <span class="w"> </span><span class="n">inv</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">α</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span> <span class="n">Inv₁</span> <span class="o">(</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="n">where</span> <span class="sd">/-- The inversion function -/</span> <span class="n">inv</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">α</span> <span class="kd">@[</span><span class="n">inherit_doc</span><span class="kd">]</span> <span class="kd">postfix</span><span class="o">:</span><span class="n">max</span><span class="w"> </span><span class="s2">"⁻¹"</span><span class="w"> </span><span class="bp">=></span><span class="w"> </span><span class="n">Inv₁.inv</span> <span class="kd">@[inherit_doc]</span> <span class="kd">postfix</span><span class="o">:</span><span class="n">max</span> <span class="s2">"⁻¹"</span> <span class="bp">=></span> <span class="n">Inv₁.inv</span> <span class="kd">class</span><span class="w"> </span><span class="n">Group₁</span><span class="w"> </span><span class="o">(</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="kd">extends</span><span class="w"> </span><span class="n">Monoid₁</span><span class="w"> </span><span class="n">G</span><span class="o">,</span><span class="w"> </span><span class="n">Inv₁</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">inv_dia</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="bp">⁻¹</span><span class="w"> </span><span class="bp">⋄</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">𝟙</span> <span class="kd">class</span> <span class="n">Group₁</span> <span class="o">(</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="kd">extends</span> <span class="n">Monoid₁</span> <span class="n">G</span><span class="o">,</span> <span class="n">Inv₁</span> <span class="n">G</span> <span class="n">where</span> <span class="n">inv_dia</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span> <span class="o">:</span> <span class="n">G</span><span class="o">,</span> <span class="n">a</span><span class="bp">⁻¹</span> <span class="bp">⋄</span> <span class="n">a</span> <span class="bp">=</span> <span class="mi">𝟙</span> </pre></div> </div> <p>The above definition may seem too weak, we only ask that <code class="docutils literal notranslate"><span class="pre">a⁻¹</span></code> is a left-inverse of <code class="docutils literal notranslate"><span class="pre">a</span></code>. But the other side is automatic. In order to prove that, we need a preliminary lemma.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">lemma</span><span class="w"> </span><span class="n">left_inv_eq_right_inv₁</span><span class="w"> </span><span class="o">{</span><span class="n">M</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid₁</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">M</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hba</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">⋄</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">𝟙</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hac</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">⋄</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">𝟙</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="bp">←</span><span class="w"> </span><span class="n">DiaOneClass₁.one_dia</span><span class="w"> </span><span class="n">c</span><span class="o">,</span><span class="w"> </span><span class="bp">←</span><span class="w"> </span><span class="n">hba</span><span class="o">,</span><span class="w"> </span><span class="n">Semigroup₁.dia_assoc</span><span class="o">,</span><span class="w"> </span><span class="n">hac</span><span class="o">,</span><span class="w"> </span><span class="n">DiaOneClass₁.dia_one</span><span class="w"> </span><span class="n">b</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">lemma</span> <span class="n">left_inv_eq_right_inv₁</span> <span class="o">{</span><span class="n">M</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">}</span> <span class="o">[</span><span class="n">Monoid₁</span> <span class="n">M</span><span class="o">]</span> <span class="o">{</span><span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">M</span><span class="o">}</span> <span class="o">(</span><span class="n">hba</span> <span class="o">:</span> <span class="n">b</span> <span class="bp">⋄</span> <span class="n">a</span> <span class="bp">=</span> <span class="mi">𝟙</span><span class="o">)</span> <span class="o">(</span><span class="n">hac</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">⋄</span> <span class="n">c</span> <span class="bp">=</span> <span class="mi">𝟙</span><span class="o">)</span> <span class="o">:</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">c</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="bp">←</span> <span class="n">DiaOneClass₁.one_dia</span> <span class="n">c</span><span class="o">,</span> <span class="bp">←</span> <span class="n">hba</span><span class="o">,</span> <span class="n">Semigroup₁.dia_assoc</span><span class="o">,</span> <span class="n">hac</span><span class="o">,</span> <span class="n">DiaOneClass₁.dia_one</span> <span class="n">b</span><span class="o">]</span> </pre></div> </div> <p>In this lemma, it is pretty annoying to give full names, especially since it requires knowing which part of the hierarchy provides those facts. One way to fix this is to use the <code class="docutils literal notranslate"><span class="pre">export</span></code> command to copy those facts as lemmas in the root name space.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">export</span><span class="w"> </span><span class="n">DiaOneClass₁</span><span class="w"> </span><span class="o">(</span><span class="n">one_dia</span><span class="w"> </span><span class="n">dia_one</span><span class="o">)</span> <span class="kn">export</span><span class="w"> </span><span class="n">Semigroup₁</span><span class="w"> </span><span class="o">(</span><span class="n">dia_assoc</span><span class="o">)</span> <span class="kn">export</span><span class="w"> </span><span class="n">Group₁</span><span class="w"> </span><span class="o">(</span><span class="n">inv_dia</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">export</span> <span class="n">DiaOneClass₁</span> <span class="o">(</span><span class="n">one_dia</span> <span class="n">dia_one</span><span class="o">)</span> <span class="kn">export</span> <span class="n">Semigroup₁</span> <span class="o">(</span><span class="n">dia_assoc</span><span class="o">)</span> <span class="kn">export</span> <span class="n">Group₁</span> <span class="o">(</span><span class="n">inv_dia</span><span class="o">)</span> </pre></div> </div> <p>We can then rewrite the above proof as:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">M</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid₁</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">M</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hba</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">⋄</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">𝟙</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hac</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">⋄</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">𝟙</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="bp">←</span><span class="w"> </span><span class="n">one_dia</span><span class="w"> </span><span class="n">c</span><span class="o">,</span><span class="w"> </span><span class="bp">←</span><span class="w"> </span><span class="n">hba</span><span class="o">,</span><span class="w"> </span><span class="n">dia_assoc</span><span class="o">,</span><span class="w"> </span><span class="n">hac</span><span class="o">,</span><span class="w"> </span><span class="n">dia_one</span><span class="w"> </span><span class="n">b</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">M</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">}</span> <span class="o">[</span><span class="n">Monoid₁</span> <span class="n">M</span><span class="o">]</span> <span class="o">{</span><span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">M</span><span class="o">}</span> <span class="o">(</span><span class="n">hba</span> <span class="o">:</span> <span class="n">b</span> <span class="bp">⋄</span> <span class="n">a</span> <span class="bp">=</span> <span class="mi">𝟙</span><span class="o">)</span> <span class="o">(</span><span class="n">hac</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">⋄</span> <span class="n">c</span> <span class="bp">=</span> <span class="mi">𝟙</span><span class="o">)</span> <span class="o">:</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">c</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="bp">←</span> <span class="n">one_dia</span> <span class="n">c</span><span class="o">,</span> <span class="bp">←</span> <span class="n">hba</span><span class="o">,</span> <span class="n">dia_assoc</span><span class="o">,</span> <span class="n">hac</span><span class="o">,</span> <span class="n">dia_one</span> <span class="n">b</span><span class="o">]</span> </pre></div> </div> <p>It is now your turn to prove things about our algebraic structures.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">lemma</span><span class="w"> </span><span class="n">inv_eq_of_dia</span><span class="w"> </span><span class="o">[</span><span class="n">Group₁</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">⋄</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">𝟙</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="bp">⁻¹</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">lemma</span> <span class="n">inv_eq_of_dia</span> <span class="o">[</span><span class="n">Group₁</span> <span class="n">G</span><span class="o">]</span> <span class="o">{</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">G</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">⋄</span> <span class="n">b</span> <span class="bp">=</span> <span class="mi">𝟙</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span><span class="bp">⁻¹</span> <span class="bp">=</span> <span class="n">b</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="kd">lemma</span><span class="w"> </span><span class="n">dia_inv</span><span class="w"> </span><span class="o">[</span><span class="n">Group₁</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">⋄</span><span class="w"> </span><span class="n">a</span><span class="bp">⁻¹</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">𝟙</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">lemma</span> <span class="n">dia_inv</span> <span class="o">[</span><span class="n">Group₁</span> <span class="n">G</span><span class="o">]</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">G</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">⋄</span> <span class="n">a</span><span class="bp">⁻¹</span> <span class="bp">=</span> <span class="mi">𝟙</span> <span class="o">:=</span> <span class="gr">sorry</span> </pre></div> </div> <p>At this stage we would like to move on to define rings, but there is a serious issue.
-
@@ -330,84 +326,84 @@ lemmas are then only stated in multiplicative notation and marked with the attrito generate the additive version as <code class="docutils literal notranslate"><span class="pre">left_inv_eq_right_inv'</span></code> with its auto-generated additive version <code class="docutils literal notranslate"><span class="pre">left_neg_eq_right_neg'</span></code>. In order to check the name of this additive version we used the <code class="docutils literal notranslate"><span class="pre">whatsnew</span> <span class="pre">in</span></code> command on top of <code class="docutils literal notranslate"><span class="pre">left_inv_eq_right_inv'</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span><span class="w"> </span><span class="n">AddSemigroup₃</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="kd">extends</span><span class="w"> </span><span class="n">Add</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="n">where</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span> <span class="n">AddSemigroup₃</span> <span class="o">(</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="kd">extends</span> <span class="n">Add</span> <span class="n">α</span> <span class="n">where</span> <span class="sd">/-- Addition is associative -/</span> <span class="w"> </span><span class="n">add_assoc₃</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="o">(</span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">c</span><span class="o">)</span> <span class="n">add_assoc₃</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">α</span><span class="o">,</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">+</span> <span class="n">c</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">+</span> <span class="o">(</span><span class="n">b</span> <span class="bp">+</span> <span class="n">c</span><span class="o">)</span> <span class="kd">@[</span><span class="n">to_additive</span><span class="w"> </span><span class="n">AddSemigroup₃</span><span class="kd">]</span> <span class="kd">class</span><span class="w"> </span><span class="n">Semigroup₃</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="kd">extends</span><span class="w"> </span><span class="n">Mul</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="n">where</span> <span class="kd">@[to_additive AddSemigroup₃]</span> <span class="kd">class</span> <span class="n">Semigroup₃</span> <span class="o">(</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="kd">extends</span> <span class="n">Mul</span> <span class="n">α</span> <span class="n">where</span> <span class="sd">/-- Multiplication is associative -/</span> <span class="w"> </span><span class="n">mul_assoc₃</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="o">)</span> <span class="n">mul_assoc₃</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">α</span><span class="o">,</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">c</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">*</span> <span class="o">(</span><span class="n">b</span> <span class="bp">*</span> <span class="n">c</span><span class="o">)</span> <span class="kd">class</span><span class="w"> </span><span class="n">AddMonoid₃</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="kd">extends</span><span class="w"> </span><span class="n">AddSemigroup₃</span><span class="w"> </span><span class="n">α</span><span class="o">,</span><span class="w"> </span><span class="n">AddZeroClass</span><span class="w"> </span><span class="n">α</span> <span class="kd">class</span> <span class="n">AddMonoid₃</span> <span class="o">(</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="kd">extends</span> <span class="n">AddSemigroup₃</span> <span class="n">α</span><span class="o">,</span> <span class="n">AddZeroClass</span> <span class="n">α</span> <span class="kd">@[</span><span class="n">to_additive</span><span class="w"> </span><span class="n">AddMonoid₃</span><span class="kd">]</span> <span class="kd">class</span><span class="w"> </span><span class="n">Monoid₃</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="kd">extends</span><span class="w"> </span><span class="n">Semigroup₃</span><span class="w"> </span><span class="n">α</span><span class="o">,</span><span class="w"> </span><span class="n">MulOneClass</span><span class="w"> </span><span class="n">α</span> <span class="kd">@[to_additive AddMonoid₃]</span> <span class="kd">class</span> <span class="n">Monoid₃</span> <span class="o">(</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="kd">extends</span> <span class="n">Semigroup₃</span> <span class="n">α</span><span class="o">,</span> <span class="n">MulOneClass</span> <span class="n">α</span> <span class="kn">attribute</span><span class="w"> </span><span class="o">[</span><span class="n">to_additive</span><span class="w"> </span><span class="n">existing</span><span class="o">]</span><span class="w"> </span><span class="n">Monoid₃.toMulOneClass</span> <span class="kn">attribute</span> <span class="o">[</span><span class="n">to_additive</span> <span class="n">existing</span><span class="o">]</span> <span class="n">Monoid₃.toMulOneClass</span> <span class="kn">export</span><span class="w"> </span><span class="n">Semigroup₃</span><span class="w"> </span><span class="o">(</span><span class="n">mul_assoc₃</span><span class="o">)</span> <span class="kn">export</span><span class="w"> </span><span class="n">AddSemigroup₃</span><span class="w"> </span><span class="o">(</span><span class="n">add_assoc₃</span><span class="o">)</span> <span class="kn">export</span> <span class="n">Semigroup₃</span> <span class="o">(</span><span class="n">mul_assoc₃</span><span class="o">)</span> <span class="kn">export</span> <span class="n">AddSemigroup₃</span> <span class="o">(</span><span class="n">add_assoc₃</span><span class="o">)</span> <span class="n">whatsnew</span><span class="w"> </span><span class="k">in</span> <span class="kd">@[</span><span class="n">to_additive</span><span class="kd">]</span> <span class="kd">lemma</span><span class="w"> </span><span class="n">left_inv_eq_right_inv'</span><span class="w"> </span><span class="o">{</span><span class="n">M</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid₃</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">M</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hba</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hac</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="bp">←</span><span class="w"> </span><span class="n">one_mul</span><span class="w"> </span><span class="n">c</span><span class="o">,</span><span class="w"> </span><span class="bp">←</span><span class="w"> </span><span class="n">hba</span><span class="o">,</span><span class="w"> </span><span class="n">mul_assoc₃</span><span class="o">,</span><span class="w"> </span><span class="n">hac</span><span class="o">,</span><span class="w"> </span><span class="n">mul_one</span><span class="w"> </span><span class="n">b</span><span class="o">]</span> <span class="n">whatsnew</span> <span class="k">in</span> <span class="kd">@[to_additive]</span> <span class="kd">lemma</span> <span class="n">left_inv_eq_right_inv'</span> <span class="o">{</span><span class="n">M</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">}</span> <span class="o">[</span><span class="n">Monoid₃</span> <span class="n">M</span><span class="o">]</span> <span class="o">{</span><span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">M</span><span class="o">}</span> <span class="o">(</span><span class="n">hba</span> <span class="o">:</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">=</span> <span class="mi">1</span><span class="o">)</span> <span class="o">(</span><span class="n">hac</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">c</span> <span class="bp">=</span> <span class="mi">1</span><span class="o">)</span> <span class="o">:</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">c</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="bp">←</span> <span class="n">one_mul</span> <span class="n">c</span><span class="o">,</span> <span class="bp">←</span> <span class="n">hba</span><span class="o">,</span> <span class="n">mul_assoc₃</span><span class="o">,</span> <span class="n">hac</span><span class="o">,</span> <span class="n">mul_one</span> <span class="n">b</span><span class="o">]</span> <span class="k">#check</span><span class="w"> </span><span class="n">left_neg_eq_right_neg'</span> <span class="k">#check</span> <span class="n">left_neg_eq_right_neg'</span> </pre></div> </div> <p>Equipped with this technology, we can easily define also commutative semigroups, monoids and groups, and then define rings.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span><span class="w"> </span><span class="n">AddCommSemigroup₃</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="kd">extends</span><span class="w"> </span><span class="n">AddSemigroup₃</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">add_comm</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">a</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span> <span class="n">AddCommSemigroup₃</span> <span class="o">(</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="kd">extends</span> <span class="n">AddSemigroup₃</span> <span class="n">α</span> <span class="n">where</span> <span class="n">add_comm</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">α</span><span class="o">,</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">b</span> <span class="bp">+</span> <span class="n">a</span> <span class="kd">@[</span><span class="n">to_additive</span><span class="w"> </span><span class="n">AddCommSemigroup₃</span><span class="kd">]</span> <span class="kd">class</span><span class="w"> </span><span class="n">CommSemigroup₃</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="kd">extends</span><span class="w"> </span><span class="n">Semigroup₃</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">mul_comm</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span> <span class="kd">@[to_additive AddCommSemigroup₃]</span> <span class="kd">class</span> <span class="n">CommSemigroup₃</span> <span class="o">(</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="kd">extends</span> <span class="n">Semigroup₃</span> <span class="n">α</span> <span class="n">where</span> <span class="n">mul_comm</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">α</span><span class="o">,</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">a</span> <span class="kd">class</span><span class="w"> </span><span class="n">AddCommMonoid₃</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="kd">extends</span><span class="w"> </span><span class="n">AddMonoid₃</span><span class="w"> </span><span class="n">α</span><span class="o">,</span><span class="w"> </span><span class="n">AddCommSemigroup₃</span><span class="w"> </span><span class="n">α</span> <span class="kd">class</span> <span class="n">AddCommMonoid₃</span> <span class="o">(</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="kd">extends</span> <span class="n">AddMonoid₃</span> <span class="n">α</span><span class="o">,</span> <span class="n">AddCommSemigroup₃</span> <span class="n">α</span> <span class="kd">@[</span><span class="n">to_additive</span><span class="w"> </span><span class="n">AddCommMonoid₃</span><span class="kd">]</span> <span class="kd">class</span><span class="w"> </span><span class="n">CommMonoid₃</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="kd">extends</span><span class="w"> </span><span class="n">Monoid₃</span><span class="w"> </span><span class="n">α</span><span class="o">,</span><span class="w"> </span><span class="n">CommSemigroup₃</span><span class="w"> </span><span class="n">α</span> <span class="kd">@[to_additive AddCommMonoid₃]</span> <span class="kd">class</span> <span class="n">CommMonoid₃</span> <span class="o">(</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="kd">extends</span> <span class="n">Monoid₃</span> <span class="n">α</span><span class="o">,</span> <span class="n">CommSemigroup₃</span> <span class="n">α</span> <span class="kd">class</span><span class="w"> </span><span class="n">AddGroup₃</span><span class="w"> </span><span class="o">(</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="kd">extends</span><span class="w"> </span><span class="n">AddMonoid₃</span><span class="w"> </span><span class="n">G</span><span class="o">,</span><span class="w"> </span><span class="n">Neg</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">neg_add</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="o">,</span><span class="w"> </span><span class="bp">-</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span> <span class="kd">class</span> <span class="n">AddGroup₃</span> <span class="o">(</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="kd">extends</span> <span class="n">AddMonoid₃</span> <span class="n">G</span><span class="o">,</span> <span class="n">Neg</span> <span class="n">G</span> <span class="n">where</span> <span class="n">neg_add</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span> <span class="o">:</span> <span class="n">G</span><span class="o">,</span> <span class="bp">-</span><span class="n">a</span> <span class="bp">+</span> <span class="n">a</span> <span class="bp">=</span> <span class="mi">0</span> <span class="kd">@[</span><span class="n">to_additive</span><span class="w"> </span><span class="n">AddGroup₃</span><span class="kd">]</span> <span class="kd">class</span><span class="w"> </span><span class="n">Group₃</span><span class="w"> </span><span class="o">(</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="kd">extends</span><span class="w"> </span><span class="n">Monoid₃</span><span class="w"> </span><span class="n">G</span><span class="o">,</span><span class="w"> </span><span class="n">Inv</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">inv_mul</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="bp">⁻¹</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span> <span class="kd">@[to_additive AddGroup₃]</span> <span class="kd">class</span> <span class="n">Group₃</span> <span class="o">(</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="kd">extends</span> <span class="n">Monoid₃</span> <span class="n">G</span><span class="o">,</span> <span class="n">Inv</span> <span class="n">G</span> <span class="n">where</span> <span class="n">inv_mul</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span> <span class="o">:</span> <span class="n">G</span><span class="o">,</span> <span class="n">a</span><span class="bp">⁻¹</span> <span class="bp">*</span> <span class="n">a</span> <span class="bp">=</span> <span class="mi">1</span> </pre></div> </div> <p>We should remember to tag lemmas with <code class="docutils literal notranslate"><span class="pre">simp</span></code> when appropriate.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">attribute</span><span class="w"> </span><span class="o">[</span><span class="n">simp</span><span class="o">]</span><span class="w"> </span><span class="n">Group₃.inv_mul</span><span class="w"> </span><span class="n">AddGroup₃.neg_add</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">attribute</span> <span class="o">[</span><span class="n">simp</span><span class="o">]</span> <span class="n">Group₃.inv_mul</span> <span class="n">AddGroup₃.neg_add</span> </pre></div> </div> <p>Then we need to repeat ourselves a bit since we switch to standard notations, but at least <code class="docutils literal notranslate"><span class="pre">to_additive</span></code> does the work of translating from the multiplicative notation to the additive one.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">@[</span><span class="n">to_additive</span><span class="kd">]</span> <span class="kd">lemma</span><span class="w"> </span><span class="n">inv_eq_of_mul</span><span class="w"> </span><span class="o">[</span><span class="n">Group₃</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="bp">⁻¹</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">@[to_additive]</span> <span class="kd">lemma</span> <span class="n">inv_eq_of_mul</span> <span class="o">[</span><span class="n">Group₃</span> <span class="n">G</span><span class="o">]</span> <span class="o">{</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">G</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">b</span> <span class="bp">=</span> <span class="mi">1</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span><span class="bp">⁻¹</span> <span class="bp">=</span> <span class="n">b</span> <span class="o">:=</span> <span class="gr">sorry</span> </pre></div> </div> <p>Note that <code class="docutils literal notranslate"><span class="pre">to_additive</span></code> can be asked to tag a lemma with <code class="docutils literal notranslate"><span class="pre">simp</span></code> and propagate that attribute to the additive version as follows.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">@[</span><span class="n">to_additive</span><span class="w"> </span><span class="o">(</span><span class="n">attr</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">simp</span><span class="o">)</span><span class="kd">]</span> <span class="kd">lemma</span><span class="w"> </span><span class="n">Group₃.mul_inv</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group₃</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="o">}</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">a</span><span class="bp">⁻¹</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">@[to_additive (attr := simp)]</span> <span class="kd">lemma</span> <span class="n">Group₃.mul_inv</span> <span class="o">{</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">}</span> <span class="o">[</span><span class="n">Group₃</span> <span class="n">G</span><span class="o">]</span> <span class="o">{</span><span class="n">a</span> <span class="o">:</span> <span class="n">G</span><span class="o">}</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">a</span><span class="bp">⁻¹</span> <span class="bp">=</span> <span class="mi">1</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">@[</span><span class="n">to_additive</span><span class="kd">]</span> <span class="kd">lemma</span><span class="w"> </span><span class="n">mul_left_cancel₃</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group₃</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">@[to_additive]</span> <span class="kd">lemma</span> <span class="n">mul_left_cancel₃</span> <span class="o">{</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">}</span> <span class="o">[</span><span class="n">Group₃</span> <span class="n">G</span><span class="o">]</span> <span class="o">{</span><span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">G</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">c</span><span class="o">)</span> <span class="o">:</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">c</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">@[</span><span class="n">to_additive</span><span class="kd">]</span> <span class="kd">lemma</span><span class="w"> </span><span class="n">mul_right_cancel₃</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group₃</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">b</span><span class="bp">*</span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">c</span><span class="bp">*</span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">@[to_additive]</span> <span class="kd">lemma</span> <span class="n">mul_right_cancel₃</span> <span class="o">{</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">}</span> <span class="o">[</span><span class="n">Group₃</span> <span class="n">G</span><span class="o">]</span> <span class="o">{</span><span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">G</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">b</span><span class="bp">*</span><span class="n">a</span> <span class="bp">=</span> <span class="n">c</span><span class="bp">*</span><span class="n">a</span><span class="o">)</span> <span class="o">:</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">c</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">class</span><span class="w"> </span><span class="n">AddCommGroup₃</span><span class="w"> </span><span class="o">(</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="kd">extends</span><span class="w"> </span><span class="n">AddGroup₃</span><span class="w"> </span><span class="n">G</span><span class="o">,</span><span class="w"> </span><span class="n">AddCommMonoid₃</span><span class="w"> </span><span class="n">G</span> <span class="kd">class</span> <span class="n">AddCommGroup₃</span> <span class="o">(</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="kd">extends</span> <span class="n">AddGroup₃</span> <span class="n">G</span><span class="o">,</span> <span class="n">AddCommMonoid₃</span> <span class="n">G</span> <span class="kd">@[</span><span class="n">to_additive</span><span class="w"> </span><span class="n">AddCommGroup₃</span><span class="kd">]</span> <span class="kd">class</span><span class="w"> </span><span class="n">CommGroup₃</span><span class="w"> </span><span class="o">(</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="kd">extends</span><span class="w"> </span><span class="n">Group₃</span><span class="w"> </span><span class="n">G</span><span class="o">,</span><span class="w"> </span><span class="n">CommMonoid₃</span><span class="w"> </span><span class="n">G</span> <span class="kd">@[to_additive AddCommGroup₃]</span> <span class="kd">class</span> <span class="n">CommGroup₃</span> <span class="o">(</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="kd">extends</span> <span class="n">Group₃</span> <span class="n">G</span><span class="o">,</span> <span class="n">CommMonoid₃</span> <span class="n">G</span> </pre></div> </div> <p>We are now ready for rings. For demonstration purposes we won’t assume that addition is
-
@@ -417,56 +413,56 @@ also because Mathlib’s algebraic hierarchy goes through semirings which aropposites so that the proof below does not work for them. What we gain here, besides a nice exercise if you have never seen it, is an example of building an instance using the syntax that allows to provide a parent structure and some extra fields.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span><span class="w"> </span><span class="n">Ring₃</span><span class="w"> </span><span class="o">(</span><span class="n">R</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="kd">extends</span><span class="w"> </span><span class="n">AddGroup₃</span><span class="w"> </span><span class="n">R</span><span class="o">,</span><span class="w"> </span><span class="n">Monoid₃</span><span class="w"> </span><span class="n">R</span><span class="o">,</span><span class="w"> </span><span class="n">MulZeroClass</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="sd">/-- Multiplication is left distributive over addition -/</span> <span class="w"> </span><span class="n">left_distrib</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">c</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span> <span class="w"> </span><span class="sd">/-- Multiplication is right distributive over addition -/</span> <span class="w"> </span><span class="n">right_distrib</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">,</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span> <span class="n">Ring₃</span> <span class="o">(</span><span class="n">R</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="kd">extends</span> <span class="n">AddGroup₃</span> <span class="n">R</span><span class="o">,</span> <span class="n">Monoid₃</span> <span class="n">R</span><span class="o">,</span> <span class="n">MulZeroClass</span> <span class="n">R</span> <span class="n">where</span> <span class="sd">/-- Multiplication is left distributive over addition -/</span> <span class="n">left_distrib</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">R</span><span class="o">,</span> <span class="n">a</span> <span class="bp">*</span> <span class="o">(</span><span class="n">b</span> <span class="bp">+</span> <span class="n">c</span><span class="o">)</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">b</span> <span class="bp">+</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">c</span> <span class="sd">/-- Multiplication is right distributive over addition -/</span> <span class="n">right_distrib</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">R</span><span class="o">,</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="bp">*</span> <span class="n">c</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">c</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">*</span> <span class="n">c</span> <span class="kd">instance</span><span class="w"> </span><span class="o">{</span><span class="n">R</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Ring₃</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">AddCommGroup₃</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="o">:=</span> <span class="o">{</span><span class="w"> </span><span class="n">Ring₃.toAddGroup₃</span><span class="w"> </span><span class="k">with</span> <span class="w"> </span><span class="n">add_comm</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span><span class="w"> </span><span class="o">}</span> <span class="kd">instance</span> <span class="o">{</span><span class="n">R</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">}</span> <span class="o">[</span><span class="n">Ring₃</span> <span class="n">R</span><span class="o">]</span> <span class="o">:</span> <span class="n">AddCommGroup₃</span> <span class="n">R</span> <span class="o">:=</span> <span class="o">{</span> <span class="n">Ring₃.toAddGroup₃</span> <span class="k">with</span> <span class="n">add_comm</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="o">}</span> </pre></div> </div> <p>Of course we can also build concrete instances, such as a ring structure on integers (of course the instance below uses that all the work is already done in Mathlib).</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Ring₃</span><span class="w"> </span><span class="n">ℤ</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">add</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">(</span><span class="bp">·</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="bp">·</span><span class="o">)</span> <span class="w"> </span><span class="n">add_assoc₃</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">add_assoc</span> <span class="w"> </span><span class="n">zero</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="mi">0</span> <span class="w"> </span><span class="n">zero_add</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">simp</span> <span class="w"> </span><span class="n">add_zero</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">simp</span> <span class="w"> </span><span class="n">neg</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">(</span><span class="bp">-</span><span class="w"> </span><span class="bp">·</span><span class="o">)</span> <span class="w"> </span><span class="n">neg_add</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">simp</span> <span class="w"> </span><span class="n">mul</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">(</span><span class="bp">·</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="bp">·</span><span class="o">)</span> <span class="w"> </span><span class="n">mul_assoc₃</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">mul_assoc</span> <span class="w"> </span><span class="n">one</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="mi">1</span> <span class="w"> </span><span class="n">one_mul</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">simp</span> <span class="w"> </span><span class="n">mul_one</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">simp</span> <span class="w"> </span><span class="n">zero_mul</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">simp</span> <span class="w"> </span><span class="n">mul_zero</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">simp</span> <span class="w"> </span><span class="n">left_distrib</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Int.mul_add</span> <span class="w"> </span><span class="n">right_distrib</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Int.add_mul</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span> <span class="o">:</span> <span class="n">Ring₃</span> <span class="n">ℤ</span> <span class="n">where</span> <span class="n">add</span> <span class="o">:=</span> <span class="o">(</span><span class="bp">·</span> <span class="bp">+</span> <span class="bp">·</span><span class="o">)</span> <span class="n">add_assoc₃</span> <span class="o">:=</span> <span class="n">add_assoc</span> <span class="n">zero</span> <span class="o">:=</span> <span class="mi">0</span> <span class="n">zero_add</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> <span class="n">add_zero</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> <span class="n">neg</span> <span class="o">:=</span> <span class="o">(</span><span class="bp">-</span> <span class="bp">·</span><span class="o">)</span> <span class="n">neg_add</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> <span class="n">mul</span> <span class="o">:=</span> <span class="o">(</span><span class="bp">·</span> <span class="bp">*</span> <span class="bp">·</span><span class="o">)</span> <span class="n">mul_assoc₃</span> <span class="o">:=</span> <span class="n">mul_assoc</span> <span class="n">one</span> <span class="o">:=</span> <span class="mi">1</span> <span class="n">one_mul</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> <span class="n">mul_one</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> <span class="n">zero_mul</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> <span class="n">mul_zero</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> <span class="n">left_distrib</span> <span class="o">:=</span> <span class="n">Int.mul_add</span> <span class="n">right_distrib</span> <span class="o">:=</span> <span class="n">Int.add_mul</span> </pre></div> </div> <p>As an exercise you can now set up a simple hierarchy for order relations, including a class for ordered commutative monoids, which have both a partial order and a commutative monoid structure such that <code class="docutils literal notranslate"><span class="pre">∀</span> <span class="pre">a</span> <span class="pre">b</span> <span class="pre">:</span> <span class="pre">α,</span> <span class="pre">a</span> <span class="pre">≤</span> <span class="pre">b</span> <span class="pre">→</span> <span class="pre">∀</span> <span class="pre">c</span> <span class="pre">:</span> <span class="pre">α,</span> <span class="pre">c</span> <span class="pre">*</span> <span class="pre">a</span> <span class="pre">≤</span> <span class="pre">c</span> <span class="pre">*</span> <span class="pre">b</span></code>. Of course you need to add fields and maybe <code class="docutils literal notranslate"><span class="pre">extends</span></code> clauses to the following classes.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span><span class="w"> </span><span class="n">LE₁</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="sd">/-- The Less-or-Equal relation. -/</span> <span class="w"> </span><span class="n">le</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="kt">Prop</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span> <span class="n">LE₁</span> <span class="o">(</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="n">where</span> <span class="sd">/-- The Less-or-Equal relation. -/</span> <span class="n">le</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">α</span> <span class="bp">→</span> <span class="kt">Prop</span> <span class="kd">@[</span><span class="n">inherit_doc</span><span class="kd">]</span><span class="w"> </span><span class="kd">infix</span><span class="o">:</span><span class="mi">50</span><span class="w"> </span><span class="s2">" ≤₁ "</span><span class="w"> </span><span class="bp">=></span><span class="w"> </span><span class="n">LE₁.le</span> <span class="kd">@[inherit_doc]</span> <span class="kd">infix</span><span class="o">:</span><span class="mi">50</span> <span class="s2">" ≤₁ "</span> <span class="bp">=></span> <span class="n">LE₁.le</span> <span class="kd">class</span><span class="w"> </span><span class="n">Preorder₁</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span> <span class="kd">class</span> <span class="n">Preorder₁</span> <span class="o">(</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="kd">class</span><span class="w"> </span><span class="n">PartialOrder₁</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span> <span class="kd">class</span> <span class="n">PartialOrder₁</span> <span class="o">(</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="kd">class</span><span class="w"> </span><span class="n">OrderedCommMonoid₁</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span> <span class="kd">class</span> <span class="n">OrderedCommMonoid₁</span> <span class="o">(</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="kd">instance</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">OrderedCommMonoid₁</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="n">where</span> <span class="kd">instance</span> <span class="o">:</span> <span class="n">OrderedCommMonoid₁</span> <span class="n">ℕ</span> <span class="n">where</span> </pre></div> </div> <p>We now want to discuss algebraic structures involving several types. The prime example
-
@@ -475,20 +471,20 @@ and think that all our rings are fields. Those structures are commutative additiequipped with a scalar multiplication by elements of some ring.</p> <p>We first define the data-carrying type class of scalar multiplication by some type <code class="docutils literal notranslate"><span class="pre">α</span></code> on some type <code class="docutils literal notranslate"><span class="pre">β</span></code>, and give it a right associative notation.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span><span class="w"> </span><span class="n">SMul₃</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">β</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="sd">/-- Scalar multiplication -/</span> <span class="w"> </span><span class="n">smul</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">β</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">β</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span> <span class="n">SMul₃</span> <span class="o">(</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="o">(</span><span class="n">β</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="n">where</span> <span class="sd">/-- Scalar multiplication -/</span> <span class="n">smul</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">β</span> <span class="bp">→</span> <span class="n">β</span> <span class="kd">infixr</span><span class="o">:</span><span class="mi">73</span><span class="w"> </span><span class="s2">" • "</span><span class="w"> </span><span class="bp">=></span><span class="w"> </span><span class="n">SMul₃.smul</span> <span class="kd">infixr</span><span class="o">:</span><span class="mi">73</span> <span class="s2">" • "</span> <span class="bp">=></span> <span class="n">SMul₃.smul</span> </pre></div> </div> <p>Then we can define modules (again think about vector spaces if you don’t know what is a module).</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span><span class="w"> </span><span class="n">Module₁</span><span class="w"> </span><span class="o">(</span><span class="n">R</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">Ring₃</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">M</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">AddCommGroup₃</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="kd">extends</span><span class="w"> </span><span class="n">SMul₃</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">zero_smul</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">M</span><span class="o">,</span><span class="w"> </span><span class="o">(</span><span class="mi">0</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span> <span class="w"> </span><span class="n">one_smul</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">M</span><span class="o">,</span><span class="w"> </span><span class="o">(</span><span class="mi">1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">m</span> <span class="w"> </span><span class="n">mul_smul</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">m</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">M</span><span class="o">),</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">m</span> <span class="w"> </span><span class="n">add_smul</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">m</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">M</span><span class="o">),</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">m</span> <span class="w"> </span><span class="n">smul_add</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">m</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">M</span><span class="o">),</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="o">(</span><span class="n">m</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">n</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span> <span class="n">Module₁</span> <span class="o">(</span><span class="n">R</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="o">[</span><span class="n">Ring₃</span> <span class="n">R</span><span class="o">]</span> <span class="o">(</span><span class="n">M</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="o">[</span><span class="n">AddCommGroup₃</span> <span class="n">M</span><span class="o">]</span> <span class="kd">extends</span> <span class="n">SMul₃</span> <span class="n">R</span> <span class="n">M</span> <span class="n">where</span> <span class="n">zero_smul</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">m</span> <span class="o">:</span> <span class="n">M</span><span class="o">,</span> <span class="o">(</span><span class="mi">0</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="bp">•</span> <span class="n">m</span> <span class="bp">=</span> <span class="mi">0</span> <span class="n">one_smul</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">m</span> <span class="o">:</span> <span class="n">M</span><span class="o">,</span> <span class="o">(</span><span class="mi">1</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="bp">•</span> <span class="n">m</span> <span class="bp">=</span> <span class="n">m</span> <span class="n">mul_smul</span> <span class="o">:</span> <span class="bp">∀</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="o">(</span><span class="n">m</span> <span class="o">:</span> <span class="n">M</span><span class="o">),</span> <span class="o">(</span><span class="n">a</span> <span class="bp">*</span> <span class="n">b</span><span class="o">)</span> <span class="bp">•</span> <span class="n">m</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">•</span> <span class="n">b</span> <span class="bp">•</span> <span class="n">m</span> <span class="n">add_smul</span> <span class="o">:</span> <span class="bp">∀</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="o">(</span><span class="n">m</span> <span class="o">:</span> <span class="n">M</span><span class="o">),</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="bp">•</span> <span class="n">m</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">•</span> <span class="n">m</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">•</span> <span class="n">m</span> <span class="n">smul_add</span> <span class="o">:</span> <span class="bp">∀</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="o">(</span><span class="n">m</span> <span class="n">n</span> <span class="o">:</span> <span class="n">M</span><span class="o">),</span> <span class="n">a</span> <span class="bp">•</span> <span class="o">(</span><span class="n">m</span> <span class="bp">+</span> <span class="n">n</span><span class="o">)</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">•</span> <span class="n">m</span> <span class="bp">+</span> <span class="n">a</span> <span class="bp">•</span> <span class="n">n</span> </pre></div> </div> <p>There is something interesting going on here. While it isn’t too surprising that the
-
@@ -515,13 +511,13 @@ safely be used as an instance. The rule is easy to remember: each class appearin<code class="docutils literal notranslate"><span class="pre">extends</span></code> clause should mention every type appearing in the parameters.</p> <p>Let us create our first module instance: a ring is a module over itself using its multiplication as a scalar multiplication.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span><span class="w"> </span><span class="n">selfModule</span><span class="w"> </span><span class="o">(</span><span class="n">R</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">Ring₃</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Module₁</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">smul</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">r</span><span class="bp">*</span><span class="n">s</span> <span class="w"> </span><span class="n">zero_smul</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">zero_mul</span> <span class="w"> </span><span class="n">one_smul</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">one_mul</span> <span class="w"> </span><span class="n">mul_smul</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">mul_assoc₃</span> <span class="w"> </span><span class="n">add_smul</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Ring₃.right_distrib</span> <span class="w"> </span><span class="n">smul_add</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Ring₃.left_distrib</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span> <span class="n">selfModule</span> <span class="o">(</span><span class="n">R</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="o">[</span><span class="n">Ring₃</span> <span class="n">R</span><span class="o">]</span> <span class="o">:</span> <span class="n">Module₁</span> <span class="n">R</span> <span class="n">R</span> <span class="n">where</span> <span class="n">smul</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">r</span> <span class="n">s</span> <span class="bp">↦</span> <span class="n">r</span><span class="bp">*</span><span class="n">s</span> <span class="n">zero_smul</span> <span class="o">:=</span> <span class="n">zero_mul</span> <span class="n">one_smul</span> <span class="o">:=</span> <span class="n">one_mul</span> <span class="n">mul_smul</span> <span class="o">:=</span> <span class="n">mul_assoc₃</span> <span class="n">add_smul</span> <span class="o">:=</span> <span class="n">Ring₃.right_distrib</span> <span class="n">smul_add</span> <span class="o">:=</span> <span class="n">Ring₃.left_distrib</span> </pre></div> </div> <p>As a second example, every abelian group is a module over <code class="docutils literal notranslate"><span class="pre">ℤ</span></code> (this is one of the reason to
-
@@ -529,26 +525,26 @@ generalize the theory of vector spaces by allowing non-invertible scalars). Firsscalar multiplication by a natural number for any type equipped with a zero and an addition: <code class="docutils literal notranslate"><span class="pre">n</span> <span class="pre">•</span> <span class="pre">a</span></code> is defined as <code class="docutils literal notranslate"><span class="pre">a</span> <span class="pre">+</span> <span class="pre">⋯</span> <span class="pre">+</span> <span class="pre">a</span></code> where <code class="docutils literal notranslate"><span class="pre">a</span></code> appears <code class="docutils literal notranslate"><span class="pre">n</span></code> times. Then this is extended to scalar multiplication by an integer by ensuring <code class="docutils literal notranslate"><span class="pre">(-1)</span> <span class="pre">•</span> <span class="pre">a</span> <span class="pre">=</span> <span class="pre">-a</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">nsmul₁</span><span class="w"> </span><span class="o">[</span><span class="n">Zero</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Add</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">M</span> <span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="mi">0</span><span class="o">,</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">=></span><span class="w"> </span><span class="mi">0</span> <span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=></span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">nsmul₁</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">a</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">nsmul₁</span> <span class="o">[</span><span class="n">Zero</span> <span class="n">M</span><span class="o">]</span> <span class="o">[</span><span class="n">Add</span> <span class="n">M</span><span class="o">]</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">M</span> <span class="bp">→</span> <span class="n">M</span> <span class="bp">|</span> <span class="mi">0</span><span class="o">,</span> <span class="n">_</span> <span class="bp">=></span> <span class="mi">0</span> <span class="bp">|</span> <span class="n">n</span> <span class="bp">+</span> <span class="mi">1</span><span class="o">,</span> <span class="n">a</span> <span class="bp">=></span> <span class="n">a</span> <span class="bp">+</span> <span class="n">nsmul₁</span> <span class="n">n</span> <span class="n">a</span> <span class="kd">def</span><span class="w"> </span><span class="n">zsmul₁</span><span class="w"> </span><span class="o">{</span><span class="n">M</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Zero</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Add</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Neg</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℤ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">M</span> <span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">Int.ofNat</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=></span><span class="w"> </span><span class="n">nsmul₁</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">a</span> <span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">Int.negSucc</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=></span><span class="w"> </span><span class="bp">-</span><span class="n">nsmul₁</span><span class="w"> </span><span class="n">n.succ</span><span class="w"> </span><span class="n">a</span> <span class="kd">def</span> <span class="n">zsmul₁</span> <span class="o">{</span><span class="n">M</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Zero</span> <span class="n">M</span><span class="o">]</span> <span class="o">[</span><span class="n">Add</span> <span class="n">M</span><span class="o">]</span> <span class="o">[</span><span class="n">Neg</span> <span class="n">M</span><span class="o">]</span> <span class="o">:</span> <span class="n">ℤ</span> <span class="bp">→</span> <span class="n">M</span> <span class="bp">→</span> <span class="n">M</span> <span class="bp">|</span> <span class="n">Int.ofNat</span> <span class="n">n</span><span class="o">,</span> <span class="n">a</span> <span class="bp">=></span> <span class="n">nsmul₁</span> <span class="n">n</span> <span class="n">a</span> <span class="bp">|</span> <span class="n">Int.negSucc</span> <span class="n">n</span><span class="o">,</span> <span class="n">a</span> <span class="bp">=></span> <span class="bp">-</span><span class="n">nsmul₁</span> <span class="n">n.succ</span> <span class="n">a</span> </pre></div> </div> <p>Proving this gives rise to a module structure is a bit tedious and not interesting for the current discussion, so we will sorry all axioms. You are <em>not</em> asked to replace those sorries with proofs. If you insist on doing it then you will probably want to state and prove several intermediate lemmas about <code class="docutils literal notranslate"><span class="pre">nsmul₁</span></code> and <code class="docutils literal notranslate"><span class="pre">zsmul₁</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span><span class="w"> </span><span class="n">abGrpModule</span><span class="w"> </span><span class="o">(</span><span class="n">A</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">AddCommGroup₃</span><span class="w"> </span><span class="n">A</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Module₁</span><span class="w"> </span><span class="n">ℤ</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">smul</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">zsmul₁</span> <span class="w"> </span><span class="n">zero_smul</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">one_smul</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">mul_smul</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">add_smul</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">smul_add</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span> <span class="n">abGrpModule</span> <span class="o">(</span><span class="n">A</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="o">[</span><span class="n">AddCommGroup₃</span> <span class="n">A</span><span class="o">]</span> <span class="o">:</span> <span class="n">Module₁</span> <span class="n">ℤ</span> <span class="n">A</span> <span class="n">where</span> <span class="n">smul</span> <span class="o">:=</span> <span class="n">zsmul₁</span> <span class="n">zero_smul</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="n">one_smul</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="n">mul_smul</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="n">add_smul</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="n">smul_add</span> <span class="o">:=</span> <span class="gr">sorry</span> </pre></div> </div> <p>A much more important issue is that we now have two module structures over the ring <code class="docutils literal notranslate"><span class="pre">ℤ</span></code>
-
@@ -559,10 +555,10 @@ this isn’t true by definition, it requires a proof. This is very bad newsinstance resolution procedure and will lead to very frustrating failures for users of this hierarchy. When directly asked to find an instance, Lean will pick one, and we can see which one using:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="bp">#</span><span class="n">synth</span><span class="w"> </span><span class="n">Module₁</span><span class="w"> </span><span class="n">ℤ</span><span class="w"> </span><span class="n">ℤ</span><span class="w"> </span><span class="c1">-- abGrpModule ℤ</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="bp">#</span><span class="n">synth</span> <span class="n">Module₁</span> <span class="n">ℤ</span> <span class="n">ℤ</span> <span class="c1">-- abGrpModule ℤ</span> </pre></div> </div> <p>But in a more indirect context it can happen that Lean infers the one and then gets confused. <p>But in a more indirect context it can happen that Lean infers the other one and then gets confused. This situation is known as a bad diamond. This has nothing to do with the diamond operation we used above, it refers to the way one can draw the paths from <code class="docutils literal notranslate"><span class="pre">ℤ</span></code> to its <code class="docutils literal notranslate"><span class="pre">Module₁</span> <span class="pre">ℤ</span></code> going through either <code class="docutils literal notranslate"><span class="pre">AddCommGroup₃</span> <span class="pre">ℤ</span></code> or <code class="docutils literal notranslate"><span class="pre">Ring₃</span> <span class="pre">ℤ</span></code>.</p>
-
@@ -576,53 +572,53 @@ cannot be bad since any too proofs of the same statement are definitionally equafield which is data, not a proof, and we have two constructions that are not definitionally equal. The robust way of fixing this issue is to make sure that going from a rich structure to a poor structure is always done by forgetting data, not by defining data. This well-known pattern as been named “forgetful inheritance” and extensively discussed in <a class="reference external" href="https://inria.hal.science/hal-02463336">https://inria.hal.science/hal-02463336</a>.</p> has been named “forgetful inheritance” and extensively discussed in <a class="reference external" href="https://inria.hal.science/hal-02463336v2">https://inria.hal.science/hal-02463336v2</a>.</p> <p>In our concrete case, we can modify the definition of <code class="docutils literal notranslate"><span class="pre">AddMonoid₃</span></code> to include a <code class="docutils literal notranslate"><span class="pre">nsmul</span></code> data field and some <code class="docutils literal notranslate"><span class="pre">Prop</span></code>-valued fields ensuring this operation is provably the one we constructed above. Those fields are given default values using <code class="docutils literal notranslate"><span class="pre">:=</span></code> after their type in the definition below. Thanks to these default values, most instances would be constructed exactly as with our previous definitions. But in the special case of <code class="docutils literal notranslate"><span class="pre">ℤ</span></code> we will be able to provide specific values.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span><span class="w"> </span><span class="n">AddMonoid₄</span><span class="w"> </span><span class="o">(</span><span class="n">M</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="kd">extends</span><span class="w"> </span><span class="n">AddSemigroup₃</span><span class="w"> </span><span class="n">M</span><span class="o">,</span><span class="w"> </span><span class="n">AddZeroClass</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="sd">/-- Multiplication by a natural number. -/</span> <span class="w"> </span><span class="n">nsmul</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">nsmul₁</span> <span class="w"> </span><span class="sd">/-- Multiplication by `(0 : ℕ)` gives `0`. -/</span> <span class="w"> </span><span class="n">nsmul_zero</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">nsmul</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">intros</span><span class="bp">;</span><span class="w"> </span><span class="n">rfl</span> <span class="w"> </span><span class="sd">/-- Multiplication by `(n + 1 : ℕ)` behaves as expected. -/</span> <span class="w"> </span><span class="n">nsmul_succ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="o">),</span><span class="w"> </span><span class="n">nsmul</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">nsmul</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">intros</span><span class="bp">;</span><span class="w"> </span><span class="n">rfl</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span> <span class="n">AddMonoid₄</span> <span class="o">(</span><span class="n">M</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="kd">extends</span> <span class="n">AddSemigroup₃</span> <span class="n">M</span><span class="o">,</span> <span class="n">AddZeroClass</span> <span class="n">M</span> <span class="n">where</span> <span class="sd">/-- Multiplication by a natural number. -/</span> <span class="n">nsmul</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">M</span> <span class="bp">→</span> <span class="n">M</span> <span class="o">:=</span> <span class="n">nsmul₁</span> <span class="sd">/-- Multiplication by `(0 : ℕ)` gives `0`. -/</span> <span class="n">nsmul_zero</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span><span class="o">,</span> <span class="n">nsmul</span> <span class="mi">0</span> <span class="n">x</span> <span class="bp">=</span> <span class="mi">0</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intros</span><span class="bp">;</span> <span class="n">rfl</span> <span class="sd">/-- Multiplication by `(n + 1 : ℕ)` behaves as expected. -/</span> <span class="n">nsmul_succ</span> <span class="o">:</span> <span class="bp">∀</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">(</span><span class="n">x</span><span class="o">),</span> <span class="n">nsmul</span> <span class="o">(</span><span class="n">n</span> <span class="bp">+</span> <span class="mi">1</span><span class="o">)</span> <span class="n">x</span> <span class="bp">=</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">nsmul</span> <span class="n">n</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intros</span><span class="bp">;</span> <span class="n">rfl</span> <span class="kd">instance</span><span class="w"> </span><span class="n">mySMul</span><span class="w"> </span><span class="o">{</span><span class="n">M</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">AddMonoid₄</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">SMul</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">⟨</span><span class="n">AddMonoid₄.nsmul</span><span class="o">⟩</span> <span class="kd">instance</span> <span class="n">mySMul</span> <span class="o">{</span><span class="n">M</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">}</span> <span class="o">[</span><span class="n">AddMonoid₄</span> <span class="n">M</span><span class="o">]</span> <span class="o">:</span> <span class="n">SMul</span> <span class="n">ℕ</span> <span class="n">M</span> <span class="o">:=</span> <span class="o">⟨</span><span class="n">AddMonoid₄.nsmul</span><span class="o">⟩</span> </pre></div> </div> <p>Let us check we can still construct a product monoid instance without providing the <code class="docutils literal notranslate"><span class="pre">nsmul</span></code> related fields.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span><span class="w"> </span><span class="o">(</span><span class="n">M</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">AddMonoid₄</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">AddMonoid₄</span><span class="w"> </span><span class="n">N</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">AddMonoid₄</span><span class="w"> </span><span class="o">(</span><span class="n">M</span><span class="w"> </span><span class="bp">×</span><span class="w"> </span><span class="n">N</span><span class="o">)</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">add</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="n">q</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="o">(</span><span class="n">p</span><span class="bp">.</span><span class="mi">1</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">q</span><span class="bp">.</span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="n">p</span><span class="bp">.</span><span class="mi">2</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">q</span><span class="bp">.</span><span class="mi">2</span><span class="o">)</span> <span class="w"> </span><span class="n">add_assoc₃</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">ext</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">add_assoc₃</span> <span class="w"> </span><span class="n">zero</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">(</span><span class="mi">0</span><span class="o">,</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span> <span class="w"> </span><span class="n">zero_add</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">ext</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">zero_add</span> <span class="w"> </span><span class="n">add_zero</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">ext</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">add_zero</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span> <span class="o">(</span><span class="n">M</span> <span class="n">N</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="o">[</span><span class="n">AddMonoid₄</span> <span class="n">M</span><span class="o">]</span> <span class="o">[</span><span class="n">AddMonoid₄</span> <span class="n">N</span><span class="o">]</span> <span class="o">:</span> <span class="n">AddMonoid₄</span> <span class="o">(</span><span class="n">M</span> <span class="bp">×</span> <span class="n">N</span><span class="o">)</span> <span class="n">where</span> <span class="n">add</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">p</span> <span class="n">q</span> <span class="bp">↦</span> <span class="o">(</span><span class="n">p.1</span> <span class="bp">+</span> <span class="n">q.1</span><span class="o">,</span> <span class="n">p.2</span> <span class="bp">+</span> <span class="n">q.2</span><span class="o">)</span> <span class="n">add_assoc₃</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="bp">↦</span> <span class="kd">by</span> <span class="n">ext</span> <span class="bp"><;></span> <span class="n">apply</span> <span class="n">add_assoc₃</span> <span class="n">zero</span> <span class="o">:=</span> <span class="o">(</span><span class="mi">0</span><span class="o">,</span> <span class="mi">0</span><span class="o">)</span> <span class="n">zero_add</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">a</span> <span class="bp">↦</span> <span class="kd">by</span> <span class="n">ext</span> <span class="bp"><;></span> <span class="n">apply</span> <span class="n">zero_add</span> <span class="n">add_zero</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">a</span> <span class="bp">↦</span> <span class="kd">by</span> <span class="n">ext</span> <span class="bp"><;></span> <span class="n">apply</span> <span class="n">add_zero</span> </pre></div> </div> <p>And now let us handle the special case of <code class="docutils literal notranslate"><span class="pre">ℤ</span></code> where we want to build <code class="docutils literal notranslate"><span class="pre">nsmul</span></code> using the coercion of <code class="docutils literal notranslate"><span class="pre">ℕ</span></code> to <code class="docutils literal notranslate"><span class="pre">ℤ</span></code> and the multiplication on <code class="docutils literal notranslate"><span class="pre">ℤ</span></code>. Note in particular how the proof fields contain more work than in the default value above.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">AddMonoid₄</span><span class="w"> </span><span class="n">ℤ</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">add</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">(</span><span class="bp">·</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="bp">·</span><span class="o">)</span> <span class="w"> </span><span class="n">add_assoc₃</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Int.add_assoc</span> <span class="w"> </span><span class="n">zero</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="mi">0</span> <span class="w"> </span><span class="n">zero_add</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Int.zero_add</span> <span class="w"> </span><span class="n">add_zero</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Int.add_zero</span> <span class="w"> </span><span class="n">nsmul</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℤ</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">m</span> <span class="w"> </span><span class="n">nsmul_zero</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Int.zero_mul</span> <span class="w"> </span><span class="n">nsmul_succ</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="k">show</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℤ</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">m</span> <span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">Int.add_mul</span><span class="o">,</span><span class="w"> </span><span class="n">Int.add_comm</span><span class="o">,</span><span class="w"> </span><span class="n">Int.one_mul</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span> <span class="o">:</span> <span class="n">AddMonoid₄</span> <span class="n">ℤ</span> <span class="n">where</span> <span class="n">add</span> <span class="o">:=</span> <span class="o">(</span><span class="bp">·</span> <span class="bp">+</span> <span class="bp">·</span><span class="o">)</span> <span class="n">add_assoc₃</span> <span class="o">:=</span> <span class="n">Int.add_assoc</span> <span class="n">zero</span> <span class="o">:=</span> <span class="mi">0</span> <span class="n">zero_add</span> <span class="o">:=</span> <span class="n">Int.zero_add</span> <span class="n">add_zero</span> <span class="o">:=</span> <span class="n">Int.add_zero</span> <span class="n">nsmul</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">n</span> <span class="n">m</span> <span class="bp">↦</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">ℤ</span><span class="o">)</span> <span class="bp">*</span> <span class="n">m</span> <span class="n">nsmul_zero</span> <span class="o">:=</span> <span class="n">Int.zero_mul</span> <span class="n">nsmul_succ</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">n</span> <span class="n">m</span> <span class="bp">↦</span> <span class="k">show</span> <span class="o">(</span><span class="n">n</span> <span class="bp">+</span> <span class="mi">1</span> <span class="o">:</span> <span class="n">ℤ</span><span class="o">)</span> <span class="bp">*</span> <span class="n">m</span> <span class="bp">=</span> <span class="n">m</span> <span class="bp">+</span> <span class="n">n</span> <span class="bp">*</span> <span class="n">m</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">Int.add_mul</span><span class="o">,</span> <span class="n">Int.add_comm</span><span class="o">,</span> <span class="n">Int.one_mul</span><span class="o">]</span> </pre></div> </div> <p>Let us check we solved our issue. Because Lean already has a definition of scalar multiplication of a natural number and an integer, and we want to make sure our instance is used, we won’t use the <code class="docutils literal notranslate"><span class="pre">•</span></code> notation but call <code class="docutils literal notranslate"><span class="pre">SMul.mul</span></code> and explicitly provide our instance defined above.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">m</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℤ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">SMul.smul</span><span class="w"> </span><span class="o">(</span><span class="n">self</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">mySMul</span><span class="o">)</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">rfl</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">(</span><span class="n">m</span> <span class="o">:</span> <span class="n">ℤ</span><span class="o">)</span> <span class="o">:</span> <span class="n">SMul.smul</span> <span class="o">(</span><span class="n">self</span> <span class="o">:=</span> <span class="n">mySMul</span><span class="o">)</span> <span class="n">n</span> <span class="n">m</span> <span class="bp">=</span> <span class="n">n</span> <span class="bp">*</span> <span class="n">m</span> <span class="o">:=</span> <span class="n">rfl</span> </pre></div> </div> <p>This story then continues with incorporating a <code class="docutils literal notranslate"><span class="pre">zsmul</span></code> field into the definition of groups
-
@@ -636,20 +632,20 @@ that every preorder comes with a <code class="docutils literal notranslate"><spa-/</p> </section> <section id="morphisms"> <span id="section-hierarchies-morphisms"></span><h2><span class="section-number">7.2. </span>Morphisms<a class="headerlink" href="#morphisms" title="Link to this heading"></a></h2> <span id="section-hierarchies-morphisms"></span><h2><span class="section-number">7.2. </span>Morphisms<a class="headerlink" href="#morphisms" title="Permalink to this heading"></a></h2> <p>So far in this chapter, we discussed how to create a hierarchy of mathematical structures. But defining structures is not really completed until we have morphisms. There are two main approaches here. The most obvious one is to define a predicate on functions.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">isMonoidHom₁</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">H</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">H</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Prop</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">g'</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">g</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">g'</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g'</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">isMonoidHom₁</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">G</span><span class="o">]</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">H</span><span class="o">]</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">→</span> <span class="n">H</span><span class="o">)</span> <span class="o">:</span> <span class="kt">Prop</span> <span class="o">:=</span> <span class="n">f</span> <span class="mi">1</span> <span class="bp">=</span> <span class="mi">1</span> <span class="bp">∧</span> <span class="bp">∀</span> <span class="n">g</span> <span class="n">g'</span><span class="o">,</span> <span class="n">f</span> <span class="o">(</span><span class="n">g</span> <span class="bp">*</span> <span class="n">g'</span><span class="o">)</span> <span class="bp">=</span> <span class="n">f</span> <span class="n">g</span> <span class="bp">*</span> <span class="n">f</span> <span class="n">g'</span> </pre></div> </div> <p>In this definition, it is a bit unpleasant to use a conjunction. In particular users will need to remember the ordering we chose when they want to access the two conditions. So we could use a structure instead.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">structure</span><span class="w"> </span><span class="n">isMonoidHom₂</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">H</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">H</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Prop</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">map_one</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span> <span class="w"> </span><span class="n">map_mul</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">g'</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">g</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">g'</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g'</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">structure</span> <span class="n">isMonoidHom₂</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">G</span><span class="o">]</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">H</span><span class="o">]</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">→</span> <span class="n">H</span><span class="o">)</span> <span class="o">:</span> <span class="kt">Prop</span> <span class="n">where</span> <span class="n">map_one</span> <span class="o">:</span> <span class="n">f</span> <span class="mi">1</span> <span class="bp">=</span> <span class="mi">1</span> <span class="n">map_mul</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">g</span> <span class="n">g'</span><span class="o">,</span> <span class="n">f</span> <span class="o">(</span><span class="n">g</span> <span class="bp">*</span> <span class="n">g'</span><span class="o">)</span> <span class="bp">=</span> <span class="n">f</span> <span class="n">g</span> <span class="bp">*</span> <span class="n">f</span> <span class="n">g'</span> </pre></div> </div> <p>Once we are here, it is even tempting to make it a class and use the type class instance resolution
-
@@ -667,17 +663,17 @@ It really feels like “monoid morphism” is not an adjective you can ait is a noun. On the other hand one can argue that a continuous function between topological spaces is really a function that happens to be continuous. This is one reason why Mathlib has a <code class="docutils literal notranslate"><span class="pre">Continuous</span></code> predicate. For instance you can write:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Continuous</span><span class="w"> </span><span class="o">(</span><span class="n">id</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">continuous_id</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">Continuous</span> <span class="o">(</span><span class="n">id</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:=</span> <span class="n">continuous_id</span> </pre></div> </div> <p>We still have bundles continuous functions, which are convenient for instance to put a topology on a space of continuous functions, but they are not the primary tool to work with continuity.</p> <p>By contrast, morphisms between monoids (or other algebraic structures) are bundled as in:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">@[</span><span class="n">ext</span><span class="kd">]</span> <span class="kd">structure</span><span class="w"> </span><span class="n">MonoidHom₁</span><span class="w"> </span><span class="o">(</span><span class="n">G</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">H</span><span class="o">]</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">toFun</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">H</span> <span class="w"> </span><span class="n">map_one</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">toFun</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span> <span class="w"> </span><span class="n">map_mul</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">g'</span><span class="o">,</span><span class="w"> </span><span class="n">toFun</span><span class="w"> </span><span class="o">(</span><span class="n">g</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">g'</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">toFun</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">toFun</span><span class="w"> </span><span class="n">g'</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">@[ext]</span> <span class="kd">structure</span> <span class="n">MonoidHom₁</span> <span class="o">(</span><span class="n">G</span> <span class="n">H</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">G</span><span class="o">]</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">H</span><span class="o">]</span> <span class="n">where</span> <span class="n">toFun</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">→</span> <span class="n">H</span> <span class="n">map_one</span> <span class="o">:</span> <span class="n">toFun</span> <span class="mi">1</span> <span class="bp">=</span> <span class="mi">1</span> <span class="n">map_mul</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">g</span> <span class="n">g'</span><span class="o">,</span> <span class="n">toFun</span> <span class="o">(</span><span class="n">g</span> <span class="bp">*</span> <span class="n">g'</span><span class="o">)</span> <span class="bp">=</span> <span class="n">toFun</span> <span class="n">g</span> <span class="bp">*</span> <span class="n">toFun</span> <span class="n">g'</span> </pre></div> </div> <p>Of course we don’t want to type <code class="docutils literal notranslate"><span class="pre">toFun</span></code> everywhere so we register a coercion using
-
@@ -685,30 +681,30 @@ the <code class="docutils literal notranslate"><span class="pre">CoeFun</span></The second argument describes the target function type. In our case it is always <code class="docutils literal notranslate"><span class="pre">G</span> <span class="pre">→</span> <span class="pre">H</span></code> for every <code class="docutils literal notranslate"><span class="pre">f</span> <span class="pre">:</span> <span class="pre">MonoidHom₁</span> <span class="pre">G</span> <span class="pre">H</span></code>. We also tag <code class="docutils literal notranslate"><span class="pre">MonoidHom₁.toFun</span></code> with the <code class="docutils literal notranslate"><span class="pre">coe</span></code> attribute to make sure it is displayed almost invisibly in the tactic state, simply by a <code class="docutils literal notranslate"><span class="pre">↑</span></code> prefix.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">H</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">CoeFun</span><span class="w"> </span><span class="o">(</span><span class="n">MonoidHom₁</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="n">H</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">H</span><span class="o">)</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">coe</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">MonoidHom₁.toFun</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">G</span><span class="o">]</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">H</span><span class="o">]</span> <span class="o">:</span> <span class="n">CoeFun</span> <span class="o">(</span><span class="n">MonoidHom₁</span> <span class="n">G</span> <span class="n">H</span><span class="o">)</span> <span class="o">(</span><span class="k">fun</span> <span class="n">_</span> <span class="bp">↦</span> <span class="n">G</span> <span class="bp">→</span> <span class="n">H</span><span class="o">)</span> <span class="n">where</span> <span class="n">coe</span> <span class="o">:=</span> <span class="n">MonoidHom₁.toFun</span> <span class="kn">attribute</span><span class="w"> </span><span class="o">[</span><span class="n">coe</span><span class="o">]</span><span class="w"> </span><span class="n">MonoidHom₁.toFun</span> <span class="kn">attribute</span> <span class="o">[</span><span class="n">coe</span><span class="o">]</span> <span class="n">MonoidHom₁.toFun</span> </pre></div> </div> <p>Let us check we can indeed apply a bundled monoid morphism to an element.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">H</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">MonoidHom₁</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="n">H</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">f.map_one</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">G</span><span class="o">]</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">H</span><span class="o">]</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">MonoidHom₁</span> <span class="n">G</span> <span class="n">H</span><span class="o">)</span> <span class="o">:</span> <span class="n">f</span> <span class="mi">1</span> <span class="bp">=</span> <span class="mi">1</span> <span class="o">:=</span> <span class="n">f.map_one</span> </pre></div> </div> <p>We can do the same with other kind of morphisms until we reach ring morphisms.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">@[</span><span class="n">ext</span><span class="kd">]</span> <span class="kd">structure</span><span class="w"> </span><span class="n">AddMonoidHom₁</span><span class="w"> </span><span class="o">(</span><span class="n">G</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">AddMonoid</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">AddMonoid</span><span class="w"> </span><span class="n">H</span><span class="o">]</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">toFun</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">H</span> <span class="w"> </span><span class="n">map_zero</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">toFun</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span> <span class="w"> </span><span class="n">map_add</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">g'</span><span class="o">,</span><span class="w"> </span><span class="n">toFun</span><span class="w"> </span><span class="o">(</span><span class="n">g</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">g'</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">toFun</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">toFun</span><span class="w"> </span><span class="n">g'</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">@[ext]</span> <span class="kd">structure</span> <span class="n">AddMonoidHom₁</span> <span class="o">(</span><span class="n">G</span> <span class="n">H</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="o">[</span><span class="n">AddMonoid</span> <span class="n">G</span><span class="o">]</span> <span class="o">[</span><span class="n">AddMonoid</span> <span class="n">H</span><span class="o">]</span> <span class="n">where</span> <span class="n">toFun</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">→</span> <span class="n">H</span> <span class="n">map_zero</span> <span class="o">:</span> <span class="n">toFun</span> <span class="mi">0</span> <span class="bp">=</span> <span class="mi">0</span> <span class="n">map_add</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">g</span> <span class="n">g'</span><span class="o">,</span> <span class="n">toFun</span> <span class="o">(</span><span class="n">g</span> <span class="bp">+</span> <span class="n">g'</span><span class="o">)</span> <span class="bp">=</span> <span class="n">toFun</span> <span class="n">g</span> <span class="bp">+</span> <span class="n">toFun</span> <span class="n">g'</span> <span class="kd">instance</span><span class="w"> </span><span class="o">[</span><span class="n">AddMonoid</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">AddMonoid</span><span class="w"> </span><span class="n">H</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">CoeFun</span><span class="w"> </span><span class="o">(</span><span class="n">AddMonoidHom₁</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="n">H</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">H</span><span class="o">)</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">coe</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">AddMonoidHom₁.toFun</span> <span class="kd">instance</span> <span class="o">[</span><span class="n">AddMonoid</span> <span class="n">G</span><span class="o">]</span> <span class="o">[</span><span class="n">AddMonoid</span> <span class="n">H</span><span class="o">]</span> <span class="o">:</span> <span class="n">CoeFun</span> <span class="o">(</span><span class="n">AddMonoidHom₁</span> <span class="n">G</span> <span class="n">H</span><span class="o">)</span> <span class="o">(</span><span class="k">fun</span> <span class="n">_</span> <span class="bp">↦</span> <span class="n">G</span> <span class="bp">→</span> <span class="n">H</span><span class="o">)</span> <span class="n">where</span> <span class="n">coe</span> <span class="o">:=</span> <span class="n">AddMonoidHom₁.toFun</span> <span class="kn">attribute</span><span class="w"> </span><span class="o">[</span><span class="n">coe</span><span class="o">]</span><span class="w"> </span><span class="n">AddMonoidHom₁.toFun</span> <span class="kn">attribute</span> <span class="o">[</span><span class="n">coe</span><span class="o">]</span> <span class="n">AddMonoidHom₁.toFun</span> <span class="kd">@[</span><span class="n">ext</span><span class="kd">]</span> <span class="kd">structure</span><span class="w"> </span><span class="n">RingHom₁</span><span class="w"> </span><span class="o">(</span><span class="n">R</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">Ring</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Ring</span><span class="w"> </span><span class="n">S</span><span class="o">]</span><span class="w"> </span><span class="kd">extends</span><span class="w"> </span><span class="n">MonoidHom₁</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="n">S</span><span class="o">,</span><span class="w"> </span><span class="n">AddMonoidHom₁</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="n">S</span> <span class="kd">@[ext]</span> <span class="kd">structure</span> <span class="n">RingHom₁</span> <span class="o">(</span><span class="n">R</span> <span class="n">S</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="o">[</span><span class="n">Ring</span> <span class="n">R</span><span class="o">]</span> <span class="o">[</span><span class="n">Ring</span> <span class="n">S</span><span class="o">]</span> <span class="kd">extends</span> <span class="n">MonoidHom₁</span> <span class="n">R</span> <span class="n">S</span><span class="o">,</span> <span class="n">AddMonoidHom₁</span> <span class="n">R</span> <span class="n">S</span> </pre></div> </div> <p>There are a couple of issues about this approach. A minor one is we don’t quite know where to put
-
@@ -722,16 +718,16 @@ Neither option is appealing so Mathlib uses a new hierarchy trick here. The ideaa type class for objects that are at least monoid morphisms, instantiate that class with both monoid morphisms and ring morphisms and use it to state every lemma. In the definition below, <code class="docutils literal notranslate"><span class="pre">F</span></code> could be <code class="docutils literal notranslate"><span class="pre">MonoidHom₁</span> <span class="pre">M</span> <span class="pre">N</span></code>, or <code class="docutils literal notranslate"><span class="pre">RingHom₁</span> <span class="pre">M</span> <span class="pre">N</span></code> if <code class="docutils literal notranslate"><span class="pre">M</span></code> and <code class="docutils literal notranslate"><span class="pre">N</span></code> have a ring structure.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span><span class="w"> </span><span class="n">MonoidHomClass₁</span><span class="w"> </span><span class="o">(</span><span class="n">F</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">M</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">N</span><span class="o">]</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">toFun</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">N</span> <span class="w"> </span><span class="n">map_one</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">F</span><span class="o">,</span><span class="w"> </span><span class="n">toFun</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span> <span class="w"> </span><span class="n">map_mul</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">g'</span><span class="o">,</span><span class="w"> </span><span class="n">toFun</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">g</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">g'</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">toFun</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">toFun</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g'</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span> <span class="n">MonoidHomClass₁</span> <span class="o">(</span><span class="n">F</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="o">(</span><span class="n">M</span> <span class="n">N</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">M</span><span class="o">]</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">N</span><span class="o">]</span> <span class="n">where</span> <span class="n">toFun</span> <span class="o">:</span> <span class="n">F</span> <span class="bp">→</span> <span class="n">M</span> <span class="bp">→</span> <span class="n">N</span> <span class="n">map_one</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">f</span> <span class="o">:</span> <span class="n">F</span><span class="o">,</span> <span class="n">toFun</span> <span class="n">f</span> <span class="mi">1</span> <span class="bp">=</span> <span class="mi">1</span> <span class="n">map_mul</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">f</span> <span class="n">g</span> <span class="n">g'</span><span class="o">,</span> <span class="n">toFun</span> <span class="n">f</span> <span class="o">(</span><span class="n">g</span> <span class="bp">*</span> <span class="n">g'</span><span class="o">)</span> <span class="bp">=</span> <span class="n">toFun</span> <span class="n">f</span> <span class="n">g</span> <span class="bp">*</span> <span class="n">toFun</span> <span class="n">f</span> <span class="n">g'</span> </pre></div> </div> <p>However there is a problem with the above implementation. We haven’t registered a coercion to function instance yet. Let us try to do it now.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">badInst</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">N</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">MonoidHomClass₁</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="n">N</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">CoeFun</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">N</span><span class="o">)</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">coe</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">MonoidHomClass₁.toFun</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">badInst</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">M</span><span class="o">]</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">N</span><span class="o">]</span> <span class="o">[</span><span class="n">MonoidHomClass₁</span> <span class="n">F</span> <span class="n">M</span> <span class="n">N</span><span class="o">]</span> <span class="o">:</span> <span class="n">CoeFun</span> <span class="n">F</span> <span class="o">(</span><span class="k">fun</span> <span class="n">_</span> <span class="bp">↦</span> <span class="n">M</span> <span class="bp">→</span> <span class="n">N</span><span class="o">)</span> <span class="n">where</span> <span class="n">coe</span> <span class="o">:=</span> <span class="n">MonoidHomClass₁.toFun</span> </pre></div> </div> <p>Making this an instance would be bad. When faced with something like <code class="docutils literal notranslate"><span class="pre">f</span> <span class="pre">x</span></code> where the type of <code class="docutils literal notranslate"><span class="pre">f</span></code>
-
@@ -749,41 +745,41 @@ replace <code class="docutils literal notranslate"><span class="pre">def</span>and <code class="docutils literal notranslate"><span class="pre">N</span></code>. This is done using the <code class="docutils literal notranslate"><span class="pre">outParam</span></code> function. This function is defined as the identity function, but is still recognized by the type class machinery and triggers the desired behavior. Hence we can retry defining our class, paying attention to the <code class="docutils literal notranslate"><span class="pre">outParam</span></code> function:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span><span class="w"> </span><span class="n">MonoidHomClass₂</span><span class="w"> </span><span class="o">(</span><span class="n">F</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">M</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">outParam</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">N</span><span class="o">]</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">toFun</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">N</span> <span class="w"> </span><span class="n">map_one</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">F</span><span class="o">,</span><span class="w"> </span><span class="n">toFun</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span> <span class="w"> </span><span class="n">map_mul</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">g'</span><span class="o">,</span><span class="w"> </span><span class="n">toFun</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">g</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">g'</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">toFun</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">toFun</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g'</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span> <span class="n">MonoidHomClass₂</span> <span class="o">(</span><span class="n">F</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="o">(</span><span class="n">M</span> <span class="n">N</span> <span class="o">:</span> <span class="n">outParam</span> <span class="kt">Type</span><span class="o">)</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">M</span><span class="o">]</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">N</span><span class="o">]</span> <span class="n">where</span> <span class="n">toFun</span> <span class="o">:</span> <span class="n">F</span> <span class="bp">→</span> <span class="n">M</span> <span class="bp">→</span> <span class="n">N</span> <span class="n">map_one</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">f</span> <span class="o">:</span> <span class="n">F</span><span class="o">,</span> <span class="n">toFun</span> <span class="n">f</span> <span class="mi">1</span> <span class="bp">=</span> <span class="mi">1</span> <span class="n">map_mul</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">f</span> <span class="n">g</span> <span class="n">g'</span><span class="o">,</span> <span class="n">toFun</span> <span class="n">f</span> <span class="o">(</span><span class="n">g</span> <span class="bp">*</span> <span class="n">g'</span><span class="o">)</span> <span class="bp">=</span> <span class="n">toFun</span> <span class="n">f</span> <span class="n">g</span> <span class="bp">*</span> <span class="n">toFun</span> <span class="n">f</span> <span class="n">g'</span> <span class="kd">instance</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">N</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">MonoidHomClass₂</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="n">N</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">CoeFun</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">N</span><span class="o">)</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">coe</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">MonoidHomClass₂.toFun</span> <span class="kd">instance</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">M</span><span class="o">]</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">N</span><span class="o">]</span> <span class="o">[</span><span class="n">MonoidHomClass₂</span> <span class="n">F</span> <span class="n">M</span> <span class="n">N</span><span class="o">]</span> <span class="o">:</span> <span class="n">CoeFun</span> <span class="n">F</span> <span class="o">(</span><span class="k">fun</span> <span class="n">_</span> <span class="bp">↦</span> <span class="n">M</span> <span class="bp">→</span> <span class="n">N</span><span class="o">)</span> <span class="n">where</span> <span class="n">coe</span> <span class="o">:=</span> <span class="n">MonoidHomClass₂.toFun</span> <span class="kn">attribute</span><span class="w"> </span><span class="o">[</span><span class="n">coe</span><span class="o">]</span><span class="w"> </span><span class="n">MonoidHomClass₂.toFun</span> <span class="kn">attribute</span> <span class="o">[</span><span class="n">coe</span><span class="o">]</span> <span class="n">MonoidHomClass₂.toFun</span> </pre></div> </div> <p>Now we can proceed with our plan to instantiate this class.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span><span class="w"> </span><span class="o">(</span><span class="n">M</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">N</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">MonoidHomClass₂</span><span class="w"> </span><span class="o">(</span><span class="n">MonoidHom₁</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="n">N</span><span class="o">)</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">toFun</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">MonoidHom₁.toFun</span> <span class="w"> </span><span class="n">map_one</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">f.map_one</span> <span class="w"> </span><span class="n">map_mul</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">f.map_mul</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span> <span class="o">(</span><span class="n">M</span> <span class="n">N</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">M</span><span class="o">]</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">N</span><span class="o">]</span> <span class="o">:</span> <span class="n">MonoidHomClass₂</span> <span class="o">(</span><span class="n">MonoidHom₁</span> <span class="n">M</span> <span class="n">N</span><span class="o">)</span> <span class="n">M</span> <span class="n">N</span> <span class="n">where</span> <span class="n">toFun</span> <span class="o">:=</span> <span class="n">MonoidHom₁.toFun</span> <span class="n">map_one</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">f</span> <span class="bp">↦</span> <span class="n">f.map_one</span> <span class="n">map_mul</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">f</span> <span class="bp">↦</span> <span class="n">f.map_mul</span> <span class="kd">instance</span><span class="w"> </span><span class="o">(</span><span class="n">R</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">Ring</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Ring</span><span class="w"> </span><span class="n">S</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">MonoidHomClass₂</span><span class="w"> </span><span class="o">(</span><span class="n">RingHom₁</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="n">S</span><span class="o">)</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">toFun</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">f.toMonoidHom₁.toFun</span> <span class="w"> </span><span class="n">map_one</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">f.toMonoidHom₁.map_one</span> <span class="w"> </span><span class="n">map_mul</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">f.toMonoidHom₁.map_mul</span> <span class="kd">instance</span> <span class="o">(</span><span class="n">R</span> <span class="n">S</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="o">[</span><span class="n">Ring</span> <span class="n">R</span><span class="o">]</span> <span class="o">[</span><span class="n">Ring</span> <span class="n">S</span><span class="o">]</span> <span class="o">:</span> <span class="n">MonoidHomClass₂</span> <span class="o">(</span><span class="n">RingHom₁</span> <span class="n">R</span> <span class="n">S</span><span class="o">)</span> <span class="n">R</span> <span class="n">S</span> <span class="n">where</span> <span class="n">toFun</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">f</span> <span class="bp">↦</span> <span class="n">f.toMonoidHom₁.toFun</span> <span class="n">map_one</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">f</span> <span class="bp">↦</span> <span class="n">f.toMonoidHom₁.map_one</span> <span class="n">map_mul</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">f</span> <span class="bp">↦</span> <span class="n">f.toMonoidHom₁.map_mul</span> </pre></div> </div> <p>As promised every lemma we prove about <code class="docutils literal notranslate"><span class="pre">f</span> <span class="pre">:</span> <span class="pre">F</span></code> assuming an instance of <code class="docutils literal notranslate"><span class="pre">MonoidHomClass₁</span> <span class="pre">F</span></code> will apply both to monoid morphisms and ring morphisms. Let us see an example lemma and check it applies to both situations.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">lemma</span><span class="w"> </span><span class="n">map_inv_of_inv</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">N</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">MonoidHomClass₂</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="n">N</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">F</span><span class="o">)</span><span class="w"> </span><span class="o">{</span><span class="n">m</span><span class="w"> </span><span class="n">m'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">M</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m</span><span class="bp">*</span><span class="n">m'</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">m'</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="bp">←</span><span class="w"> </span><span class="n">MonoidHomClass₂.map_mul</span><span class="o">,</span><span class="w"> </span><span class="n">h</span><span class="o">,</span><span class="w"> </span><span class="n">MonoidHomClass₂.map_one</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">lemma</span> <span class="n">map_inv_of_inv</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">M</span><span class="o">]</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">N</span><span class="o">]</span> <span class="o">[</span><span class="n">MonoidHomClass₂</span> <span class="n">F</span> <span class="n">M</span> <span class="n">N</span><span class="o">]</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">F</span><span class="o">)</span> <span class="o">{</span><span class="n">m</span> <span class="n">m'</span> <span class="o">:</span> <span class="n">M</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">m</span><span class="bp">*</span><span class="n">m'</span> <span class="bp">=</span> <span class="mi">1</span><span class="o">)</span> <span class="o">:</span> <span class="n">f</span> <span class="n">m</span> <span class="bp">*</span> <span class="n">f</span> <span class="n">m'</span> <span class="bp">=</span> <span class="mi">1</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="bp">←</span> <span class="n">MonoidHomClass₂.map_mul</span><span class="o">,</span> <span class="n">h</span><span class="o">,</span> <span class="n">MonoidHomClass₂.map_one</span><span class="o">]</span> <span class="kd">example</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">N</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">MonoidHom₁</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="n">N</span><span class="o">)</span><span class="w"> </span><span class="o">{</span><span class="n">m</span><span class="w"> </span><span class="n">m'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">M</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">m</span><span class="bp">*</span><span class="n">m'</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">m'</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span> <span class="n">map_inv_of_inv</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">h</span> <span class="kd">example</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">M</span><span class="o">]</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">N</span><span class="o">]</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">MonoidHom₁</span> <span class="n">M</span> <span class="n">N</span><span class="o">)</span> <span class="o">{</span><span class="n">m</span> <span class="n">m'</span> <span class="o">:</span> <span class="n">M</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">m</span><span class="bp">*</span><span class="n">m'</span> <span class="bp">=</span> <span class="mi">1</span><span class="o">)</span> <span class="o">:</span> <span class="n">f</span> <span class="n">m</span> <span class="bp">*</span> <span class="n">f</span> <span class="n">m'</span> <span class="bp">=</span> <span class="mi">1</span> <span class="o">:=</span> <span class="n">map_inv_of_inv</span> <span class="n">f</span> <span class="n">h</span> <span class="kd">example</span><span class="w"> </span><span class="o">[</span><span class="n">Ring</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Ring</span><span class="w"> </span><span class="n">S</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">RingHom₁</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="n">S</span><span class="o">)</span><span class="w"> </span><span class="o">{</span><span class="n">r</span><span class="w"> </span><span class="n">r'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">r</span><span class="bp">*</span><span class="n">r'</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">r'</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span> <span class="n">map_inv_of_inv</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">h</span> <span class="kd">example</span> <span class="o">[</span><span class="n">Ring</span> <span class="n">R</span><span class="o">]</span> <span class="o">[</span><span class="n">Ring</span> <span class="n">S</span><span class="o">]</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">RingHom₁</span> <span class="n">R</span> <span class="n">S</span><span class="o">)</span> <span class="o">{</span><span class="n">r</span> <span class="n">r'</span> <span class="o">:</span> <span class="n">R</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">r</span><span class="bp">*</span><span class="n">r'</span> <span class="bp">=</span> <span class="mi">1</span><span class="o">)</span> <span class="o">:</span> <span class="n">f</span> <span class="n">r</span> <span class="bp">*</span> <span class="n">f</span> <span class="n">r'</span> <span class="bp">=</span> <span class="mi">1</span> <span class="o">:=</span> <span class="n">map_inv_of_inv</span> <span class="n">f</span> <span class="n">h</span> </pre></div> </div> <p>At first sight, it may look like we got back to our old bad idea of making <code class="docutils literal notranslate"><span class="pre">MonoidHom₁</span></code> a class.
-
@@ -796,16 +792,16 @@ to record that this pattern is used only for functions with extra properties, mecoercion to functions should be injective. So Mathlib adds one more layer of abstraction with the base class <code class="docutils literal notranslate"><span class="pre">DFunLike</span></code> (where “DFun” stands for dependent function). Let us redefine our <code class="docutils literal notranslate"><span class="pre">MonoidHomClass</span></code> on top of this base layer.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span><span class="w"> </span><span class="n">MonoidHomClass₃</span><span class="w"> </span><span class="o">(</span><span class="n">F</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">M</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">outParam</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">N</span><span class="o">]</span><span class="w"> </span><span class="kd">extends</span> <span class="w"> </span><span class="n">DFunLike</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">N</span><span class="o">)</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">map_one</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">F</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span> <span class="w"> </span><span class="n">map_mul</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">F</span><span class="o">)</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">g'</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">g</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">g'</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g'</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span> <span class="n">MonoidHomClass₃</span> <span class="o">(</span><span class="n">F</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="o">(</span><span class="n">M</span> <span class="n">N</span> <span class="o">:</span> <span class="n">outParam</span> <span class="kt">Type</span><span class="o">)</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">M</span><span class="o">]</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">N</span><span class="o">]</span> <span class="kd">extends</span> <span class="n">DFunLike</span> <span class="n">F</span> <span class="n">M</span> <span class="o">(</span><span class="k">fun</span> <span class="n">_</span> <span class="bp">↦</span> <span class="n">N</span><span class="o">)</span> <span class="n">where</span> <span class="n">map_one</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">f</span> <span class="o">:</span> <span class="n">F</span><span class="o">,</span> <span class="n">f</span> <span class="mi">1</span> <span class="bp">=</span> <span class="mi">1</span> <span class="n">map_mul</span> <span class="o">:</span> <span class="bp">∀</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">F</span><span class="o">)</span> <span class="n">g</span> <span class="n">g'</span><span class="o">,</span> <span class="n">f</span> <span class="o">(</span><span class="n">g</span> <span class="bp">*</span> <span class="n">g'</span><span class="o">)</span> <span class="bp">=</span> <span class="n">f</span> <span class="n">g</span> <span class="bp">*</span> <span class="n">f</span> <span class="n">g'</span> <span class="kd">instance</span><span class="w"> </span><span class="o">(</span><span class="n">M</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">N</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">MonoidHomClass₃</span><span class="w"> </span><span class="o">(</span><span class="n">MonoidHom₁</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="n">N</span><span class="o">)</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">coe</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">MonoidHom₁.toFun</span> <span class="w"> </span><span class="n">coe_injective'</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">MonoidHom₁.ext</span> <span class="w"> </span><span class="n">map_one</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">MonoidHom₁.map_one</span> <span class="w"> </span><span class="n">map_mul</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">MonoidHom₁.map_mul</span> <span class="kd">instance</span> <span class="o">(</span><span class="n">M</span> <span class="n">N</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">M</span><span class="o">]</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">N</span><span class="o">]</span> <span class="o">:</span> <span class="n">MonoidHomClass₃</span> <span class="o">(</span><span class="n">MonoidHom₁</span> <span class="n">M</span> <span class="n">N</span><span class="o">)</span> <span class="n">M</span> <span class="n">N</span> <span class="n">where</span> <span class="n">coe</span> <span class="o">:=</span> <span class="n">MonoidHom₁.toFun</span> <span class="n">coe_injective'</span> <span class="n">_</span> <span class="n">_</span> <span class="o">:=</span> <span class="n">MonoidHom₁.ext</span> <span class="n">map_one</span> <span class="o">:=</span> <span class="n">MonoidHom₁.map_one</span> <span class="n">map_mul</span> <span class="o">:=</span> <span class="n">MonoidHom₁.map_mul</span> </pre></div> </div> <p>Of course the hierarchy of morphisms does not stop here. We could go on and define a class
-
@@ -818,30 +814,30 @@ ordered types, and then order preserving monoid morphisms. This is for trainingLike continuous functions, order preserving functions are primarily unbundled in Mathlib where they are defined by the <code class="docutils literal notranslate"><span class="pre">Monotone</span></code> predicate. Of course you need to complete the class definitions below.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">@[</span><span class="n">ext</span><span class="kd">]</span> <span class="kd">structure</span><span class="w"> </span><span class="n">OrderPresHom</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="n">β</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">LE</span><span class="w"> </span><span class="n">α</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">LE</span><span class="w"> </span><span class="n">β</span><span class="o">]</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">toFun</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">β</span> <span class="w"> </span><span class="n">le_of_le</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">a'</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">a'</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">toFun</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">toFun</span><span class="w"> </span><span class="n">a'</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">@[ext]</span> <span class="kd">structure</span> <span class="n">OrderPresHom</span> <span class="o">(</span><span class="n">α</span> <span class="n">β</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="o">[</span><span class="n">LE</span> <span class="n">α</span><span class="o">]</span> <span class="o">[</span><span class="n">LE</span> <span class="n">β</span><span class="o">]</span> <span class="n">where</span> <span class="n">toFun</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">β</span> <span class="n">le_of_le</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span> <span class="n">a'</span><span class="o">,</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">a'</span> <span class="bp">→</span> <span class="n">toFun</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">toFun</span> <span class="n">a'</span> <span class="kd">@[</span><span class="n">ext</span><span class="kd">]</span> <span class="kd">structure</span><span class="w"> </span><span class="n">OrderPresMonoidHom</span><span class="w"> </span><span class="o">(</span><span class="n">M</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">LE</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">N</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">LE</span><span class="w"> </span><span class="n">N</span><span class="o">]</span><span class="w"> </span><span class="kd">extends</span> <span class="n">MonoidHom₁</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="n">N</span><span class="o">,</span><span class="w"> </span><span class="n">OrderPresHom</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="n">N</span> <span class="kd">@[ext]</span> <span class="kd">structure</span> <span class="n">OrderPresMonoidHom</span> <span class="o">(</span><span class="n">M</span> <span class="n">N</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">M</span><span class="o">]</span> <span class="o">[</span><span class="n">LE</span> <span class="n">M</span><span class="o">]</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">N</span><span class="o">]</span> <span class="o">[</span><span class="n">LE</span> <span class="n">N</span><span class="o">]</span> <span class="kd">extends</span> <span class="n">MonoidHom₁</span> <span class="n">M</span> <span class="n">N</span><span class="o">,</span> <span class="n">OrderPresHom</span> <span class="n">M</span> <span class="n">N</span> <span class="kd">class</span><span class="w"> </span><span class="n">OrderPresHomClass</span><span class="w"> </span><span class="o">(</span><span class="n">F</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="n">β</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">outParam</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">LE</span><span class="w"> </span><span class="n">α</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">LE</span><span class="w"> </span><span class="n">β</span><span class="o">]</span> <span class="kd">class</span> <span class="n">OrderPresHomClass</span> <span class="o">(</span><span class="n">F</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="o">(</span><span class="n">α</span> <span class="n">β</span> <span class="o">:</span> <span class="n">outParam</span> <span class="kt">Type</span><span class="o">)</span> <span class="o">[</span><span class="n">LE</span> <span class="n">α</span><span class="o">]</span> <span class="o">[</span><span class="n">LE</span> <span class="n">β</span><span class="o">]</span> <span class="kd">instance</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="n">β</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">LE</span><span class="w"> </span><span class="n">α</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">LE</span><span class="w"> </span><span class="n">β</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">OrderPresHomClass</span><span class="w"> </span><span class="o">(</span><span class="n">OrderPresHom</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="n">β</span><span class="o">)</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="n">β</span><span class="w"> </span><span class="n">where</span> <span class="kd">instance</span> <span class="o">(</span><span class="n">α</span> <span class="n">β</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="o">[</span><span class="n">LE</span> <span class="n">α</span><span class="o">]</span> <span class="o">[</span><span class="n">LE</span> <span class="n">β</span><span class="o">]</span> <span class="o">:</span> <span class="n">OrderPresHomClass</span> <span class="o">(</span><span class="n">OrderPresHom</span> <span class="n">α</span> <span class="n">β</span><span class="o">)</span> <span class="n">α</span> <span class="n">β</span> <span class="n">where</span> <span class="kd">instance</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="n">β</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">LE</span><span class="w"> </span><span class="n">α</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">α</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">LE</span><span class="w"> </span><span class="n">β</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">β</span><span class="o">]</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">OrderPresHomClass</span><span class="w"> </span><span class="o">(</span><span class="n">OrderPresMonoidHom</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="n">β</span><span class="o">)</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="n">β</span><span class="w"> </span><span class="n">where</span> <span class="kd">instance</span> <span class="o">(</span><span class="n">α</span> <span class="n">β</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="o">[</span><span class="n">LE</span> <span class="n">α</span><span class="o">]</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">α</span><span class="o">]</span> <span class="o">[</span><span class="n">LE</span> <span class="n">β</span><span class="o">]</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">β</span><span class="o">]</span> <span class="o">:</span> <span class="n">OrderPresHomClass</span> <span class="o">(</span><span class="n">OrderPresMonoidHom</span> <span class="n">α</span> <span class="n">β</span><span class="o">)</span> <span class="n">α</span> <span class="n">β</span> <span class="n">where</span> <span class="kd">instance</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="n">β</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">LE</span><span class="w"> </span><span class="n">α</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">α</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">LE</span><span class="w"> </span><span class="n">β</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">β</span><span class="o">]</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">MonoidHomClass₃</span><span class="w"> </span><span class="o">(</span><span class="n">OrderPresMonoidHom</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="n">β</span><span class="o">)</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="n">β</span> <span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <span class="kd">instance</span> <span class="o">(</span><span class="n">α</span> <span class="n">β</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="o">[</span><span class="n">LE</span> <span class="n">α</span><span class="o">]</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">α</span><span class="o">]</span> <span class="o">[</span><span class="n">LE</span> <span class="n">β</span><span class="o">]</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">β</span><span class="o">]</span> <span class="o">:</span> <span class="n">MonoidHomClass₃</span> <span class="o">(</span><span class="n">OrderPresMonoidHom</span> <span class="n">α</span> <span class="n">β</span><span class="o">)</span> <span class="n">α</span> <span class="n">β</span> <span class="o">:=</span> <span class="gr">sorry</span> </pre></div> </div> </section> <section id="sub-objects"> <span id="section-hierarchies-subobjects"></span><h2><span class="section-number">7.3. </span>Sub-objects<a class="headerlink" href="#sub-objects" title="Link to this heading"></a></h2> <span id="section-hierarchies-subobjects"></span><h2><span class="section-number">7.3. </span>Sub-objects<a class="headerlink" href="#sub-objects" title="Permalink to this heading"></a></h2> <p>After defining some algebraic structure and its morphisms, the next step is to consider sets that inherit this algebraic structure, for instance subgroups or subrings. This largely overlaps with our previous topic. Indeed a set in <code class="docutils literal notranslate"><span class="pre">X</span></code> is implemented as a function from
-
@@ -851,66 +847,66 @@ We won’t reuse <code class="docutils literal notranslate"><span class="preto <code class="docutils literal notranslate"><span class="pre">X</span> <span class="pre">→</span> <span class="pre">Prop</span></code>. Instead there is a <code class="docutils literal notranslate"><span class="pre">SetLike</span></code> class. Instead of wrapping an injection into a function type, that class wraps an injection into a <code class="docutils literal notranslate"><span class="pre">Set</span></code> type and defines the corresponding coercion and <code class="docutils literal notranslate"><span class="pre">Membership</span></code> instance.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">@[</span><span class="n">ext</span><span class="kd">]</span> <span class="kd">structure</span><span class="w"> </span><span class="n">Submonoid₁</span><span class="w"> </span><span class="o">(</span><span class="n">M</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="sd">/-- The carrier of a submonoid. -/</span> <span class="w"> </span><span class="n">carrier</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">M</span> <span class="w"> </span><span class="sd">/-- The product of two elements of a submonoid belongs to the submonoid. -/</span> <span class="w"> </span><span class="n">mul_mem</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="o">}</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">carrier</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">carrier</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">carrier</span> <span class="w"> </span><span class="sd">/-- The unit element belongs to the submonoid. -/</span> <span class="w"> </span><span class="n">one_mem</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">carrier</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">@[ext]</span> <span class="kd">structure</span> <span class="n">Submonoid₁</span> <span class="o">(</span><span class="n">M</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">M</span><span class="o">]</span> <span class="n">where</span> <span class="sd">/-- The carrier of a submonoid. -/</span> <span class="n">carrier</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">M</span> <span class="sd">/-- The product of two elements of a submonoid belongs to the submonoid. -/</span> <span class="n">mul_mem</span> <span class="o">{</span><span class="n">a</span> <span class="n">b</span><span class="o">}</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">∈</span> <span class="n">carrier</span> <span class="bp">→</span> <span class="n">b</span> <span class="bp">∈</span> <span class="n">carrier</span> <span class="bp">→</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">b</span> <span class="bp">∈</span> <span class="n">carrier</span> <span class="sd">/-- The unit element belongs to the submonoid. -/</span> <span class="n">one_mem</span> <span class="o">:</span> <span class="mi">1</span> <span class="bp">∈</span> <span class="n">carrier</span> <span class="sd">/-- Submonoids in `M` can be seen as sets in `M`. -/</span> <span class="kd">instance</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">SetLike</span><span class="w"> </span><span class="o">(</span><span class="n">Submonoid₁</span><span class="w"> </span><span class="n">M</span><span class="o">)</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">coe</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Submonoid₁.carrier</span> <span class="w"> </span><span class="n">coe_injective'</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Submonoid₁.ext</span> <span class="kd">instance</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">M</span><span class="o">]</span> <span class="o">:</span> <span class="n">SetLike</span> <span class="o">(</span><span class="n">Submonoid₁</span> <span class="n">M</span><span class="o">)</span> <span class="n">M</span> <span class="n">where</span> <span class="n">coe</span> <span class="o">:=</span> <span class="n">Submonoid₁.carrier</span> <span class="n">coe_injective'</span> <span class="n">_</span> <span class="n">_</span> <span class="o">:=</span> <span class="n">Submonoid₁.ext</span> </pre></div> </div> <p>Equipped with the above <code class="docutils literal notranslate"><span class="pre">SetLike</span></code> instance, we can already state naturally that a submonoid <code class="docutils literal notranslate"><span class="pre">N</span></code> contains <code class="docutils literal notranslate"><span class="pre">1</span></code> without using <code class="docutils literal notranslate"><span class="pre">N.carrier</span></code>. We can also silently treat <code class="docutils literal notranslate"><span class="pre">N</span></code> as a set in <code class="docutils literal notranslate"><span class="pre">M</span></code> as take its direct image under a map.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">N</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submonoid₁</span><span class="w"> </span><span class="n">M</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">N.one_mem</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">M</span><span class="o">]</span> <span class="o">(</span><span class="n">N</span> <span class="o">:</span> <span class="n">Submonoid₁</span> <span class="n">M</span><span class="o">)</span> <span class="o">:</span> <span class="mi">1</span> <span class="bp">∈</span> <span class="n">N</span> <span class="o">:=</span> <span class="n">N.one_mem</span> <span class="kd">example</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">N</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submonoid₁</span><span class="w"> </span><span class="n">M</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">α</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="n">N</span> <span class="kd">example</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">M</span><span class="o">]</span> <span class="o">(</span><span class="n">N</span> <span class="o">:</span> <span class="n">Submonoid₁</span> <span class="n">M</span><span class="o">)</span> <span class="o">(</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">M</span> <span class="bp">→</span> <span class="n">α</span><span class="o">)</span> <span class="o">:=</span> <span class="n">f</span> <span class="bp">''</span> <span class="n">N</span> </pre></div> </div> <p>We also have a coercion to <code class="docutils literal notranslate"><span class="pre">Type</span></code> which uses <code class="docutils literal notranslate"><span class="pre">Subtype</span></code> so, given a submonoid <code class="docutils literal notranslate"><span class="pre">N</span></code> we can write a parameter <code class="docutils literal notranslate"><span class="pre">(x</span> <span class="pre">:</span> <span class="pre">N)</span></code> which can be coerced to an element of <code class="docutils literal notranslate"><span class="pre">M</span></code> belonging to <code class="docutils literal notranslate"><span class="pre">N</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">N</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submonoid₁</span><span class="w"> </span><span class="n">M</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">N</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">M</span><span class="o">)</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">x.property</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">M</span><span class="o">]</span> <span class="o">(</span><span class="n">N</span> <span class="o">:</span> <span class="n">Submonoid₁</span> <span class="n">M</span><span class="o">)</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">N</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">M</span><span class="o">)</span> <span class="bp">∈</span> <span class="n">N</span> <span class="o">:=</span> <span class="n">x.property</span> </pre></div> </div> <p>Using this coercion to <code class="docutils literal notranslate"><span class="pre">Type</span></code> we can also tackle the task of equipping a submonoid with a monoid structure. We will use the coercion from the type associated to <code class="docutils literal notranslate"><span class="pre">N</span></code> as above, and the lemma <code class="docutils literal notranslate"><span class="pre">SetCoe.ext</span></code> asserting this coercion is injective. Both are provided by the <code class="docutils literal notranslate"><span class="pre">SetLike</span></code> instance.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span><span class="w"> </span><span class="n">SubMonoid₁Monoid</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">N</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submonoid₁</span><span class="w"> </span><span class="n">M</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Monoid</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">mul</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="o">⟨</span><span class="n">x</span><span class="bp">*</span><span class="n">y</span><span class="o">,</span><span class="w"> </span><span class="n">N.mul_mem</span><span class="w"> </span><span class="n">x.property</span><span class="w"> </span><span class="n">y.property</span><span class="o">⟩</span> <span class="w"> </span><span class="n">mul_assoc</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">SetCoe.ext</span><span class="w"> </span><span class="o">(</span><span class="n">mul_assoc</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">M</span><span class="o">)</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">z</span><span class="o">)</span> <span class="w"> </span><span class="n">one</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">⟨</span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="n">N.one_mem</span><span class="o">⟩</span> <span class="w"> </span><span class="n">one_mul</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">SetCoe.ext</span><span class="w"> </span><span class="o">(</span><span class="n">one_mul</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">M</span><span class="o">))</span> <span class="w"> </span><span class="n">mul_one</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">SetCoe.ext</span><span class="w"> </span><span class="o">(</span><span class="n">mul_one</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">M</span><span class="o">))</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span> <span class="n">SubMonoid₁Monoid</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">M</span><span class="o">]</span> <span class="o">(</span><span class="n">N</span> <span class="o">:</span> <span class="n">Submonoid₁</span> <span class="n">M</span><span class="o">)</span> <span class="o">:</span> <span class="n">Monoid</span> <span class="n">N</span> <span class="n">where</span> <span class="n">mul</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">x</span> <span class="n">y</span> <span class="bp">↦</span> <span class="o">⟨</span><span class="n">x</span><span class="bp">*</span><span class="n">y</span><span class="o">,</span> <span class="n">N.mul_mem</span> <span class="n">x.property</span> <span class="n">y.property</span><span class="o">⟩</span> <span class="n">mul_assoc</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">x</span> <span class="n">y</span> <span class="n">z</span> <span class="bp">↦</span> <span class="n">SetCoe.ext</span> <span class="o">(</span><span class="n">mul_assoc</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">M</span><span class="o">)</span> <span class="n">y</span> <span class="n">z</span><span class="o">)</span> <span class="n">one</span> <span class="o">:=</span> <span class="o">⟨</span><span class="mi">1</span><span class="o">,</span> <span class="n">N.one_mem</span><span class="o">⟩</span> <span class="n">one_mul</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">SetCoe.ext</span> <span class="o">(</span><span class="n">one_mul</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">M</span><span class="o">))</span> <span class="n">mul_one</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">SetCoe.ext</span> <span class="o">(</span><span class="n">mul_one</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">M</span><span class="o">))</span> </pre></div> </div> <p>Note that, in the above instance, instead of using the coercion to <code class="docutils literal notranslate"><span class="pre">M</span></code> and calling the <code class="docutils literal notranslate"><span class="pre">property</span></code> field, we could have used destructuring binders as follows.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">N</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submonoid₁</span><span class="w"> </span><span class="n">M</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Monoid</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">mul</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="o">⟨</span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">hx</span><span class="o">⟩</span><span class="w"> </span><span class="o">⟨</span><span class="n">y</span><span class="o">,</span><span class="w"> </span><span class="n">hy</span><span class="o">⟩</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="o">⟨</span><span class="n">x</span><span class="bp">*</span><span class="n">y</span><span class="o">,</span><span class="w"> </span><span class="n">N.mul_mem</span><span class="w"> </span><span class="n">hx</span><span class="w"> </span><span class="n">hy</span><span class="o">⟩</span> <span class="w"> </span><span class="n">mul_assoc</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="o">⟨</span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">_</span><span class="o">⟩</span><span class="w"> </span><span class="o">⟨</span><span class="n">y</span><span class="o">,</span><span class="w"> </span><span class="n">_</span><span class="o">⟩</span><span class="w"> </span><span class="o">⟨</span><span class="n">z</span><span class="o">,</span><span class="w"> </span><span class="n">_</span><span class="o">⟩</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">SetCoe.ext</span><span class="w"> </span><span class="o">(</span><span class="n">mul_assoc</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">z</span><span class="o">)</span> <span class="w"> </span><span class="n">one</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">⟨</span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="n">N.one_mem</span><span class="o">⟩</span> <span class="w"> </span><span class="n">one_mul</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="o">⟨</span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">_</span><span class="o">⟩</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">SetCoe.ext</span><span class="w"> </span><span class="o">(</span><span class="n">one_mul</span><span class="w"> </span><span class="n">x</span><span class="o">)</span> <span class="w"> </span><span class="n">mul_one</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="o">⟨</span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">_</span><span class="o">⟩</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">SetCoe.ext</span><span class="w"> </span><span class="o">(</span><span class="n">mul_one</span><span class="w"> </span><span class="n">x</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">M</span><span class="o">]</span> <span class="o">(</span><span class="n">N</span> <span class="o">:</span> <span class="n">Submonoid₁</span> <span class="n">M</span><span class="o">)</span> <span class="o">:</span> <span class="n">Monoid</span> <span class="n">N</span> <span class="n">where</span> <span class="n">mul</span> <span class="o">:=</span> <span class="k">fun</span> <span class="o">⟨</span><span class="n">x</span><span class="o">,</span> <span class="n">hx</span><span class="o">⟩</span> <span class="o">⟨</span><span class="n">y</span><span class="o">,</span> <span class="n">hy</span><span class="o">⟩</span> <span class="bp">↦</span> <span class="o">⟨</span><span class="n">x</span><span class="bp">*</span><span class="n">y</span><span class="o">,</span> <span class="n">N.mul_mem</span> <span class="n">hx</span> <span class="n">hy</span><span class="o">⟩</span> <span class="n">mul_assoc</span> <span class="o">:=</span> <span class="k">fun</span> <span class="o">⟨</span><span class="n">x</span><span class="o">,</span> <span class="n">_</span><span class="o">⟩</span> <span class="o">⟨</span><span class="n">y</span><span class="o">,</span> <span class="n">_</span><span class="o">⟩</span> <span class="o">⟨</span><span class="n">z</span><span class="o">,</span> <span class="n">_</span><span class="o">⟩</span> <span class="bp">↦</span> <span class="n">SetCoe.ext</span> <span class="o">(</span><span class="n">mul_assoc</span> <span class="n">x</span> <span class="n">y</span> <span class="n">z</span><span class="o">)</span> <span class="n">one</span> <span class="o">:=</span> <span class="o">⟨</span><span class="mi">1</span><span class="o">,</span> <span class="n">N.one_mem</span><span class="o">⟩</span> <span class="n">one_mul</span> <span class="o">:=</span> <span class="k">fun</span> <span class="o">⟨</span><span class="n">x</span><span class="o">,</span> <span class="n">_</span><span class="o">⟩</span> <span class="bp">↦</span> <span class="n">SetCoe.ext</span> <span class="o">(</span><span class="n">one_mul</span> <span class="n">x</span><span class="o">)</span> <span class="n">mul_one</span> <span class="o">:=</span> <span class="k">fun</span> <span class="o">⟨</span><span class="n">x</span><span class="o">,</span> <span class="n">_</span><span class="o">⟩</span> <span class="bp">↦</span> <span class="n">SetCoe.ext</span> <span class="o">(</span><span class="n">mul_one</span> <span class="n">x</span><span class="o">)</span> </pre></div> </div> <p>In order to apply lemmas about submonoids to subgroups or subrings, we need a class, just like for morphisms. Note this class take a <code class="docutils literal notranslate"><span class="pre">SetLike</span></code> instance as a parameter so it does not need a carrier field and can use the membership notation in its fields.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span><span class="w"> </span><span class="n">SubmonoidClass₁</span><span class="w"> </span><span class="o">(</span><span class="n">S</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">M</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">SetLike</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Prop</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">mul_mem</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">S</span><span class="o">)</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">M</span><span class="o">},</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span> <span class="w"> </span><span class="n">one_mem</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">S</span><span class="o">,</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">class</span> <span class="n">SubmonoidClass₁</span> <span class="o">(</span><span class="n">S</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="o">(</span><span class="n">M</span> <span class="o">:</span> <span class="kt">Type</span><span class="o">)</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">M</span><span class="o">]</span> <span class="o">[</span><span class="n">SetLike</span> <span class="n">S</span> <span class="n">M</span><span class="o">]</span> <span class="o">:</span> <span class="kt">Prop</span> <span class="n">where</span> <span class="n">mul_mem</span> <span class="o">:</span> <span class="bp">∀</span> <span class="o">(</span><span class="n">s</span> <span class="o">:</span> <span class="n">S</span><span class="o">)</span> <span class="o">{</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">M</span><span class="o">},</span> <span class="n">a</span> <span class="bp">∈</span> <span class="n">s</span> <span class="bp">→</span> <span class="n">b</span> <span class="bp">∈</span> <span class="n">s</span> <span class="bp">→</span> <span class="n">a</span> <span class="bp">*</span> <span class="n">b</span> <span class="bp">∈</span> <span class="n">s</span> <span class="n">one_mem</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">s</span> <span class="o">:</span> <span class="n">S</span><span class="o">,</span> <span class="mi">1</span> <span class="bp">∈</span> <span class="n">s</span> <span class="kd">instance</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">SubmonoidClass₁</span><span class="w"> </span><span class="o">(</span><span class="n">Submonoid₁</span><span class="w"> </span><span class="n">M</span><span class="o">)</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">mul_mem</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Submonoid₁.mul_mem</span> <span class="w"> </span><span class="n">one_mem</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Submonoid₁.one_mem</span> <span class="kd">instance</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">M</span><span class="o">]</span> <span class="o">:</span> <span class="n">SubmonoidClass₁</span> <span class="o">(</span><span class="n">Submonoid₁</span> <span class="n">M</span><span class="o">)</span> <span class="n">M</span> <span class="n">where</span> <span class="n">mul_mem</span> <span class="o">:=</span> <span class="n">Submonoid₁.mul_mem</span> <span class="n">one_mem</span> <span class="o">:=</span> <span class="n">Submonoid₁.one_mem</span> </pre></div> </div> <p>As an exercise you should define a <code class="docutils literal notranslate"><span class="pre">Subgroup₁</span></code> structure, endow it with a <code class="docutils literal notranslate"><span class="pre">SetLike</span></code> instance
-
@@ -920,15 +916,15 @@ and a <code class="docutils literal notranslate"><span class="pre">SubmonoidClasalways form a complete lattice, and this structure is used a lot. For instance you may look for the lemma saying that an intersection of submonoids is a submonoid. But this won’t be a lemma, this will be an infimum construction. Let us do the case of two submonoids.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Inf</span><span class="w"> </span><span class="o">(</span><span class="n">Submonoid₁</span><span class="w"> </span><span class="n">M</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">⟨</span><span class="k">fun</span><span class="w"> </span><span class="n">S₁</span><span class="w"> </span><span class="n">S₂</span><span class="w"> </span><span class="bp">↦</span> <span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">carrier</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">S₁</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">S₂</span> <span class="w"> </span><span class="n">one_mem</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">⟨</span><span class="n">S₁.one_mem</span><span class="o">,</span><span class="w"> </span><span class="n">S₂.one_mem</span><span class="o">⟩</span> <span class="w"> </span><span class="n">mul_mem</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="o">⟨</span><span class="n">hx</span><span class="o">,</span><span class="w"> </span><span class="n">hx'</span><span class="o">⟩</span><span class="w"> </span><span class="o">⟨</span><span class="n">hy</span><span class="o">,</span><span class="w"> </span><span class="n">hy'</span><span class="o">⟩</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="o">⟨</span><span class="n">S₁.mul_mem</span><span class="w"> </span><span class="n">hx</span><span class="w"> </span><span class="n">hy</span><span class="o">,</span><span class="w"> </span><span class="n">S₂.mul_mem</span><span class="w"> </span><span class="n">hx'</span><span class="w"> </span><span class="n">hy'</span><span class="o">⟩</span><span class="w"> </span><span class="o">}⟩</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">instance</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">M</span><span class="o">]</span> <span class="o">:</span> <span class="n">Inf</span> <span class="o">(</span><span class="n">Submonoid₁</span> <span class="n">M</span><span class="o">)</span> <span class="o">:=</span> <span class="o">⟨</span><span class="k">fun</span> <span class="n">S₁</span> <span class="n">S₂</span> <span class="bp">↦</span> <span class="o">{</span> <span class="n">carrier</span> <span class="o">:=</span> <span class="n">S₁</span> <span class="bp">∩</span> <span class="n">S₂</span> <span class="n">one_mem</span> <span class="o">:=</span> <span class="o">⟨</span><span class="n">S₁.one_mem</span><span class="o">,</span> <span class="n">S₂.one_mem</span><span class="o">⟩</span> <span class="n">mul_mem</span> <span class="o">:=</span> <span class="k">fun</span> <span class="o">⟨</span><span class="n">hx</span><span class="o">,</span> <span class="n">hx'</span><span class="o">⟩</span> <span class="o">⟨</span><span class="n">hy</span><span class="o">,</span> <span class="n">hy'</span><span class="o">⟩</span> <span class="bp">↦</span> <span class="o">⟨</span><span class="n">S₁.mul_mem</span> <span class="n">hx</span> <span class="n">hy</span><span class="o">,</span> <span class="n">S₂.mul_mem</span> <span class="n">hx'</span> <span class="n">hy'</span><span class="o">⟩</span> <span class="o">}⟩</span> </pre></div> </div> <p>This allows to get the intersections of two submonoids as a submonoid.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">N</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submonoid₁</span><span class="w"> </span><span class="n">M</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submonoid₁</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">P</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">M</span><span class="o">]</span> <span class="o">(</span><span class="n">N</span> <span class="n">P</span> <span class="o">:</span> <span class="n">Submonoid₁</span> <span class="n">M</span><span class="o">)</span> <span class="o">:</span> <span class="n">Submonoid₁</span> <span class="n">M</span> <span class="o">:=</span> <span class="n">N</span> <span class="bp">⊓</span> <span class="n">P</span> </pre></div> </div> <p>You may think it’s a shame that we had to use the inf symbol <code class="docutils literal notranslate"><span class="pre">⊓</span></code> in the above example instead
-
@@ -950,31 +946,31 @@ is the <code class="docutils literal notranslate"><span class="pre">HasQuotient<to you. In the last example, you can use <code class="docutils literal notranslate"><span class="pre">Setoid.refl</span></code> but it won’t automatically pick up the relevant <code class="docutils literal notranslate"><span class="pre">Setoid</span></code> structure. You can fix this issue by providing all arguments using the <code class="docutils literal notranslate"><span class="pre">@</span></code> syntax, as in <code class="docutils literal notranslate"><span class="pre">@Setoid.refl</span> <span class="pre">M</span> <span class="pre">N.Setoid</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">Submonoid.Setoid</span><span class="w"> </span><span class="o">[</span><span class="n">CommMonoid</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">N</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submonoid</span><span class="w"> </span><span class="n">M</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Setoid</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">w</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">N</span><span class="o">,</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">N</span><span class="o">,</span><span class="w"> </span><span class="n">x</span><span class="bp">*</span><span class="n">w</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">y</span><span class="bp">*</span><span class="n">z</span> <span class="w"> </span><span class="n">iseqv</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">{</span> <span class="w"> </span><span class="n">refl</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="o">⟨</span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="n">N.one_mem</span><span class="o">,</span><span class="w"> </span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="n">N.one_mem</span><span class="o">,</span><span class="w"> </span><span class="n">rfl</span><span class="o">⟩</span> <span class="w"> </span><span class="n">symm</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="o">⟨</span><span class="n">w</span><span class="o">,</span><span class="w"> </span><span class="n">hw</span><span class="o">,</span><span class="w"> </span><span class="n">z</span><span class="o">,</span><span class="w"> </span><span class="n">hz</span><span class="o">,</span><span class="w"> </span><span class="n">h</span><span class="o">⟩</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="o">⟨</span><span class="n">z</span><span class="o">,</span><span class="w"> </span><span class="n">hz</span><span class="o">,</span><span class="w"> </span><span class="n">w</span><span class="o">,</span><span class="w"> </span><span class="n">hw</span><span class="o">,</span><span class="w"> </span><span class="n">h.symm</span><span class="o">⟩</span> <span class="w"> </span><span class="n">trans</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="o">}</span> <span class="kd">instance</span><span class="w"> </span><span class="o">[</span><span class="n">CommMonoid</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">HasQuotient</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="o">(</span><span class="n">Submonoid</span><span class="w"> </span><span class="n">M</span><span class="o">)</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">quotient'</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">Quotient</span><span class="w"> </span><span class="n">N.Setoid</span> <span class="kd">def</span><span class="w"> </span><span class="n">QuotientMonoid.mk</span><span class="w"> </span><span class="o">[</span><span class="n">CommMonoid</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">N</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submonoid</span><span class="w"> </span><span class="n">M</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Quotient.mk</span><span class="w"> </span><span class="n">N.Setoid</span> <span class="kd">instance</span><span class="w"> </span><span class="o">[</span><span class="n">CommMonoid</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">N</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submonoid</span><span class="w"> </span><span class="n">M</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Monoid</span><span class="w"> </span><span class="o">(</span><span class="n">M</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="n">N</span><span class="o">)</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">mul</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Quotient.map₂'</span><span class="w"> </span><span class="o">(</span><span class="bp">·</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="bp">·</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="o">)</span> <span class="w"> </span><span class="n">mul_assoc</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">one</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">QuotientMonoid.mk</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="mi">1</span> <span class="w"> </span><span class="n">one_mul</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">mul_one</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">Submonoid.Setoid</span> <span class="o">[</span><span class="n">CommMonoid</span> <span class="n">M</span><span class="o">]</span> <span class="o">(</span><span class="n">N</span> <span class="o">:</span> <span class="n">Submonoid</span> <span class="n">M</span><span class="o">)</span> <span class="o">:</span> <span class="n">Setoid</span> <span class="n">M</span> <span class="n">where</span> <span class="n">r</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">x</span> <span class="n">y</span> <span class="bp">↦</span> <span class="bp">∃</span> <span class="n">w</span> <span class="bp">∈</span> <span class="n">N</span><span class="o">,</span> <span class="bp">∃</span> <span class="n">z</span> <span class="bp">∈</span> <span class="n">N</span><span class="o">,</span> <span class="n">x</span><span class="bp">*</span><span class="n">w</span> <span class="bp">=</span> <span class="n">y</span><span class="bp">*</span><span class="n">z</span> <span class="n">iseqv</span> <span class="o">:=</span> <span class="o">{</span> <span class="n">refl</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="o">⟨</span><span class="mi">1</span><span class="o">,</span> <span class="n">N.one_mem</span><span class="o">,</span> <span class="mi">1</span><span class="o">,</span> <span class="n">N.one_mem</span><span class="o">,</span> <span class="n">rfl</span><span class="o">⟩</span> <span class="n">symm</span> <span class="o">:=</span> <span class="k">fun</span> <span class="o">⟨</span><span class="n">w</span><span class="o">,</span> <span class="n">hw</span><span class="o">,</span> <span class="n">z</span><span class="o">,</span> <span class="n">hz</span><span class="o">,</span> <span class="n">h</span><span class="o">⟩</span> <span class="bp">↦</span> <span class="o">⟨</span><span class="n">z</span><span class="o">,</span> <span class="n">hz</span><span class="o">,</span> <span class="n">w</span><span class="o">,</span> <span class="n">hw</span><span class="o">,</span> <span class="n">h.symm</span><span class="o">⟩</span> <span class="n">trans</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="o">}</span> <span class="kd">instance</span> <span class="o">[</span><span class="n">CommMonoid</span> <span class="n">M</span><span class="o">]</span> <span class="o">:</span> <span class="n">HasQuotient</span> <span class="n">M</span> <span class="o">(</span><span class="n">Submonoid</span> <span class="n">M</span><span class="o">)</span> <span class="n">where</span> <span class="n">quotient'</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">N</span> <span class="bp">↦</span> <span class="n">Quotient</span> <span class="n">N.Setoid</span> <span class="kd">def</span> <span class="n">QuotientMonoid.mk</span> <span class="o">[</span><span class="n">CommMonoid</span> <span class="n">M</span><span class="o">]</span> <span class="o">(</span><span class="n">N</span> <span class="o">:</span> <span class="n">Submonoid</span> <span class="n">M</span><span class="o">)</span> <span class="o">:</span> <span class="n">M</span> <span class="bp">→</span> <span class="n">M</span> <span class="bp">⧸</span> <span class="n">N</span> <span class="o">:=</span> <span class="n">Quotient.mk</span> <span class="n">N.Setoid</span> <span class="kd">instance</span> <span class="o">[</span><span class="n">CommMonoid</span> <span class="n">M</span><span class="o">]</span> <span class="o">(</span><span class="n">N</span> <span class="o">:</span> <span class="n">Submonoid</span> <span class="n">M</span><span class="o">)</span> <span class="o">:</span> <span class="n">Monoid</span> <span class="o">(</span><span class="n">M</span> <span class="bp">⧸</span> <span class="n">N</span><span class="o">)</span> <span class="n">where</span> <span class="n">mul</span> <span class="o">:=</span> <span class="n">Quotient.map₂'</span> <span class="o">(</span><span class="bp">·</span> <span class="bp">*</span> <span class="bp">·</span><span class="o">)</span> <span class="o">(</span><span class="kd">by</span> <span class="gr">sorry</span> <span class="o">)</span> <span class="n">mul_assoc</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="n">one</span> <span class="o">:=</span> <span class="n">QuotientMonoid.mk</span> <span class="n">N</span> <span class="mi">1</span> <span class="n">one_mul</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="n">mul_one</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> </section>
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-
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@@ -1,24 +1,24 @@<!DOCTYPE html> <html class="writer-html5" lang="en" data-content_root="./"> <html class="writer-html5" lang="en" > <head> <meta charset="utf-8" /><meta name="viewport" content="width=device-width, initial-scale=1" /> <meta charset="utf-8" /><meta name="generator" content="Docutils 0.17.1: http://docutils.sourceforge.net/" /> <meta name="viewport" content="width=device-width, initial-scale=1.0" /> <title>8. Groups and Rings — Mathematics in Lean 0.1 documentation</title> <link rel="stylesheet" type="text/css" href="_static/pygments.css?v=80d5e7a1" /> <link rel="stylesheet" type="text/css" href="_static/css/theme.css?v=e59714d7" /> <link rel="stylesheet" type="text/css" href="_static/css/custom.css?v=0731ccc3" /> <link rel="stylesheet" href="_static/pygments.css" type="text/css" /> <link rel="stylesheet" href="_static/css/theme.css" type="text/css" /> <link rel="stylesheet" href="_static/css/custom.css" type="text/css" /> <link rel="shortcut icon" href="_static/favicon.ico"/> <script src="_static/jquery.js?v=5d32c60e"></script> <script src="_static/_sphinx_javascript_frameworks_compat.js?v=2cd50e6c"></script> <script src="_static/documentation_options.js?v=2709fde1"></script> <script src="_static/doctools.js?v=9bcbadda"></script> <script src="_static/sphinx_highlight.js?v=dc90522c"></script> <script async="async" src="https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js"></script> <!--[if lt IE 9]> <script src="_static/js/html5shiv.min.js"></script> <![endif]--> <script data-url_root="./" id="documentation_options" src="_static/documentation_options.js"></script> <script src="_static/jquery.js"></script> <script src="_static/underscore.js"></script> <script src="_static/_sphinx_javascript_frameworks_compat.js"></script> <script src="_static/doctools.js"></script> <script async="async" src="https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js"></script> <script src="_static/js/theme.js"></script> <link rel="index" title="Index" href="genindex.html" /> <link rel="search" title="Search" href="search.html" />
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@@ -31,15 +31,11 @@<nav data-toggle="wy-nav-shift" class="wy-nav-side"> <div class="wy-side-scroll"> <div class="wy-side-nav-search" > <a href="index.html" class="icon icon-home"> Mathematics in Lean <a href="index.html" class="icon icon-home"> Mathematics in Lean </a> <div role="search"> <form id="rtd-search-form" class="wy-form" action="search.html" method="get"> <input type="text" name="q" placeholder="Search docs" aria-label="Search docs" /> <input type="text" name="q" placeholder="Search docs" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form>
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@@ -93,8 +89,8 @@<div class="rst-content"> <div role="navigation" aria-label="Page navigation"> <ul class="wy-breadcrumbs"> <li><a href="index.html" class="icon icon-home" aria-label="Home"></a></li> <li class="breadcrumb-item active"><span class="section-number">8. </span>Groups and Rings</li> <li><a href="index.html" class="icon icon-home"></a> »</li> <li><span class="section-number">8. </span>Groups and Rings</li> <li class="wy-breadcrumbs-aside"> <a href="_sources/C08_Groups_and_Rings.rst.txt" rel="nofollow"> View page source</a> </li>
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@@ -105,7 +101,7 @@<div itemprop="articleBody"> <section id="groups-and-rings"> <span id="groups-and-ring"></span><h1><span class="section-number">8. </span>Groups and Rings<a class="headerlink" href="#groups-and-rings" title="Link to this heading"></a></h1> <span id="groups-and-ring"></span><h1><span class="section-number">8. </span>Groups and Rings<a class="headerlink" href="#groups-and-rings" title="Permalink to this heading"></a></h1> <p>We saw in <a class="reference internal" href="C02_Basics.html#proving-identities-in-algebraic-structures"><span class="std std-numref">Section 2.2</span></a> how to reason about operations in groups and rings. Later, in <a class="reference internal" href="C06_Structures.html#section-algebraic-structures"><span class="std std-numref">Section 6.2</span></a>, we saw how to define abstract algebraic structures, such as group structures, as well as concrete instances
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@@ -120,9 +116,9 @@ decisions behind the way the topics are treated.So making sense of some of the examples may require reviewing the background from <a class="reference internal" href="C07_Hierarchies.html#hierarchies"><span class="std std-numref">Chapter 7</span></a>.</p> <section id="monoids-and-groups"> <span id="groups"></span><h2><span class="section-number">8.1. </span>Monoids and Groups<a class="headerlink" href="#monoids-and-groups" title="Link to this heading"></a></h2> <section id="monoids-and-their-morphisms"> <span id="index-1"></span><span id="index-0"></span><h3><span class="section-number">8.1.1. </span>Monoids and their morphisms<a class="headerlink" href="#monoids-and-their-morphisms" title="Link to this heading"></a></h3> <span id="groups"></span><h2><span class="section-number">8.1. </span>Monoids and Groups<a class="headerlink" href="#monoids-and-groups" title="Permalink to this heading"></a></h2> <span class="target" id="index-0"></span><section id="monoids-and-their-morphisms"> <span id="index-1"></span><h3><span class="section-number">8.1.1. </span>Monoids and their morphisms<a class="headerlink" href="#monoids-and-their-morphisms" title="Permalink to this heading"></a></h3> <p>Courses in abstract algebra often start with groups and then progress to rings, fields, and vector spaces. This involves some contortions when discussing multiplication on rings since the multiplication operation does not come from a group structure
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@@ -144,9 +140,9 @@ argument (in other words, in square brackets).By default, <code class="docutils literal notranslate"><span class="pre">Monoid</span></code> uses multiplicative notation for the operation; for additive notation use <code class="docutils literal notranslate"><span class="pre">AddMonoid</span></code> instead. The commutative versions of these structures add the prefix <code class="docutils literal notranslate"><span class="pre">Comm</span></code> before <code class="docutils literal notranslate"><span class="pre">Monoid</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">M</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">M</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">mul_one</span><span class="w"> </span><span class="n">x</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">M</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">M</span><span class="o">]</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">M</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">*</span> <span class="mi">1</span> <span class="bp">=</span> <span class="n">x</span> <span class="o">:=</span> <span class="n">mul_one</span> <span class="n">x</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">M</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">AddCommMonoid</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">M</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">add_comm</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span> <span class="kd">example</span> <span class="o">{</span><span class="n">M</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">AddCommMonoid</span> <span class="n">M</span><span class="o">]</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">M</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">y</span> <span class="bp">=</span> <span class="n">y</span> <span class="bp">+</span> <span class="n">x</span> <span class="o">:=</span> <span class="n">add_comm</span> <span class="n">x</span> <span class="n">y</span> </pre></div> </div> <p>Note that although <code class="docutils literal notranslate"><span class="pre">AddMonoid</span></code> is found in the library,
-
@@ -155,51 +151,51 @@ it is generally confusing to use additive notation with a non-commutative operat<code class="docutils literal notranslate"><span class="pre">M</span> <span class="pre">→*</span> <span class="pre">N</span></code>. Lean will automatically see such a morphism as a function from <code class="docutils literal notranslate"><span class="pre">M</span></code> to <code class="docutils literal notranslate"><span class="pre">N</span></code> when we apply it to elements of <code class="docutils literal notranslate"><span class="pre">M</span></code>. The additive version is called <code class="docutils literal notranslate"><span class="pre">AddMonoidHom</span></code> and written <code class="docutils literal notranslate"><span class="pre">M</span> <span class="pre">→+</span> <span class="pre">N</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">M</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">N</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">M</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="bp">→*</span><span class="w"> </span><span class="n">N</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">f.map_mul</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">M</span> <span class="n">N</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">M</span><span class="o">]</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">N</span><span class="o">]</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">M</span><span class="o">)</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">M</span> <span class="bp">→*</span> <span class="n">N</span><span class="o">)</span> <span class="o">:</span> <span class="n">f</span> <span class="o">(</span><span class="n">x</span> <span class="bp">*</span> <span class="n">y</span><span class="o">)</span> <span class="bp">=</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">*</span> <span class="n">f</span> <span class="n">y</span> <span class="o">:=</span> <span class="n">f.map_mul</span> <span class="n">x</span> <span class="n">y</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">M</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">AddMonoid</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">AddMonoid</span><span class="w"> </span><span class="n">N</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="bp">→+</span><span class="w"> </span><span class="n">N</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">f.map_zero</span> <span class="kd">example</span> <span class="o">{</span><span class="n">M</span> <span class="n">N</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">AddMonoid</span> <span class="n">M</span><span class="o">]</span> <span class="o">[</span><span class="n">AddMonoid</span> <span class="n">N</span><span class="o">]</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">M</span> <span class="bp">→+</span> <span class="n">N</span><span class="o">)</span> <span class="o">:</span> <span class="n">f</span> <span class="mi">0</span> <span class="bp">=</span> <span class="mi">0</span> <span class="o">:=</span> <span class="n">f.map_zero</span> </pre></div> </div> <p>These morphisms are bundled maps, i.e. they package together a map and some of its properties. Remember that <a class="reference internal" href="C07_Hierarchies.html#section-hierarchies-morphisms"><span class="std std-numref">Section 7.2</span></a> explains bundled maps; here we simply note the slightly unfortunate consequence that we cannot use ordinary function composition to compose maps. Instead, we need to use <code class="docutils literal notranslate"><span class="pre">MonoidHom.comp</span></code> and <code class="docutils literal notranslate"><span class="pre">AddMonoidHom.comp</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">M</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">AddMonoid</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">AddMonoid</span><span class="w"> </span><span class="n">N</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">AddMonoid</span><span class="w"> </span><span class="n">P</span><span class="o">]</span> <span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="bp">→+</span><span class="w"> </span><span class="n">N</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">g</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="bp">→+</span><span class="w"> </span><span class="n">P</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="bp">→+</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">g.comp</span><span class="w"> </span><span class="n">f</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">M</span> <span class="n">N</span> <span class="n">P</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">AddMonoid</span> <span class="n">M</span><span class="o">]</span> <span class="o">[</span><span class="n">AddMonoid</span> <span class="n">N</span><span class="o">]</span> <span class="o">[</span><span class="n">AddMonoid</span> <span class="n">P</span><span class="o">]</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">M</span> <span class="bp">→+</span> <span class="n">N</span><span class="o">)</span> <span class="o">(</span><span class="n">g</span> <span class="o">:</span> <span class="n">N</span> <span class="bp">→+</span> <span class="n">P</span><span class="o">)</span> <span class="o">:</span> <span class="n">M</span> <span class="bp">→+</span> <span class="n">P</span> <span class="o">:=</span> <span class="n">g.comp</span> <span class="n">f</span> </pre></div> </div> </section> <section id="groups-and-their-morphisms"> <h3><span class="section-number">8.1.2. </span>Groups and their morphisms<a class="headerlink" href="#groups-and-their-morphisms" title="Link to this heading"></a></h3> <h3><span class="section-number">8.1.2. </span>Groups and their morphisms<a class="headerlink" href="#groups-and-their-morphisms" title="Permalink to this heading"></a></h3> <p>We will have much more to say about groups, which are monoids with the extra property that every element has an inverse.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">x</span><span class="bp">⁻¹</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">mul_inv_cancel</span><span class="w"> </span><span class="n">x</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">G</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">*</span> <span class="n">x</span><span class="bp">⁻¹</span> <span class="bp">=</span> <span class="mi">1</span> <span class="o">:=</span> <span class="n">mul_inv_cancel</span> <span class="n">x</span> </pre></div> </div> <p id="index-2">Similar to the <code class="docutils literal notranslate"><span class="pre">ring</span></code> tactic that we saw earlier, there is a <code class="docutils literal notranslate"><span class="pre">group</span></code> tactic that proves any identity that holds in any group. (Equivalently, it proves the identities that hold in free groups.)</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">y</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">z</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">z</span><span class="o">)</span><span class="bp">⁻¹</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">x</span><span class="bp">⁻¹</span><span class="o">)</span><span class="bp">⁻¹</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">group</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="n">z</span> <span class="o">:</span> <span class="n">G</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">*</span> <span class="o">(</span><span class="n">y</span> <span class="bp">*</span> <span class="n">z</span><span class="o">)</span> <span class="bp">*</span> <span class="o">(</span><span class="n">x</span> <span class="bp">*</span> <span class="n">z</span><span class="o">)</span><span class="bp">⁻¹</span> <span class="bp">*</span> <span class="o">(</span><span class="n">x</span> <span class="bp">*</span> <span class="n">y</span> <span class="bp">*</span> <span class="n">x</span><span class="bp">⁻¹</span><span class="o">)</span><span class="bp">⁻¹</span> <span class="bp">=</span> <span class="mi">1</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">group</span> </pre></div> </div> <p id="index-3">There is also a tactic for identities in commutative additive groups called <code class="docutils literal notranslate"><span class="pre">abel</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">AddCommGroup</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="o">(</span><span class="n">y</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">abel</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">AddCommGroup</span> <span class="n">G</span><span class="o">]</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="n">z</span> <span class="o">:</span> <span class="n">G</span><span class="o">)</span> <span class="o">:</span> <span class="n">z</span> <span class="bp">+</span> <span class="n">x</span> <span class="bp">+</span> <span class="o">(</span><span class="n">y</span> <span class="bp">-</span> <span class="n">z</span> <span class="bp">-</span> <span class="n">x</span><span class="o">)</span> <span class="bp">=</span> <span class="n">y</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">abel</span> </pre></div> </div> <p>Interestingly, a group morphism is nothing more than a monoid morphism between groups. So we can copy and paste one of our earlier examples, replacing <code class="docutils literal notranslate"><span class="pre">Monoid</span></code> with <code class="docutils literal notranslate"><span class="pre">Group</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">H</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">→*</span><span class="w"> </span><span class="n">H</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">f.map_mul</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="n">H</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">[</span><span class="n">Group</span> <span class="n">H</span><span class="o">]</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">G</span><span class="o">)</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">→*</span> <span class="n">H</span><span class="o">)</span> <span class="o">:</span> <span class="n">f</span> <span class="o">(</span><span class="n">x</span> <span class="bp">*</span> <span class="n">y</span><span class="o">)</span> <span class="bp">=</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">*</span> <span class="n">f</span> <span class="n">y</span> <span class="o">:=</span> <span class="n">f.map_mul</span> <span class="n">x</span> <span class="n">y</span> </pre></div> </div> <p>Of course we do get some new properties, such as this one:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">H</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">→*</span><span class="w"> </span><span class="n">H</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="bp">⁻¹</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="bp">⁻¹</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">f.map_inv</span><span class="w"> </span><span class="n">x</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="n">H</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">[</span><span class="n">Group</span> <span class="n">H</span><span class="o">]</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">G</span><span class="o">)</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">→*</span> <span class="n">H</span><span class="o">)</span> <span class="o">:</span> <span class="n">f</span> <span class="o">(</span><span class="n">x</span><span class="bp">⁻¹</span><span class="o">)</span> <span class="bp">=</span> <span class="o">(</span><span class="n">f</span> <span class="n">x</span><span class="o">)</span><span class="bp">⁻¹</span> <span class="o">:=</span> <span class="n">f.map_inv</span> <span class="n">x</span> </pre></div> </div> <p>You may be worried that constructing group morphisms will require us to do unnecessary work since
-
@@ -207,9 +203,9 @@ the definition of monoid morphism enforces that neutral elements are sent to neuwhile this is automatic in the case of group morphisms. In practice the extra work is not hard, but, to avoid it, there is a function building a group morphism from a function between groups that is compatible with the composition laws.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">H</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">H</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">→*</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">MonoidHom.mk'</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">h</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="n">H</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">[</span><span class="n">Group</span> <span class="n">H</span><span class="o">]</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">→</span> <span class="n">H</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span> <span class="n">y</span><span class="o">,</span> <span class="n">f</span> <span class="o">(</span><span class="n">x</span> <span class="bp">*</span> <span class="n">y</span><span class="o">)</span> <span class="bp">=</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">*</span> <span class="n">f</span> <span class="n">y</span><span class="o">)</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">→*</span> <span class="n">H</span> <span class="o">:=</span> <span class="n">MonoidHom.mk'</span> <span class="n">f</span> <span class="n">h</span> </pre></div> </div> <p>There is also a type <code class="docutils literal notranslate"><span class="pre">MulEquiv</span></code> of group (or monoid) isomorphisms denoted by <code class="docutils literal notranslate"><span class="pre">≃*</span></code> (and
-
@@ -220,31 +216,31 @@ the identity isomorphism of <code class="docutils literal notranslate"><span claUsing anonymous projector notation, the first two can be written <code class="docutils literal notranslate"><span class="pre">f.symm</span></code> and <code class="docutils literal notranslate"><span class="pre">f.trans</span> <span class="pre">g</span></code> respectively. Elements of this type are automatically coerced to morphisms and functions when necessary.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">H</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">≃*</span><span class="w"> </span><span class="n">H</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">f.trans</span><span class="w"> </span><span class="n">f.symm</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">MulEquiv.refl</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">f.self_trans_symm</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="n">H</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">[</span><span class="n">Group</span> <span class="n">H</span><span class="o">]</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">≃*</span> <span class="n">H</span><span class="o">)</span> <span class="o">:</span> <span class="n">f.trans</span> <span class="n">f.symm</span> <span class="bp">=</span> <span class="n">MulEquiv.refl</span> <span class="n">G</span> <span class="o">:=</span> <span class="n">f.self_trans_symm</span> </pre></div> </div> <p>One can use <code class="docutils literal notranslate"><span class="pre">MulEquiv.ofBijective</span></code> to build an isomorphism from a bijective morphism. Doing so makes the inverse function noncomputable.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">noncomputable</span><span class="w"> </span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">H</span><span class="o">]</span> <span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">→*</span><span class="w"> </span><span class="n">H</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Function.Bijective</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">≃*</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">MulEquiv.ofBijective</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">h</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">noncomputable</span> <span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="n">H</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">[</span><span class="n">Group</span> <span class="n">H</span><span class="o">]</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">→*</span> <span class="n">H</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">Function.Bijective</span> <span class="n">f</span><span class="o">)</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">≃*</span> <span class="n">H</span> <span class="o">:=</span> <span class="n">MulEquiv.ofBijective</span> <span class="n">f</span> <span class="n">h</span> </pre></div> </div> </section> <section id="subgroups"> <h3><span class="section-number">8.1.3. </span>Subgroups<a class="headerlink" href="#subgroups" title="Link to this heading"></a></h3> <h3><span class="section-number">8.1.3. </span>Subgroups<a class="headerlink" href="#subgroups" title="Permalink to this heading"></a></h3> <p>Just as group morphisms are bundled, a subgroup of <code class="docutils literal notranslate"><span class="pre">G</span></code> is also a bundled structure consisting of a set in <code class="docutils literal notranslate"><span class="pre">G</span></code> with the relevant closure properties.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">H</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hx</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">H</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hy</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">H</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">H.mul_mem</span><span class="w"> </span><span class="n">hx</span><span class="w"> </span><span class="n">hy</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">(</span><span class="n">H</span> <span class="o">:</span> <span class="n">Subgroup</span> <span class="n">G</span><span class="o">)</span> <span class="o">{</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">G</span><span class="o">}</span> <span class="o">(</span><span class="n">hx</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">H</span><span class="o">)</span> <span class="o">(</span><span class="n">hy</span> <span class="o">:</span> <span class="n">y</span> <span class="bp">∈</span> <span class="n">H</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">*</span> <span class="n">y</span> <span class="bp">∈</span> <span class="n">H</span> <span class="o">:=</span> <span class="n">H.mul_mem</span> <span class="n">hx</span> <span class="n">hy</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">H</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hx</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">H</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">x</span><span class="bp">⁻¹</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">H.inv_mem</span><span class="w"> </span><span class="n">hx</span> <span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">(</span><span class="n">H</span> <span class="o">:</span> <span class="n">Subgroup</span> <span class="n">G</span><span class="o">)</span> <span class="o">{</span><span class="n">x</span> <span class="o">:</span> <span class="n">G</span><span class="o">}</span> <span class="o">(</span><span class="n">hx</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">H</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span><span class="bp">⁻¹</span> <span class="bp">∈</span> <span class="n">H</span> <span class="o">:=</span> <span class="n">H.inv_mem</span> <span class="n">hx</span> </pre></div> </div> <p>In the example above, it is important to understand that <code class="docutils literal notranslate"><span class="pre">Subgroup</span> <span class="pre">G</span></code> is the type of subgroups
-
@@ -257,29 +253,29 @@ equal in the same way it is used to prove that two sets are equal.</p><p>To state and prove, for example, that <code class="docutils literal notranslate"><span class="pre">ℤ</span></code> is an additive subgroup of <code class="docutils literal notranslate"><span class="pre">ℚ</span></code>, what we really want is to construct a term of type <code class="docutils literal notranslate"><span class="pre">AddSubgroup</span> <span class="pre">ℚ</span></code> whose projection to <code class="docutils literal notranslate"><span class="pre">Set</span> <span class="pre">ℚ</span></code> is <code class="docutils literal notranslate"><span class="pre">ℤ</span></code>, or, more precisely, the image of <code class="docutils literal notranslate"><span class="pre">ℤ</span></code> in <code class="docutils literal notranslate"><span class="pre">ℚ</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">AddSubgroup</span><span class="w"> </span><span class="n">ℚ</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">carrier</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Set.range</span><span class="w"> </span><span class="o">((</span><span class="bp">↑</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℤ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℚ</span><span class="o">)</span> <span class="w"> </span><span class="n">add_mem'</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rintro</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="o">⟨</span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="n">rfl</span><span class="o">⟩</span><span class="w"> </span><span class="o">⟨</span><span class="n">m</span><span class="o">,</span><span class="w"> </span><span class="n">rfl</span><span class="o">⟩</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">m</span> <span class="w"> </span><span class="n">simp</span> <span class="w"> </span><span class="n">zero_mem'</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="mi">0</span> <span class="w"> </span><span class="n">simp</span> <span class="w"> </span><span class="n">neg_mem'</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rintro</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="o">⟨</span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="n">rfl</span><span class="o">⟩</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="bp">-</span><span class="n">n</span> <span class="w"> </span><span class="n">simp</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">AddSubgroup</span> <span class="n">ℚ</span> <span class="n">where</span> <span class="n">carrier</span> <span class="o">:=</span> <span class="n">Set.range</span> <span class="o">((</span><span class="bp">↑</span><span class="o">)</span> <span class="o">:</span> <span class="n">ℤ</span> <span class="bp">→</span> <span class="n">ℚ</span><span class="o">)</span> <span class="n">add_mem'</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rintro</span> <span class="n">_</span> <span class="n">_</span> <span class="o">⟨</span><span class="n">n</span><span class="o">,</span> <span class="n">rfl</span><span class="o">⟩</span> <span class="o">⟨</span><span class="n">m</span><span class="o">,</span> <span class="n">rfl</span><span class="o">⟩</span> <span class="n">use</span> <span class="n">n</span> <span class="bp">+</span> <span class="n">m</span> <span class="n">simp</span> <span class="n">zero_mem'</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">use</span> <span class="mi">0</span> <span class="n">simp</span> <span class="n">neg_mem'</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rintro</span> <span class="n">_</span> <span class="o">⟨</span><span class="n">n</span><span class="o">,</span> <span class="n">rfl</span><span class="o">⟩</span> <span class="n">use</span> <span class="bp">-</span><span class="n">n</span> <span class="n">simp</span> </pre></div> </div> <p>Using type classes, Mathlib knows that a subgroup of a group inherits a group structure.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">H</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Group</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">inferInstance</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">(</span><span class="n">H</span> <span class="o">:</span> <span class="n">Subgroup</span> <span class="n">G</span><span class="o">)</span> <span class="o">:</span> <span class="n">Group</span> <span class="n">H</span> <span class="o">:=</span> <span class="n">inferInstance</span> </pre></div> </div> <p>This example is subtle. The object <code class="docutils literal notranslate"><span class="pre">H</span></code> is not a type, but Lean automatically coerces it to a type by interpreting it as a subtype of <code class="docutils literal notranslate"><span class="pre">G</span></code>. So the above example can be restated more explicitly as:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">H</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Group</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">//</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">H</span><span class="o">}</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">inferInstance</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">(</span><span class="n">H</span> <span class="o">:</span> <span class="n">Subgroup</span> <span class="n">G</span><span class="o">)</span> <span class="o">:</span> <span class="n">Group</span> <span class="o">{</span><span class="n">x</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">//</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">H</span><span class="o">}</span> <span class="o">:=</span> <span class="n">inferInstance</span> </pre></div> </div> <p>An important benefit of having a type <code class="docutils literal notranslate"><span class="pre">Subgroup</span> <span class="pre">G</span></code> instead of a predicate
-
@@ -291,8 +287,8 @@ have used the lattice operation <code class="docutils literal notranslate"><spanlemmas about lattices to the construction.</p> <p>Let us check that the set underlying the infimum of two subgroups is indeed, by definition, their intersection.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">H</span><span class="w"> </span><span class="n">H'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="o">((</span><span class="n">H</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">H'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">(</span><span class="n">H</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="o">(</span><span class="n">H'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">rfl</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">(</span><span class="n">H</span> <span class="n">H'</span> <span class="o">:</span> <span class="n">Subgroup</span> <span class="n">G</span><span class="o">)</span> <span class="o">:</span> <span class="o">((</span><span class="n">H</span> <span class="bp">⊓</span> <span class="n">H'</span> <span class="o">:</span> <span class="n">Subgroup</span> <span class="n">G</span><span class="o">)</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">G</span><span class="o">)</span> <span class="bp">=</span> <span class="o">(</span><span class="n">H</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">G</span><span class="o">)</span> <span class="bp">∩</span> <span class="o">(</span><span class="n">H'</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">G</span><span class="o">)</span> <span class="o">:=</span> <span class="n">rfl</span> </pre></div> </div> <p>It may look strange to have a different notation for what amounts to the intersection of the
-
@@ -300,36 +296,36 @@ underlying sets, but the correspondence does not carry over to the supremum operunion, since a union of subgroups is not, in general, a subgroup. Instead one needs to use the subgroup generated by the union, which is done using <code class="docutils literal notranslate"><span class="pre">Subgroup.closure</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">H</span><span class="w"> </span><span class="n">H'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="o">((</span><span class="n">H</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">H'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">Subgroup.closure</span><span class="w"> </span><span class="o">((</span><span class="n">H</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="o">(</span><span class="n">H'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">G</span><span class="o">))</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">Subgroup.sup_eq_closure</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">(</span><span class="n">H</span> <span class="n">H'</span> <span class="o">:</span> <span class="n">Subgroup</span> <span class="n">G</span><span class="o">)</span> <span class="o">:</span> <span class="o">((</span><span class="n">H</span> <span class="bp">⊔</span> <span class="n">H'</span> <span class="o">:</span> <span class="n">Subgroup</span> <span class="n">G</span><span class="o">)</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">G</span><span class="o">)</span> <span class="bp">=</span> <span class="n">Subgroup.closure</span> <span class="o">((</span><span class="n">H</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">G</span><span class="o">)</span> <span class="bp">∪</span> <span class="o">(</span><span class="n">H'</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">G</span><span class="o">))</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">Subgroup.sup_eq_closure</span><span class="o">]</span> </pre></div> </div> <p>Another subtlety is that <code class="docutils literal notranslate"><span class="pre">G</span></code> itself does not have type <code class="docutils literal notranslate"><span class="pre">Subgroup</span> <span class="pre">G</span></code>, so we need a way to talk about <code class="docutils literal notranslate"><span class="pre">G</span></code> seen as a subgroup of <code class="docutils literal notranslate"><span class="pre">G</span></code>. This is also provided by the lattice structure: the full subgroup is the top element of this lattice.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="o">(</span><span class="bp">⊤</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">trivial</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">G</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">∈</span> <span class="o">(</span><span class="bp">⊤</span> <span class="o">:</span> <span class="n">Subgroup</span> <span class="n">G</span><span class="o">)</span> <span class="o">:=</span> <span class="n">trivial</span> </pre></div> </div> <p>Similarly the bottom element of this lattice is the subgroup whose only element is the neutral element.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="o">(</span><span class="bp">⊥</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Subgroup.mem_bot</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">G</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">∈</span> <span class="o">(</span><span class="bp">⊥</span> <span class="o">:</span> <span class="n">Subgroup</span> <span class="n">G</span><span class="o">)</span> <span class="bp">↔</span> <span class="n">x</span> <span class="bp">=</span> <span class="mi">1</span> <span class="o">:=</span> <span class="n">Subgroup.mem_bot</span> </pre></div> </div> <p>As an exercise in manipulating groups and subgroups, you can define the conjugate of a subgroup by an element of the ambient group.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">conjugate</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">H</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">carrier</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">h</span><span class="o">,</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">x</span><span class="bp">⁻¹</span><span class="o">}</span> <span class="w"> </span><span class="n">one_mem'</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">dsimp</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">inv_mem'</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">dsimp</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">mul_mem'</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">dsimp</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">conjugate</span> <span class="o">{</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">G</span><span class="o">)</span> <span class="o">(</span><span class="n">H</span> <span class="o">:</span> <span class="n">Subgroup</span> <span class="n">G</span><span class="o">)</span> <span class="o">:</span> <span class="n">Subgroup</span> <span class="n">G</span> <span class="n">where</span> <span class="n">carrier</span> <span class="o">:=</span> <span class="o">{</span><span class="n">a</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">|</span> <span class="bp">∃</span> <span class="n">h</span><span class="o">,</span> <span class="n">h</span> <span class="bp">∈</span> <span class="n">H</span> <span class="bp">∧</span> <span class="n">a</span> <span class="bp">=</span> <span class="n">x</span> <span class="bp">*</span> <span class="n">h</span> <span class="bp">*</span> <span class="n">x</span><span class="bp">⁻¹</span><span class="o">}</span> <span class="n">one_mem'</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">dsimp</span> <span class="gr">sorry</span> <span class="n">inv_mem'</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">dsimp</span> <span class="gr">sorry</span> <span class="n">mul_mem'</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">dsimp</span> <span class="gr">sorry</span> </pre></div> </div> <p>Tying the previous two topics together, one can push forward and pull back subgroups using
-
@@ -337,55 +333,55 @@ group morphisms. The naming convention in Mathlib is to call those operations <cand <code class="docutils literal notranslate"><span class="pre">comap</span></code>. These are not the common mathematical terms, but they have the advantage of being shorter than “pushforward” and “direct image.”</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">H</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">G'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">→*</span><span class="w"> </span><span class="n">H</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Subgroup.map</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">G'</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="n">H</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">[</span><span class="n">Group</span> <span class="n">H</span><span class="o">]</span> <span class="o">(</span><span class="n">G'</span> <span class="o">:</span> <span class="n">Subgroup</span> <span class="n">G</span><span class="o">)</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">→*</span> <span class="n">H</span><span class="o">)</span> <span class="o">:</span> <span class="n">Subgroup</span> <span class="n">H</span> <span class="o">:=</span> <span class="n">Subgroup.map</span> <span class="n">f</span> <span class="n">G'</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">H</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">H'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup</span><span class="w"> </span><span class="n">H</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">→*</span><span class="w"> </span><span class="n">H</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Subgroup.comap</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">H'</span> <span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="n">H</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">[</span><span class="n">Group</span> <span class="n">H</span><span class="o">]</span> <span class="o">(</span><span class="n">H'</span> <span class="o">:</span> <span class="n">Subgroup</span> <span class="n">H</span><span class="o">)</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">→*</span> <span class="n">H</span><span class="o">)</span> <span class="o">:</span> <span class="n">Subgroup</span> <span class="n">G</span> <span class="o">:=</span> <span class="n">Subgroup.comap</span> <span class="n">f</span> <span class="n">H'</span> <span class="k">#check</span><span class="w"> </span><span class="n">Subgroup.mem_map</span> <span class="k">#check</span><span class="w"> </span><span class="n">Subgroup.mem_comap</span> <span class="k">#check</span> <span class="n">Subgroup.mem_map</span> <span class="k">#check</span> <span class="n">Subgroup.mem_comap</span> </pre></div> </div> <p>In particular, the preimage of the bottom subgroup under a morphism <code class="docutils literal notranslate"><span class="pre">f</span></code> is a subgroup called the <em>kernel</em> of <code class="docutils literal notranslate"><span class="pre">f</span></code>, and the range of <code class="docutils literal notranslate"><span class="pre">f</span></code> is also a subgroup.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">H</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">→*</span><span class="w"> </span><span class="n">H</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">g</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">MonoidHom.ker</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">f.mem_ker</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="n">H</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">[</span><span class="n">Group</span> <span class="n">H</span><span class="o">]</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">→*</span> <span class="n">H</span><span class="o">)</span> <span class="o">(</span><span class="n">g</span> <span class="o">:</span> <span class="n">G</span><span class="o">)</span> <span class="o">:</span> <span class="n">g</span> <span class="bp">∈</span> <span class="n">MonoidHom.ker</span> <span class="n">f</span> <span class="bp">↔</span> <span class="n">f</span> <span class="n">g</span> <span class="bp">=</span> <span class="mi">1</span> <span class="o">:=</span> <span class="n">f.mem_ker</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">H</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">→*</span><span class="w"> </span><span class="n">H</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">H</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">MonoidHom.range</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">f.mem_range</span> <span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="n">H</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">[</span><span class="n">Group</span> <span class="n">H</span><span class="o">]</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">→*</span> <span class="n">H</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">H</span><span class="o">)</span> <span class="o">:</span> <span class="n">h</span> <span class="bp">∈</span> <span class="n">MonoidHom.range</span> <span class="n">f</span> <span class="bp">↔</span> <span class="bp">∃</span> <span class="n">g</span> <span class="o">:</span> <span class="n">G</span><span class="o">,</span> <span class="n">f</span> <span class="n">g</span> <span class="bp">=</span> <span class="n">h</span> <span class="o">:=</span> <span class="n">f.mem_range</span> </pre></div> </div> <p>As exercises in manipulating group morphisms and subgroups, let us prove some elementary properties. They are already proved in Mathlib, so do not use <code class="docutils literal notranslate"><span class="pre">exact?</span></code> too quickly if you want to benefit from these exercises.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">section</span><span class="w"> </span><span class="n">exercises</span> <span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">H</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">section</span> <span class="n">exercises</span> <span class="kd">variable</span> <span class="o">{</span><span class="n">G</span> <span class="n">H</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">[</span><span class="n">Group</span> <span class="n">H</span><span class="o">]</span> <span class="kn">open</span><span class="w"> </span><span class="n">Subgroup</span> <span class="kn">open</span> <span class="n">Subgroup</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">→*</span><span class="w"> </span><span class="n">H</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">S</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup</span><span class="w"> </span><span class="n">H</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hST</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">T</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">comap</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">comap</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">→*</span> <span class="n">H</span><span class="o">)</span> <span class="o">(</span><span class="n">S</span> <span class="n">T</span> <span class="o">:</span> <span class="n">Subgroup</span> <span class="n">H</span><span class="o">)</span> <span class="o">(</span><span class="n">hST</span> <span class="o">:</span> <span class="n">S</span> <span class="bp">≤</span> <span class="n">T</span><span class="o">)</span> <span class="o">:</span> <span class="n">comap</span> <span class="n">φ</span> <span class="n">S</span> <span class="bp">≤</span> <span class="n">comap</span> <span class="n">φ</span> <span class="n">T</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">→*</span><span class="w"> </span><span class="n">H</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">S</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hST</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">T</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">map</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">map</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">→*</span> <span class="n">H</span><span class="o">)</span> <span class="o">(</span><span class="n">S</span> <span class="n">T</span> <span class="o">:</span> <span class="n">Subgroup</span> <span class="n">G</span><span class="o">)</span> <span class="o">(</span><span class="n">hST</span> <span class="o">:</span> <span class="n">S</span> <span class="bp">≤</span> <span class="n">T</span><span class="o">)</span> <span class="o">:</span> <span class="n">map</span> <span class="n">φ</span> <span class="n">S</span> <span class="bp">≤</span> <span class="n">map</span> <span class="n">φ</span> <span class="n">T</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">K</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">K</span><span class="o">]</span> <span class="kd">variable</span> <span class="o">{</span><span class="n">K</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">K</span><span class="o">]</span> <span class="c1">-- Remember you can use the `ext` tactic to prove an equality of subgroups.</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">→*</span><span class="w"> </span><span class="n">H</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">ψ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="bp">→*</span><span class="w"> </span><span class="n">K</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">U</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup</span><span class="w"> </span><span class="n">K</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">comap</span><span class="w"> </span><span class="o">(</span><span class="n">ψ.comp</span><span class="w"> </span><span class="n">φ</span><span class="o">)</span><span class="w"> </span><span class="n">U</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">comap</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="o">(</span><span class="n">comap</span><span class="w"> </span><span class="n">ψ</span><span class="w"> </span><span class="n">U</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">→*</span> <span class="n">H</span><span class="o">)</span> <span class="o">(</span><span class="n">ψ</span> <span class="o">:</span> <span class="n">H</span> <span class="bp">→*</span> <span class="n">K</span><span class="o">)</span> <span class="o">(</span><span class="n">U</span> <span class="o">:</span> <span class="n">Subgroup</span> <span class="n">K</span><span class="o">)</span> <span class="o">:</span> <span class="n">comap</span> <span class="o">(</span><span class="n">ψ.comp</span> <span class="n">φ</span><span class="o">)</span> <span class="n">U</span> <span class="bp">=</span> <span class="n">comap</span> <span class="n">φ</span> <span class="o">(</span><span class="n">comap</span> <span class="n">ψ</span> <span class="n">U</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="c1">-- Pushing a subgroup along one homomorphism and then another is equal to</span> <span class="c1">-- pushing it forward along the composite of the homomorphisms.</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">→*</span><span class="w"> </span><span class="n">H</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">ψ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="bp">→*</span><span class="w"> </span><span class="n">K</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">S</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">map</span><span class="w"> </span><span class="o">(</span><span class="n">ψ.comp</span><span class="w"> </span><span class="n">φ</span><span class="o">)</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">map</span><span class="w"> </span><span class="n">ψ</span><span class="w"> </span><span class="o">(</span><span class="n">S.map</span><span class="w"> </span><span class="n">φ</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">→*</span> <span class="n">H</span><span class="o">)</span> <span class="o">(</span><span class="n">ψ</span> <span class="o">:</span> <span class="n">H</span> <span class="bp">→*</span> <span class="n">K</span><span class="o">)</span> <span class="o">(</span><span class="n">S</span> <span class="o">:</span> <span class="n">Subgroup</span> <span class="n">G</span><span class="o">)</span> <span class="o">:</span> <span class="n">map</span> <span class="o">(</span><span class="n">ψ.comp</span> <span class="n">φ</span><span class="o">)</span> <span class="n">S</span> <span class="bp">=</span> <span class="n">map</span> <span class="n">ψ</span> <span class="o">(</span><span class="n">S.map</span> <span class="n">φ</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">end</span><span class="w"> </span><span class="n">exercises</span> <span class="kd">end</span> <span class="n">exercises</span> </pre></div> </div> <p>Let us finish this introduction to subgroups in Mathlib with two very classical results.
-
@@ -393,47 +389,47 @@ Lagrange theorem states the cardinality of a subgroup of a finite group dividesthe group. Sylow’s first theorem is a famous partial converse to Lagrange’s theorem.</p> <p>While this corner of Mathlib is partly set up to allow computation, we can tell Lean to use nonconstructive logic anyway using the following <code class="docutils literal notranslate"><span class="pre">open</span> <span class="pre">scoped</span></code> command.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span><span class="w"> </span><span class="n">scoped</span><span class="w"> </span><span class="n">Classical</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span> <span class="n">scoped</span> <span class="n">Classical</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">G'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat.card</span><span class="w"> </span><span class="n">G'</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">Nat.card</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">⟨</span><span class="n">G'.index</span><span class="o">,</span><span class="w"> </span><span class="n">mul_comm</span><span class="w"> </span><span class="n">G'.index</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">▸</span><span class="w"> </span><span class="n">G'.index_mul_card.symm</span><span class="o">⟩</span> <span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">(</span><span class="n">G'</span> <span class="o">:</span> <span class="n">Subgroup</span> <span class="n">G</span><span class="o">)</span> <span class="o">:</span> <span class="n">Nat.card</span> <span class="n">G'</span> <span class="bp">∣</span> <span class="n">Nat.card</span> <span class="n">G</span> <span class="o">:=</span> <span class="o">⟨</span><span class="n">G'.index</span><span class="o">,</span> <span class="n">mul_comm</span> <span class="n">G'.index</span> <span class="n">_</span> <span class="bp">▸</span> <span class="n">G'.index_mul_card.symm</span><span class="o">⟩</span> <span class="kn">open</span><span class="w"> </span><span class="n">Subgroup</span> <span class="kn">open</span> <span class="n">Subgroup</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Finite</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">p</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">{</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Fact</span><span class="w"> </span><span class="n">p.Prime</span><span class="o">]</span> <span class="w"> </span><span class="o">(</span><span class="n">hdvd</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">∣</span><span class="w"> </span><span class="n">Nat.card</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup</span><span class="w"> </span><span class="n">G</span><span class="o">,</span><span class="w"> </span><span class="n">Nat.card</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Sylow.exists_subgroup_card_pow_prime</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="n">hdvd</span> <span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">[</span><span class="n">Finite</span> <span class="n">G</span><span class="o">]</span> <span class="o">(</span><span class="n">p</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">{</span><span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">}</span> <span class="o">[</span><span class="n">Fact</span> <span class="n">p.Prime</span><span class="o">]</span> <span class="o">(</span><span class="n">hdvd</span> <span class="o">:</span> <span class="n">p</span> <span class="bp">^</span> <span class="n">n</span> <span class="bp">∣</span> <span class="n">Nat.card</span> <span class="n">G</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">K</span> <span class="o">:</span> <span class="n">Subgroup</span> <span class="n">G</span><span class="o">,</span> <span class="n">Nat.card</span> <span class="n">K</span> <span class="bp">=</span> <span class="n">p</span> <span class="bp">^</span> <span class="n">n</span> <span class="o">:=</span> <span class="n">Sylow.exists_subgroup_card_pow_prime</span> <span class="n">p</span> <span class="n">hdvd</span> </pre></div> </div> <p>The next two exercises derive a corollary of Lagrange’s lemma. (This is also already in Mathlib, so do not use <code class="docutils literal notranslate"><span class="pre">exact?</span></code> too quickly.)</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">lemma</span><span class="w"> </span><span class="n">eq_bot_iff_card</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">H</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup</span><span class="w"> </span><span class="n">G</span><span class="o">}</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">⊥</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">Nat.card</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="k">suffices</span><span class="w"> </span><span class="o">(</span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">H</span><span class="o">,</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">H</span><span class="o">,</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">H</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">simpa</span><span class="w"> </span><span class="o">[</span><span class="n">eq_bot_iff_forall</span><span class="o">,</span><span class="w"> </span><span class="n">Nat.card_eq_one_iff_exists</span><span class="o">]</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">lemma</span> <span class="n">eq_bot_iff_card</span> <span class="o">{</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">{</span><span class="n">H</span> <span class="o">:</span> <span class="n">Subgroup</span> <span class="n">G</span><span class="o">}</span> <span class="o">:</span> <span class="n">H</span> <span class="bp">=</span> <span class="bp">⊥</span> <span class="bp">↔</span> <span class="n">Nat.card</span> <span class="n">H</span> <span class="bp">=</span> <span class="mi">1</span> <span class="o">:=</span> <span class="kd">by</span> <span class="k">suffices</span> <span class="o">(</span><span class="bp">∀</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">H</span><span class="o">,</span> <span class="n">x</span> <span class="bp">=</span> <span class="mi">1</span><span class="o">)</span> <span class="bp">↔</span> <span class="bp">∃</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">H</span><span class="o">,</span> <span class="bp">∀</span> <span class="n">a</span> <span class="bp">∈</span> <span class="n">H</span><span class="o">,</span> <span class="n">a</span> <span class="bp">=</span> <span class="n">x</span> <span class="kd">by</span> <span class="n">simpa</span> <span class="o">[</span><span class="n">eq_bot_iff_forall</span><span class="o">,</span> <span class="n">Nat.card_eq_one_iff_exists</span><span class="o">]</span> <span class="gr">sorry</span> <span class="k">#check</span><span class="w"> </span><span class="n">card_dvd_of_le</span> <span class="k">#check</span> <span class="n">card_dvd_of_le</span> <span class="kd">lemma</span><span class="w"> </span><span class="n">inf_bot_of_coprime</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">H</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup</span><span class="w"> </span><span class="n">G</span><span class="o">)</span> <span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">Nat.card</span><span class="w"> </span><span class="n">H</span><span class="o">)</span><span class="bp">.</span><span class="n">Coprime</span><span class="w"> </span><span class="o">(</span><span class="n">Nat.card</span><span class="w"> </span><span class="n">K</span><span class="o">))</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">⊥</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">lemma</span> <span class="n">inf_bot_of_coprime</span> <span class="o">{</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">(</span><span class="n">H</span> <span class="n">K</span> <span class="o">:</span> <span class="n">Subgroup</span> <span class="n">G</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="o">(</span><span class="n">Nat.card</span> <span class="n">H</span><span class="o">)</span><span class="bp">.</span><span class="n">Coprime</span> <span class="o">(</span><span class="n">Nat.card</span> <span class="n">K</span><span class="o">))</span> <span class="o">:</span> <span class="n">H</span> <span class="bp">⊓</span> <span class="n">K</span> <span class="bp">=</span> <span class="bp">⊥</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> </section> <section id="concrete-groups"> <h3><span class="section-number">8.1.4. </span>Concrete groups<a class="headerlink" href="#concrete-groups" title="Link to this heading"></a></h3> <h3><span class="section-number">8.1.4. </span>Concrete groups<a class="headerlink" href="#concrete-groups" title="Permalink to this heading"></a></h3> <p>One can also manipulate concrete groups in Mathlib, although this is typically more complicated than working with the abstract theory. For instance, given any type <code class="docutils literal notranslate"><span class="pre">X</span></code>, the group of permutations of <code class="docutils literal notranslate"><span class="pre">X</span></code> is <code class="docutils literal notranslate"><span class="pre">Equiv.Perm</span> <span class="pre">X</span></code>. In particular the symmetric group <span class="math notranslate nohighlight">\(\mathfrak{S}_n\)</span> is <code class="docutils literal notranslate"><span class="pre">Equiv.Perm</span> <span class="pre">(Fin</span> <span class="pre">n)</span></code>. One can state abstract results about this group, for instance saying that <code class="docutils literal notranslate"><span class="pre">Equiv.Perm</span> <span class="pre">X</span></code> is generated by cycles if <code class="docutils literal notranslate"><span class="pre">X</span></code> is finite.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span><span class="w"> </span><span class="n">Equiv</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span> <span class="n">Equiv</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">X</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Finite</span><span class="w"> </span><span class="n">X</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup.closure</span><span class="w"> </span><span class="o">{</span><span class="n">σ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Perm</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">Perm.IsCycle</span><span class="w"> </span><span class="n">σ</span><span class="o">}</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">⊤</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Perm.closure_isCycle</span> <span class="kd">example</span> <span class="o">{</span><span class="n">X</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Finite</span> <span class="n">X</span><span class="o">]</span> <span class="o">:</span> <span class="n">Subgroup.closure</span> <span class="o">{</span><span class="n">σ</span> <span class="o">:</span> <span class="n">Perm</span> <span class="n">X</span> <span class="bp">|</span> <span class="n">Perm.IsCycle</span> <span class="n">σ</span><span class="o">}</span> <span class="bp">=</span> <span class="bp">⊤</span> <span class="o">:=</span> <span class="n">Perm.closure_isCycle</span> </pre></div> </div> <p>One can be fully concrete and compute actual products of cycles. Below we use the <code class="docutils literal notranslate"><span class="pre">#simp</span></code> command,
-
@@ -441,20 +437,20 @@ which calls the <code class="docutils literal notranslate"><span class="pre">simcyclic permutation. In the example, the result is a permutation of <code class="docutils literal notranslate"><span class="pre">ℕ</span></code>. One could use a type ascription such as <code class="docutils literal notranslate"><span class="pre">(1</span> <span class="pre">:</span> <span class="pre">Fin</span> <span class="pre">5)</span></code> on the first number appearing to make it a computation in <code class="docutils literal notranslate"><span class="pre">Perm</span> <span class="pre">(Fin</span> <span class="pre">5)</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="bp">#</span><span class="n">simp</span><span class="w"> </span><span class="o">[</span><span class="n">mul_assoc</span><span class="o">]</span><span class="w"> </span><span class="n">c</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="mi">2</span><span class="o">,</span><span class="w"> </span><span class="mi">3</span><span class="o">]</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">c</span><span class="o">[</span><span class="mi">2</span><span class="o">,</span><span class="w"> </span><span class="mi">3</span><span class="o">,</span><span class="w"> </span><span class="mi">4</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="bp">#</span><span class="n">simp</span> <span class="o">[</span><span class="n">mul_assoc</span><span class="o">]</span> <span class="n">c</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span> <span class="mi">2</span><span class="o">,</span> <span class="mi">3</span><span class="o">]</span> <span class="bp">*</span> <span class="n">c</span><span class="o">[</span><span class="mi">2</span><span class="o">,</span> <span class="mi">3</span><span class="o">,</span> <span class="mi">4</span><span class="o">]</span> </pre></div> </div> <p>Another way to work with concrete groups is to use free groups and group presentations. The free group on a type <code class="docutils literal notranslate"><span class="pre">α</span></code> is <code class="docutils literal notranslate"><span class="pre">FreeGroup</span> <span class="pre">α</span></code> and the inclusion map is <code class="docutils literal notranslate"><span class="pre">FreeGroup.of</span> <span class="pre">:</span> <span class="pre">α</span> <span class="pre">→</span> <span class="pre">FreeGroup</span> <span class="pre">α</span></code>. For instance let us define a type <code class="docutils literal notranslate"><span class="pre">S</span></code> with three elements denoted by <code class="docutils literal notranslate"><span class="pre">a</span></code>, <code class="docutils literal notranslate"><span class="pre">b</span></code> and <code class="docutils literal notranslate"><span class="pre">c</span></code>, and the element <code class="docutils literal notranslate"><span class="pre">ab⁻¹</span></code> of the corresponding free group.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">section</span><span class="w"> </span><span class="n">FreeGroup</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">section</span> <span class="n">FreeGroup</span> <span class="kd">inductive</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">c</span> <span class="kd">inductive</span> <span class="n">S</span> <span class="bp">|</span> <span class="n">a</span> <span class="bp">|</span> <span class="n">b</span> <span class="bp">|</span> <span class="n">c</span> <span class="kn">open</span><span class="w"> </span><span class="n">S</span> <span class="kn">open</span> <span class="n">S</span> <span class="kd">def</span><span class="w"> </span><span class="n">myElement</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FreeGroup</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">(</span><span class="bp">.</span><span class="n">of</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="bp">.</span><span class="n">of</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="bp">⁻¹</span> <span class="kd">def</span> <span class="n">myElement</span> <span class="o">:</span> <span class="n">FreeGroup</span> <span class="n">S</span> <span class="o">:=</span> <span class="o">(</span><span class="bp">.</span><span class="n">of</span> <span class="n">a</span><span class="o">)</span> <span class="bp">*</span> <span class="o">(</span><span class="bp">.</span><span class="n">of</span> <span class="n">b</span><span class="o">)</span><span class="bp">⁻¹</span> </pre></div> </div> <p>Note that we gave the expected type of the definition so that Lean knows that <code class="docutils literal notranslate"><span class="pre">.of</span></code> means
-
@@ -462,10 +458,10 @@ by <code class="docutils literal notranslate"><span class="pre">a</span></code>,<p>The universal property of free groups is embodied as the equivalence <code class="docutils literal notranslate"><span class="pre">FreeGroup.lift</span></code>. For example, let us define the group morphism from <code class="docutils literal notranslate"><span class="pre">FreeGroup</span> <span class="pre">S</span></code> to <code class="docutils literal notranslate"><span class="pre">Perm</span> <span class="pre">(Fin</span> <span class="pre">5)</span></code> that sends <code class="docutils literal notranslate"><span class="pre">a</span></code> to <code class="docutils literal notranslate"><span class="pre">c[1,</span> <span class="pre">2,</span> <span class="pre">3]</span></code>, <code class="docutils literal notranslate"><span class="pre">b</span></code> to <code class="docutils literal notranslate"><span class="pre">c[2,</span> <span class="pre">3,</span> <span class="pre">1]</span></code>, and <code class="docutils literal notranslate"><span class="pre">c</span></code> to <code class="docutils literal notranslate"><span class="pre">c[2,</span> <span class="pre">3]</span></code>,</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">myMorphism</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FreeGroup</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="bp">→*</span><span class="w"> </span><span class="n">Perm</span><span class="w"> </span><span class="o">(</span><span class="n">Fin</span><span class="w"> </span><span class="mi">5</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">FreeGroup.lift</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="bp">.</span><span class="n">a</span><span class="w"> </span><span class="bp">=></span><span class="w"> </span><span class="n">c</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="mi">2</span><span class="o">,</span><span class="w"> </span><span class="mi">3</span><span class="o">]</span> <span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="bp">.</span><span class="n">b</span><span class="w"> </span><span class="bp">=></span><span class="w"> </span><span class="n">c</span><span class="o">[</span><span class="mi">2</span><span class="o">,</span><span class="w"> </span><span class="mi">3</span><span class="o">,</span><span class="w"> </span><span class="mi">1</span><span class="o">]</span> <span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="bp">.</span><span class="n">c</span><span class="w"> </span><span class="bp">=></span><span class="w"> </span><span class="n">c</span><span class="o">[</span><span class="mi">2</span><span class="o">,</span><span class="w"> </span><span class="mi">3</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">myMorphism</span> <span class="o">:</span> <span class="n">FreeGroup</span> <span class="n">S</span> <span class="bp">→*</span> <span class="n">Perm</span> <span class="o">(</span><span class="n">Fin</span> <span class="mi">5</span><span class="o">)</span> <span class="o">:=</span> <span class="n">FreeGroup.lift</span> <span class="k">fun</span> <span class="bp">|</span> <span class="bp">.</span><span class="n">a</span> <span class="bp">=></span> <span class="n">c</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span> <span class="mi">2</span><span class="o">,</span> <span class="mi">3</span><span class="o">]</span> <span class="bp">|</span> <span class="bp">.</span><span class="n">b</span> <span class="bp">=></span> <span class="n">c</span><span class="o">[</span><span class="mi">2</span><span class="o">,</span> <span class="mi">3</span><span class="o">,</span> <span class="mi">1</span><span class="o">]</span> <span class="bp">|</span> <span class="bp">.</span><span class="n">c</span> <span class="bp">=></span> <span class="n">c</span><span class="o">[</span><span class="mi">2</span><span class="o">,</span> <span class="mi">3</span><span class="o">]</span> </pre></div> </div> <p>As a last concrete example, let us see how to define a group generated by a single element whose
-
@@ -477,30 +473,30 @@ i.e. a set of elements of some free group, and returns a group that is this freeby a normal subgroup generated by relations. (We will see how to handle more general quotients in <a class="reference internal" href="#quotient-groups"><span class="std std-numref">Section 8.1.6</span></a>.) Since we somehow hide this behind a definition, we use <code class="docutils literal notranslate"><span class="pre">deriving</span> <span class="pre">Group</span></code> to force creation of a group instance on <code class="docutils literal notranslate"><span class="pre">myGroup</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">myGroup</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">PresentedGroup</span><span class="w"> </span><span class="o">{</span><span class="bp">.</span><span class="n">of</span><span class="w"> </span><span class="o">()</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">3</span><span class="o">}</span><span class="w"> </span><span class="n">deriving</span><span class="w"> </span><span class="n">Group</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">myGroup</span> <span class="o">:=</span> <span class="n">PresentedGroup</span> <span class="o">{</span><span class="bp">.</span><span class="n">of</span> <span class="o">()</span> <span class="bp">^</span> <span class="mi">3</span><span class="o">}</span> <span class="n">deriving</span> <span class="n">Group</span> </pre></div> </div> <p>The universal property of presented groups ensures that morphisms out of this group can be built from functions that send the relations to the neutral element of the target group. So we need such a function and a proof that the condition holds. Then we can feed this proof to <code class="docutils literal notranslate"><span class="pre">PresentedGroup.toGroup</span></code> to get the desired group morphism.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">myMap</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Unit</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Perm</span><span class="w"> </span><span class="o">(</span><span class="n">Fin</span><span class="w"> </span><span class="mi">5</span><span class="o">)</span> <span class="bp">|</span><span class="w"> </span><span class="o">()</span><span class="w"> </span><span class="bp">=></span><span class="w"> </span><span class="n">c</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="mi">2</span><span class="o">,</span><span class="w"> </span><span class="mi">3</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">myMap</span> <span class="o">:</span> <span class="n">Unit</span> <span class="bp">→</span> <span class="n">Perm</span> <span class="o">(</span><span class="n">Fin</span> <span class="mi">5</span><span class="o">)</span> <span class="bp">|</span> <span class="o">()</span> <span class="bp">=></span> <span class="n">c</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span> <span class="mi">2</span><span class="o">,</span> <span class="mi">3</span><span class="o">]</span> <span class="kd">lemma</span><span class="w"> </span><span class="n">compat_myMap</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="o">({</span><span class="bp">.</span><span class="n">of</span><span class="w"> </span><span class="o">()</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">3</span><span class="o">}</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="o">(</span><span class="n">FreeGroup</span><span class="w"> </span><span class="n">Unit</span><span class="o">)),</span><span class="w"> </span><span class="n">FreeGroup.lift</span><span class="w"> </span><span class="n">myMap</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rintro</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="n">rfl</span> <span class="w"> </span><span class="n">simp</span> <span class="w"> </span><span class="n">decide</span> <span class="kd">lemma</span> <span class="n">compat_myMap</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">r</span> <span class="bp">∈</span> <span class="o">({</span><span class="bp">.</span><span class="n">of</span> <span class="o">()</span> <span class="bp">^</span> <span class="mi">3</span><span class="o">}</span> <span class="o">:</span> <span class="n">Set</span> <span class="o">(</span><span class="n">FreeGroup</span> <span class="n">Unit</span><span class="o">)),</span> <span class="n">FreeGroup.lift</span> <span class="n">myMap</span> <span class="n">r</span> <span class="bp">=</span> <span class="mi">1</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rintro</span> <span class="n">_</span> <span class="n">rfl</span> <span class="n">simp</span> <span class="n">decide</span> <span class="kd">def</span><span class="w"> </span><span class="n">myNewMorphism</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">myGroup</span><span class="w"> </span><span class="bp">→*</span><span class="w"> </span><span class="n">Perm</span><span class="w"> </span><span class="o">(</span><span class="n">Fin</span><span class="w"> </span><span class="mi">5</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">PresentedGroup.toGroup</span><span class="w"> </span><span class="n">compat_myMap</span> <span class="kd">def</span> <span class="n">myNewMorphism</span> <span class="o">:</span> <span class="n">myGroup</span> <span class="bp">→*</span> <span class="n">Perm</span> <span class="o">(</span><span class="n">Fin</span> <span class="mi">5</span><span class="o">)</span> <span class="o">:=</span> <span class="n">PresentedGroup.toGroup</span> <span class="n">compat_myMap</span> <span class="kd">end</span><span class="w"> </span><span class="n">FreeGroup</span> <span class="kd">end</span> <span class="n">FreeGroup</span> </pre></div> </div> </section> <section id="group-actions"> <h3><span class="section-number">8.1.5. </span>Group actions<a class="headerlink" href="#group-actions" title="Link to this heading"></a></h3> <h3><span class="section-number">8.1.5. </span>Group actions<a class="headerlink" href="#group-actions" title="Permalink to this heading"></a></h3> <p>One important way that group theory interacts with the rest of mathematics is through the use of group actions. An action of a group <code class="docutils literal notranslate"><span class="pre">G</span></code> on some type <code class="docutils literal notranslate"><span class="pre">X</span></code> is nothing more than a morphism from <code class="docutils literal notranslate"><span class="pre">G</span></code> to
-
@@ -512,31 +508,31 @@ requires some contortions, such as defining type synonyms, each of which carriestype class instances.</p> <p>This allows us in particular to use <code class="docutils literal notranslate"><span class="pre">g</span> <span class="pre">•</span> <span class="pre">x</span></code> to denote the action of a group element <code class="docutils literal notranslate"><span class="pre">g</span></code> on a point <code class="docutils literal notranslate"><span class="pre">x</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">noncomputable</span><span class="w"> </span><span class="kn">section</span><span class="w"> </span><span class="n">GroupActions</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">noncomputable</span> <span class="kn">section</span> <span class="n">GroupActions</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">MulAction</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="n">X</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">g</span><span class="w"> </span><span class="n">g'</span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="o">(</span><span class="n">g'</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">(</span><span class="n">g</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">g'</span><span class="o">)</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">(</span><span class="n">mul_smul</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">g'</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="bp">.</span><span class="n">symm</span> <span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="n">X</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">[</span><span class="n">MulAction</span> <span class="n">G</span> <span class="n">X</span><span class="o">]</span> <span class="o">(</span><span class="n">g</span> <span class="n">g'</span><span class="o">:</span> <span class="n">G</span><span class="o">)</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">X</span><span class="o">)</span> <span class="o">:</span> <span class="n">g</span> <span class="bp">•</span> <span class="o">(</span><span class="n">g'</span> <span class="bp">•</span> <span class="n">x</span><span class="o">)</span> <span class="bp">=</span> <span class="o">(</span><span class="n">g</span> <span class="bp">*</span> <span class="n">g'</span><span class="o">)</span> <span class="bp">•</span> <span class="n">x</span> <span class="o">:=</span> <span class="o">(</span><span class="n">mul_smul</span> <span class="n">g</span> <span class="n">g'</span> <span class="n">x</span><span class="o">)</span><span class="bp">.</span><span class="n">symm</span> </pre></div> </div> <p>There is also a version for additive group called <code class="docutils literal notranslate"><span class="pre">AddAction</span></code>, where the action is denoted by <code class="docutils literal notranslate"><span class="pre">+ᵥ</span></code>. This is used for instance in the definition of affine spaces.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">AddGroup</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">AddAction</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="n">X</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">g</span><span class="w"> </span><span class="n">g'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="bp">+ᵥ</span><span class="w"> </span><span class="o">(</span><span class="n">g'</span><span class="w"> </span><span class="bp">+ᵥ</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">(</span><span class="n">g</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">g'</span><span class="o">)</span><span class="w"> </span><span class="bp">+ᵥ</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">(</span><span class="n">add_vadd</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">g'</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="bp">.</span><span class="n">symm</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="n">X</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">AddGroup</span> <span class="n">G</span><span class="o">]</span> <span class="o">[</span><span class="n">AddAction</span> <span class="n">G</span> <span class="n">X</span><span class="o">]</span> <span class="o">(</span><span class="n">g</span> <span class="n">g'</span> <span class="o">:</span> <span class="n">G</span><span class="o">)</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">X</span><span class="o">)</span> <span class="o">:</span> <span class="n">g</span> <span class="bp">+ᵥ</span> <span class="o">(</span><span class="n">g'</span> <span class="bp">+ᵥ</span> <span class="n">x</span><span class="o">)</span> <span class="bp">=</span> <span class="o">(</span><span class="n">g</span> <span class="bp">+</span> <span class="n">g'</span><span class="o">)</span> <span class="bp">+ᵥ</span> <span class="n">x</span> <span class="o">:=</span> <span class="o">(</span><span class="n">add_vadd</span> <span class="n">g</span> <span class="n">g'</span> <span class="n">x</span><span class="o">)</span><span class="bp">.</span><span class="n">symm</span> </pre></div> </div> <p>The underlying group morphism is called <code class="docutils literal notranslate"><span class="pre">MulAction.toPermHom</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span><span class="w"> </span><span class="n">MulAction</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span> <span class="n">MulAction</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">MulAction</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="n">X</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">→*</span><span class="w"> </span><span class="n">Equiv.Perm</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">toPermHom</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="n">X</span> <span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="n">X</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">[</span><span class="n">MulAction</span> <span class="n">G</span> <span class="n">X</span><span class="o">]</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">→*</span> <span class="n">Equiv.Perm</span> <span class="n">X</span> <span class="o">:=</span> <span class="n">toPermHom</span> <span class="n">G</span> <span class="n">X</span> </pre></div> </div> <p>As an illustration let us see how to define the Cayley isomorphism embedding of any group <code class="docutils literal notranslate"><span class="pre">G</span></code> into a permutation group, namely <code class="docutils literal notranslate"><span class="pre">Perm</span> <span class="pre">G</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">CayleyIsoMorphism</span><span class="w"> </span><span class="o">(</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">≃*</span><span class="w"> </span><span class="o">(</span><span class="n">toPermHom</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="bp">.</span><span class="n">range</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Equiv.Perm.subgroupOfMulAction</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="n">G</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">CayleyIsoMorphism</span> <span class="o">(</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">)</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">≃*</span> <span class="o">(</span><span class="n">toPermHom</span> <span class="n">G</span> <span class="n">G</span><span class="o">)</span><span class="bp">.</span><span class="n">range</span> <span class="o">:=</span> <span class="n">Equiv.Perm.subgroupOfMulAction</span> <span class="n">G</span> <span class="n">G</span> </pre></div> </div> <p>Note that nothing before the above definition required having a group rather than a monoid (or any
-
@@ -544,7 +540,7 @@ type endowed with a multiplication operation really).</p><p>The group condition really enters the picture when we will want to partition <code class="docutils literal notranslate"><span class="pre">X</span></code> into orbits. The corresponding equivalence relation on <code class="docutils literal notranslate"><span class="pre">X</span></code> is called <code class="docutils literal notranslate"><span class="pre">MulAction.orbitRel</span></code>. It is not declared as a global instance.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">MulAction</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="n">X</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Setoid</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">orbitRel</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="n">X</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="n">X</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">[</span><span class="n">MulAction</span> <span class="n">G</span> <span class="n">X</span><span class="o">]</span> <span class="o">:</span> <span class="n">Setoid</span> <span class="n">X</span> <span class="o">:=</span> <span class="n">orbitRel</span> <span class="n">G</span> <span class="n">X</span> </pre></div> </div> <p>Using this we can state that <code class="docutils literal notranslate"><span class="pre">X</span></code> is partitioned into orbits under the action of <code class="docutils literal notranslate"><span class="pre">G</span></code>.
-
@@ -553,9 +549,9 @@ More precisely, we get a bijection between <code class="docutils literal notranswhere <code class="docutils literal notranslate"><span class="pre">Quotient.out'</span> <span class="pre">ω</span></code> simply chooses an element that projects to <code class="docutils literal notranslate"><span class="pre">ω</span></code>. Recall that elements of this dependent product are pairs <code class="docutils literal notranslate"><span class="pre">⟨ω,</span> <span class="pre">x⟩</span></code> where the type <code class="docutils literal notranslate"><span class="pre">orbit</span> <span class="pre">G</span> <span class="pre">(Quotient.out'</span> <span class="pre">ω)</span></code> of <code class="docutils literal notranslate"><span class="pre">x</span></code> depends on <code class="docutils literal notranslate"><span class="pre">ω</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">MulAction</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="n">X</span><span class="o">]</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">≃</span><span class="w"> </span><span class="o">(</span><span class="n">ω</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">orbitRel.Quotient</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="n">X</span><span class="o">)</span><span class="w"> </span><span class="bp">×</span><span class="w"> </span><span class="o">(</span><span class="n">orbit</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="o">(</span><span class="n">Quotient.out'</span><span class="w"> </span><span class="n">ω</span><span class="o">))</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">MulAction.selfEquivSigmaOrbits</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="n">X</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="n">X</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">[</span><span class="n">MulAction</span> <span class="n">G</span> <span class="n">X</span><span class="o">]</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">≃</span> <span class="o">(</span><span class="n">ω</span> <span class="o">:</span> <span class="n">orbitRel.Quotient</span> <span class="n">G</span> <span class="n">X</span><span class="o">)</span> <span class="bp">×</span> <span class="o">(</span><span class="n">orbit</span> <span class="n">G</span> <span class="o">(</span><span class="n">Quotient.out'</span> <span class="n">ω</span><span class="o">))</span> <span class="o">:=</span> <span class="n">MulAction.selfEquivSigmaOrbits</span> <span class="n">G</span> <span class="n">X</span> </pre></div> </div> <p>In particular, when X is finite, this can be combined with <code class="docutils literal notranslate"><span class="pre">Fintype.card_congr</span></code> and
-
@@ -565,59 +561,59 @@ Furthermore, the orbits are in bijection with the quotient of <code class="docutstabilizers by left translation. This action of a subgroup by left-translation is used to define quotients of a group by a subgroup with notation <cite>/</cite> so we can use the following concise statement.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">MulAction</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="n">X</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">orbit</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≃</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="n">stabilizer</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">MulAction.orbitEquivQuotientStabilizer</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="n">x</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="n">X</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">[</span><span class="n">MulAction</span> <span class="n">G</span> <span class="n">X</span><span class="o">]</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">X</span><span class="o">)</span> <span class="o">:</span> <span class="n">orbit</span> <span class="n">G</span> <span class="n">x</span> <span class="bp">≃</span> <span class="n">G</span> <span class="bp">⧸</span> <span class="n">stabilizer</span> <span class="n">G</span> <span class="n">x</span> <span class="o">:=</span> <span class="n">MulAction.orbitEquivQuotientStabilizer</span> <span class="n">G</span> <span class="n">x</span> </pre></div> </div> <p>An important special case of combining the above two results is when <code class="docutils literal notranslate"><span class="pre">X</span></code> is a group <code class="docutils literal notranslate"><span class="pre">G</span></code> equipped with the action of a subgroup <code class="docutils literal notranslate"><span class="pre">H</span></code> by translation. In this case all stabilizers are trivial so every orbit is in bijection with <code class="docutils literal notranslate"><span class="pre">H</span></code> and we get:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">H</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">≃</span><span class="w"> </span><span class="o">(</span><span class="n">G</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="n">H</span><span class="o">)</span><span class="w"> </span><span class="bp">×</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">groupEquivQuotientProdSubgroup</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">(</span><span class="n">H</span> <span class="o">:</span> <span class="n">Subgroup</span> <span class="n">G</span><span class="o">)</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">≃</span> <span class="o">(</span><span class="n">G</span> <span class="bp">⧸</span> <span class="n">H</span><span class="o">)</span> <span class="bp">×</span> <span class="n">H</span> <span class="o">:=</span> <span class="n">groupEquivQuotientProdSubgroup</span> </pre></div> </div> <p>This is the conceptual variant of the version of Lagrange theorem that we saw above. Note this version makes no finiteness assumption.</p> <p>As an exercise for this section, let us build the action of a group on its subgroup by conjugation, using our definition of <code class="docutils literal notranslate"><span class="pre">conjugate</span></code> from a previous exercise.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="kd">lemma</span><span class="w"> </span><span class="n">conjugate_one</span><span class="w"> </span><span class="o">(</span><span class="n">H</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">conjugate</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">lemma</span> <span class="n">conjugate_one</span> <span class="o">(</span><span class="n">H</span> <span class="o">:</span> <span class="n">Subgroup</span> <span class="n">G</span><span class="o">)</span> <span class="o">:</span> <span class="n">conjugate</span> <span class="mi">1</span> <span class="n">H</span> <span class="bp">=</span> <span class="n">H</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">instance</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">MulAction</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="o">(</span><span class="n">Subgroup</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">smul</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">conjugate</span> <span class="w"> </span><span class="n">one_smul</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">mul_smul</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">instance</span> <span class="o">:</span> <span class="n">MulAction</span> <span class="n">G</span> <span class="o">(</span><span class="n">Subgroup</span> <span class="n">G</span><span class="o">)</span> <span class="n">where</span> <span class="n">smul</span> <span class="o">:=</span> <span class="n">conjugate</span> <span class="n">one_smul</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="n">mul_smul</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">end</span><span class="w"> </span><span class="n">GroupActions</span> <span class="kd">end</span> <span class="n">GroupActions</span> </pre></div> </div> </section> <section id="quotient-groups"> <span id="id1"></span><h3><span class="section-number">8.1.6. </span>Quotient groups<a class="headerlink" href="#quotient-groups" title="Link to this heading"></a></h3> <span id="id1"></span><h3><span class="section-number">8.1.6. </span>Quotient groups<a class="headerlink" href="#quotient-groups" title="Permalink to this heading"></a></h3> <p>In the above discussion of subgroups acting on groups, we saw the quotient <code class="docutils literal notranslate"><span class="pre">G</span> <span class="pre">⧸</span> <span class="pre">H</span></code> appear. In general this is only a type. It can be endowed with a group structure such that the quotient map is a group morphism if and only if <code class="docutils literal notranslate"><span class="pre">H</span></code> is a normal subgroup (and this group structure is then unique).</p> <p>The normality assumption is a type class <code class="docutils literal notranslate"><span class="pre">Subgroup.Normal</span></code> so that type class inference can use it to derive the group structure on the quotient.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">noncomputable</span><span class="w"> </span><span class="kn">section</span><span class="w"> </span><span class="n">QuotientGroup</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">noncomputable</span> <span class="kn">section</span> <span class="n">QuotientGroup</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">H</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">H.Normal</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Group</span><span class="w"> </span><span class="o">(</span><span class="n">G</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="n">H</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">inferInstance</span> <span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">(</span><span class="n">H</span> <span class="o">:</span> <span class="n">Subgroup</span> <span class="n">G</span><span class="o">)</span> <span class="o">[</span><span class="n">H.Normal</span><span class="o">]</span> <span class="o">:</span> <span class="n">Group</span> <span class="o">(</span><span class="n">G</span> <span class="bp">⧸</span> <span class="n">H</span><span class="o">)</span> <span class="o">:=</span> <span class="n">inferInstance</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">H</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">H.Normal</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">→*</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">QuotientGroup.mk'</span><span class="w"> </span><span class="n">H</span> <span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">(</span><span class="n">H</span> <span class="o">:</span> <span class="n">Subgroup</span> <span class="n">G</span><span class="o">)</span> <span class="o">[</span><span class="n">H.Normal</span><span class="o">]</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">→*</span> <span class="n">G</span> <span class="bp">⧸</span> <span class="n">H</span> <span class="o">:=</span> <span class="n">QuotientGroup.mk'</span> <span class="n">H</span> </pre></div> </div> <p>The universal property of quotient groups is accessed through <code class="docutils literal notranslate"><span class="pre">QuotientGroup.lift</span></code>: a group morphism <code class="docutils literal notranslate"><span class="pre">φ</span></code> descends to <code class="docutils literal notranslate"><span class="pre">G</span> <span class="pre">⧸</span> <span class="pre">N</span></code> as soon as its kernel contains <code class="docutils literal notranslate"><span class="pre">N</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">N</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">N.Normal</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">M</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">→*</span><span class="w"> </span><span class="n">M</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">MonoidHom.ker</span><span class="w"> </span><span class="n">φ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="bp">→*</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">QuotientGroup.lift</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">h</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">(</span><span class="n">N</span> <span class="o">:</span> <span class="n">Subgroup</span> <span class="n">G</span><span class="o">)</span> <span class="o">[</span><span class="n">N.Normal</span><span class="o">]</span> <span class="o">{</span><span class="n">M</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">M</span><span class="o">]</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">→*</span> <span class="n">M</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">N</span> <span class="bp">≤</span> <span class="n">MonoidHom.ker</span> <span class="n">φ</span><span class="o">)</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">⧸</span> <span class="n">N</span> <span class="bp">→*</span> <span class="n">M</span> <span class="o">:=</span> <span class="n">QuotientGroup.lift</span> <span class="n">N</span> <span class="n">φ</span> <span class="n">h</span> </pre></div> </div> <p>The fact that the target group is called <code class="docutils literal notranslate"><span class="pre">M</span></code> is the above snippet is a clue that having a
-
@@ -625,9 +621,9 @@ monoid structure on <code class="docutils literal notranslate"><span class="pre"<p>An important special case is when <code class="docutils literal notranslate"><span class="pre">N</span> <span class="pre">=</span> <span class="pre">ker</span> <span class="pre">φ</span></code>. In that case the descended morphism is injective and we get a group isomorphism onto its image. This result is often called the first isomorphism theorem.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">M</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">→*</span><span class="w"> </span><span class="n">M</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="n">MonoidHom.ker</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="bp">→*</span><span class="w"> </span><span class="n">MonoidHom.range</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">QuotientGroup.quotientKerEquivRange</span><span class="w"> </span><span class="n">φ</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">{</span><span class="n">M</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">M</span><span class="o">]</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">→*</span> <span class="n">M</span><span class="o">)</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">⧸</span> <span class="n">MonoidHom.ker</span> <span class="n">φ</span> <span class="bp">→*</span> <span class="n">MonoidHom.range</span> <span class="n">φ</span> <span class="o">:=</span> <span class="n">QuotientGroup.quotientKerEquivRange</span> <span class="n">φ</span> </pre></div> </div> <p>Applying the universal property to a composition of a morphism <code class="docutils literal notranslate"><span class="pre">φ</span> <span class="pre">:</span> <span class="pre">G</span> <span class="pre">→*</span> <span class="pre">G'</span></code>
-
@@ -637,18 +633,18 @@ The condition required on <code class="docutils literal notranslate"><span class<code class="docutils literal notranslate"><span class="pre">N'</span></code>.” But this is equivalent to asking that <code class="docutils literal notranslate"><span class="pre">φ</span></code> should pull <code class="docutils literal notranslate"><span class="pre">N'</span></code> back over <code class="docutils literal notranslate"><span class="pre">N</span></code>, and the latter condition is nicer to work with since the definition of pullback does not involve an existential quantifier.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="n">G'</span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G'</span><span class="o">]</span> <span class="w"> </span><span class="o">{</span><span class="n">N</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup</span><span class="w"> </span><span class="n">G</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">N.Normal</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">N'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup</span><span class="w"> </span><span class="n">G'</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">N'.Normal</span><span class="o">]</span> <span class="w"> </span><span class="o">{</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">→*</span><span class="w"> </span><span class="n">G'</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">Subgroup.comap</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">N'</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="bp">→*</span><span class="w"> </span><span class="n">G'</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="n">N'</span><span class="o">:=</span> <span class="w"> </span><span class="n">QuotientGroup.map</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="n">N'</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">h</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="n">G'</span><span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G'</span><span class="o">]</span> <span class="o">{</span><span class="n">N</span> <span class="o">:</span> <span class="n">Subgroup</span> <span class="n">G</span><span class="o">}</span> <span class="o">[</span><span class="n">N.Normal</span><span class="o">]</span> <span class="o">{</span><span class="n">N'</span> <span class="o">:</span> <span class="n">Subgroup</span> <span class="n">G'</span><span class="o">}</span> <span class="o">[</span><span class="n">N'.Normal</span><span class="o">]</span> <span class="o">{</span><span class="n">φ</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">→*</span> <span class="n">G'</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">N</span> <span class="bp">≤</span> <span class="n">Subgroup.comap</span> <span class="n">φ</span> <span class="n">N'</span><span class="o">)</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">⧸</span> <span class="n">N</span> <span class="bp">→*</span> <span class="n">G'</span> <span class="bp">⧸</span> <span class="n">N'</span><span class="o">:=</span> <span class="n">QuotientGroup.map</span> <span class="n">N</span> <span class="n">N'</span> <span class="n">φ</span> <span class="n">h</span> </pre></div> </div> <p>One subtle point to keep in mind is that the type <code class="docutils literal notranslate"><span class="pre">G</span> <span class="pre">⧸</span> <span class="pre">N</span></code> really depends on <code class="docutils literal notranslate"><span class="pre">N</span></code> (up to definitional equality), so having a proof that two normal subgroups <code class="docutils literal notranslate"><span class="pre">N</span></code> and <code class="docutils literal notranslate"><span class="pre">M</span></code> are equal is not enough to make the corresponding quotients equal. However the universal properties does give an isomorphism in this case.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">M</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup</span><span class="w"> </span><span class="n">G</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">M.Normal</span><span class="o">]</span> <span class="w"> </span><span class="o">[</span><span class="n">N.Normal</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">N</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="bp">≃*</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">QuotientGroup.quotientMulEquivOfEq</span><span class="w"> </span><span class="n">h</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">{</span><span class="n">M</span> <span class="n">N</span> <span class="o">:</span> <span class="n">Subgroup</span> <span class="n">G</span><span class="o">}</span> <span class="o">[</span><span class="n">M.Normal</span><span class="o">]</span> <span class="o">[</span><span class="n">N.Normal</span><span class="o">]</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">M</span> <span class="bp">=</span> <span class="n">N</span><span class="o">)</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">⧸</span> <span class="n">M</span> <span class="bp">≃*</span> <span class="n">G</span> <span class="bp">⧸</span> <span class="n">N</span> <span class="o">:=</span> <span class="n">QuotientGroup.quotientMulEquivOfEq</span> <span class="n">h</span> </pre></div> </div> <p>As a final series of exercises for this section, we will prove that if <code class="docutils literal notranslate"><span class="pre">H</span></code> and <code class="docutils literal notranslate"><span class="pre">K</span></code> are disjoint
-
@@ -658,58 +654,58 @@ then <code class="docutils literal notranslate"><span class="pre">G</span></code<p>We start with playing a bit with Lagrange’s lemma, without assuming the subgroups are normal or disjoint.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">section</span> <span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Group</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">H</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subgroup</span><span class="w"> </span><span class="n">G</span><span class="o">}</span> <span class="kd">variable</span> <span class="o">{</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Group</span> <span class="n">G</span><span class="o">]</span> <span class="o">{</span><span class="n">H</span> <span class="n">K</span> <span class="o">:</span> <span class="n">Subgroup</span> <span class="n">G</span><span class="o">}</span> <span class="kn">open</span><span class="w"> </span><span class="n">MonoidHom</span> <span class="kn">open</span> <span class="n">MonoidHom</span> <span class="k">#check</span><span class="w"> </span><span class="n">Nat.card_pos</span><span class="w"> </span><span class="c1">-- The nonempty argument will be automatically inferred for subgroups</span> <span class="k">#check</span><span class="w"> </span><span class="n">Subgroup.index_eq_card</span> <span class="k">#check</span><span class="w"> </span><span class="n">Subgroup.index_mul_card</span> <span class="k">#check</span><span class="w"> </span><span class="n">Nat.eq_of_mul_eq_mul_right</span> <span class="k">#check</span> <span class="n">Nat.card_pos</span> <span class="c1">-- The nonempty argument will be automatically inferred for subgroups</span> <span class="k">#check</span> <span class="n">Subgroup.index_eq_card</span> <span class="k">#check</span> <span class="n">Subgroup.index_mul_card</span> <span class="k">#check</span> <span class="n">Nat.eq_of_mul_eq_mul_right</span> <span class="kd">lemma</span><span class="w"> </span><span class="n">aux_card_eq</span><span class="w"> </span><span class="o">[</span><span class="n">Finite</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">h'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat.card</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">Nat.card</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">Nat.card</span><span class="w"> </span><span class="n">K</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">Nat.card</span><span class="w"> </span><span class="o">(</span><span class="n">G</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="n">H</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">Nat.card</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">lemma</span> <span class="n">aux_card_eq</span> <span class="o">[</span><span class="n">Finite</span> <span class="n">G</span><span class="o">]</span> <span class="o">(</span><span class="n">h'</span> <span class="o">:</span> <span class="n">Nat.card</span> <span class="n">G</span> <span class="bp">=</span> <span class="n">Nat.card</span> <span class="n">H</span> <span class="bp">*</span> <span class="n">Nat.card</span> <span class="n">K</span><span class="o">)</span> <span class="o">:</span> <span class="n">Nat.card</span> <span class="o">(</span><span class="n">G</span> <span class="bp">⧸</span> <span class="n">H</span><span class="o">)</span> <span class="bp">=</span> <span class="n">Nat.card</span> <span class="n">K</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>From now on, we assume that our subgroups are normal and disjoint, and we assume the cardinality condition. Now we construct the first building block of the desired isomorphism.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">[</span><span class="n">H.Normal</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">K.Normal</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Fintype</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Disjoint</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="n">K</span><span class="o">)</span> <span class="w"> </span><span class="o">(</span><span class="n">h'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat.card</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">Nat.card</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">Nat.card</span><span class="w"> </span><span class="n">K</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">[</span><span class="n">H.Normal</span><span class="o">]</span> <span class="o">[</span><span class="n">K.Normal</span><span class="o">]</span> <span class="o">[</span><span class="n">Fintype</span> <span class="n">G</span><span class="o">]</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">Disjoint</span> <span class="n">H</span> <span class="n">K</span><span class="o">)</span> <span class="o">(</span><span class="n">h'</span> <span class="o">:</span> <span class="n">Nat.card</span> <span class="n">G</span> <span class="bp">=</span> <span class="n">Nat.card</span> <span class="n">H</span> <span class="bp">*</span> <span class="n">Nat.card</span> <span class="n">K</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="n">Nat.bijective_iff_injective_and_card</span> <span class="k">#check</span><span class="w"> </span><span class="n">ker_eq_bot_iff</span> <span class="k">#check</span><span class="w"> </span><span class="n">restrict</span> <span class="k">#check</span><span class="w"> </span><span class="n">ker_restrict</span> <span class="k">#check</span> <span class="n">Nat.bijective_iff_injective_and_card</span> <span class="k">#check</span> <span class="n">ker_eq_bot_iff</span> <span class="k">#check</span> <span class="n">restrict</span> <span class="k">#check</span> <span class="n">ker_restrict</span> <span class="kd">def</span><span class="w"> </span><span class="n">iso₁</span><span class="w"> </span><span class="o">[</span><span class="n">Fintype</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Disjoint</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="n">K</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nat.card</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">Nat.card</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">Nat.card</span><span class="w"> </span><span class="n">K</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="bp">≃*</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">def</span> <span class="n">iso₁</span> <span class="o">[</span><span class="n">Fintype</span> <span class="n">G</span><span class="o">]</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">Disjoint</span> <span class="n">H</span> <span class="n">K</span><span class="o">)</span> <span class="o">(</span><span class="n">h'</span> <span class="o">:</span> <span class="n">Nat.card</span> <span class="n">G</span> <span class="bp">=</span> <span class="n">Nat.card</span> <span class="n">H</span> <span class="bp">*</span> <span class="n">Nat.card</span> <span class="n">K</span><span class="o">)</span> <span class="o">:</span> <span class="n">K</span> <span class="bp">≃*</span> <span class="n">G</span> <span class="bp">⧸</span> <span class="n">H</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>Now we can define our second building block. We will need <code class="docutils literal notranslate"><span class="pre">MonoidHom.prod</span></code>, which builds a morphism from <code class="docutils literal notranslate"><span class="pre">G₀</span></code> to <code class="docutils literal notranslate"><span class="pre">G₁</span> <span class="pre">×</span> <span class="pre">G₂</span></code> out of morphisms from <code class="docutils literal notranslate"><span class="pre">G₀</span></code> to <code class="docutils literal notranslate"><span class="pre">G₁</span></code> and <code class="docutils literal notranslate"><span class="pre">G₂</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">iso₂</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">≃*</span><span class="w"> </span><span class="o">(</span><span class="n">G</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="n">K</span><span class="o">)</span><span class="w"> </span><span class="bp">×</span><span class="w"> </span><span class="o">(</span><span class="n">G</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="n">H</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">iso₂</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">≃*</span> <span class="o">(</span><span class="n">G</span> <span class="bp">⧸</span> <span class="n">K</span><span class="o">)</span> <span class="bp">×</span> <span class="o">(</span><span class="n">G</span> <span class="bp">⧸</span> <span class="n">H</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>We are ready to put all pieces together.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="n">MulEquiv.prodCongr</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="n">MulEquiv.prodCongr</span> <span class="kd">def</span><span class="w"> </span><span class="n">finalIso</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">≃*</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="bp">×</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">def</span> <span class="n">finalIso</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">≃*</span> <span class="n">H</span> <span class="bp">×</span> <span class="n">K</span> <span class="o">:=</span> <span class="gr">sorry</span> </pre></div> </div> </section> </section> <section id="rings"> <span id="id2"></span><h2><span class="section-number">8.2. </span>Rings<a class="headerlink" href="#rings" title="Link to this heading"></a></h2> <span id="id2"></span><h2><span class="section-number">8.2. </span>Rings<a class="headerlink" href="#rings" title="Permalink to this heading"></a></h2> <section id="rings-their-units-morphisms-and-subrings"> <span id="index-4"></span><h3><span class="section-number">8.2.1. </span>Rings, their units, morphisms and subrings<a class="headerlink" href="#rings-their-units-morphisms-and-subrings" title="Link to this heading"></a></h3> <span id="index-4"></span><h3><span class="section-number">8.2.1. </span>Rings, their units, morphisms and subrings<a class="headerlink" href="#rings-their-units-morphisms-and-subrings" title="Permalink to this heading"></a></h3> <p>The type of ring structures on a type <code class="docutils literal notranslate"><span class="pre">R</span></code> is <code class="docutils literal notranslate"><span class="pre">Ring</span> <span class="pre">R</span></code>. The variant where multiplication is assumed to be commutative is <code class="docutils literal notranslate"><span class="pre">CommRing</span> <span class="pre">R</span></code>. We have already seen that the <code class="docutils literal notranslate"><span class="pre">ring</span></code> tactic will prove any equality that follows from the axioms of a commutative ring.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">R</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">CommRing</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">ring</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">R</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">CommRing</span> <span class="n">R</span><span class="o">]</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">x</span> <span class="bp">+</span> <span class="n">y</span><span class="o">)</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">=</span> <span class="n">x</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">+</span> <span class="n">y</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">+</span> <span class="mi">2</span> <span class="bp">*</span> <span class="n">x</span> <span class="bp">*</span> <span class="n">y</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">ring</span> </pre></div> </div> <p>More exotic variants do not require that the addition on <code class="docutils literal notranslate"><span class="pre">R</span></code> forms a group but only an additive
-
@@ -719,7 +715,7 @@ of functions taking values in the natural numbers.Another important example is the type of ideals in a ring, which will be discussed below. The name of the <code class="docutils literal notranslate"><span class="pre">ring</span></code> tactic is doubly misleading, since it assumes commutativity but works in semirings as well. In other words, it applies to any <code class="docutils literal notranslate"><span class="pre">CommSemiring</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">ring</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">x</span> <span class="bp">+</span> <span class="n">y</span><span class="o">)</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">=</span> <span class="n">x</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">+</span> <span class="n">y</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">+</span> <span class="mi">2</span> <span class="bp">*</span> <span class="n">x</span> <span class="bp">*</span> <span class="n">y</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">ring</span> </pre></div> </div> <p>There are also versions of the ring and semiring classes that do not assume the existence of a
-
@@ -736,33 +732,33 @@ This implementation detail is relevant mainly when defining computable functionssituations one can use <code class="docutils literal notranslate"><span class="pre">IsUnit.unit</span> <span class="pre">{x</span> <span class="pre">:</span> <span class="pre">M}</span> <span class="pre">:</span> <span class="pre">IsUnit</span> <span class="pre">x</span> <span class="pre">→</span> <span class="pre">Mˣ</span></code> to build a unit. In the commutative case, one also has <code class="docutils literal notranslate"><span class="pre">Units.mkOfMulEqOne</span> <span class="pre">(x</span> <span class="pre">y</span> <span class="pre">:</span> <span class="pre">M)</span> <span class="pre">:</span> <span class="pre">x</span> <span class="pre">*</span> <span class="pre">y</span> <span class="pre">=</span> <span class="pre">1</span> <span class="pre">→</span> <span class="pre">Mˣ</span></code> which builds <code class="docutils literal notranslate"><span class="pre">x</span></code> seen as unit.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℤ</span><span class="bp">ˣ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">∨</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">-</span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Int.units_eq_one_or</span><span class="w"> </span><span class="n">x</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">ℤ</span><span class="bp">ˣ</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">=</span> <span class="mi">1</span> <span class="bp">∨</span> <span class="n">x</span> <span class="bp">=</span> <span class="bp">-</span><span class="mi">1</span> <span class="o">:=</span> <span class="n">Int.units_eq_one_or</span> <span class="n">x</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">M</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">M</span><span class="bp">ˣ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">M</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">x</span><span class="bp">⁻¹</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Units.mul_inv</span><span class="w"> </span><span class="n">x</span> <span class="kd">example</span> <span class="o">{</span><span class="n">M</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">M</span><span class="o">]</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">M</span><span class="bp">ˣ</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">M</span><span class="o">)</span> <span class="bp">*</span> <span class="n">x</span><span class="bp">⁻¹</span> <span class="bp">=</span> <span class="mi">1</span> <span class="o">:=</span> <span class="n">Units.mul_inv</span> <span class="n">x</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">M</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Monoid</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Group</span><span class="w"> </span><span class="n">M</span><span class="bp">ˣ</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">inferInstance</span> <span class="kd">example</span> <span class="o">{</span><span class="n">M</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Monoid</span> <span class="n">M</span><span class="o">]</span> <span class="o">:</span> <span class="n">Group</span> <span class="n">M</span><span class="bp">ˣ</span> <span class="o">:=</span> <span class="n">inferInstance</span> </pre></div> </div> <p>The type of ring morphisms between two (semi)-rings <code class="docutils literal notranslate"><span class="pre">R</span></code> and <code class="docutils literal notranslate"><span class="pre">S</span></code> is <code class="docutils literal notranslate"><span class="pre">RingHom</span> <span class="pre">R</span> <span class="pre">S</span></code>, with notation <code class="docutils literal notranslate"><span class="pre">R</span> <span class="pre">→+*</span> <span class="pre">S</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">R</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Ring</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Ring</span><span class="w"> </span><span class="n">S</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="bp">→+*</span><span class="w"> </span><span class="n">S</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">f.map_add</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">R</span> <span class="n">S</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Ring</span> <span class="n">R</span><span class="o">]</span> <span class="o">[</span><span class="n">Ring</span> <span class="n">S</span><span class="o">]</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">R</span> <span class="bp">→+*</span> <span class="n">S</span><span class="o">)</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="o">:</span> <span class="n">f</span> <span class="o">(</span><span class="n">x</span> <span class="bp">+</span> <span class="n">y</span><span class="o">)</span> <span class="bp">=</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">f</span> <span class="n">y</span> <span class="o">:=</span> <span class="n">f.map_add</span> <span class="n">x</span> <span class="n">y</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">R</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Ring</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Ring</span><span class="w"> </span><span class="n">S</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="bp">→+*</span><span class="w"> </span><span class="n">S</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="bp">ˣ</span><span class="w"> </span><span class="bp">→*</span><span class="w"> </span><span class="n">S</span><span class="bp">ˣ</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Units.map</span><span class="w"> </span><span class="n">f</span> <span class="kd">example</span> <span class="o">{</span><span class="n">R</span> <span class="n">S</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Ring</span> <span class="n">R</span><span class="o">]</span> <span class="o">[</span><span class="n">Ring</span> <span class="n">S</span><span class="o">]</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">R</span> <span class="bp">→+*</span> <span class="n">S</span><span class="o">)</span> <span class="o">:</span> <span class="n">R</span><span class="bp">ˣ</span> <span class="bp">→*</span> <span class="n">S</span><span class="bp">ˣ</span> <span class="o">:=</span> <span class="n">Units.map</span> <span class="n">f</span> </pre></div> </div> <p>The isomorphism variant is <code class="docutils literal notranslate"><span class="pre">RingEquiv</span></code>, with notation <code class="docutils literal notranslate"><span class="pre">≃+*</span></code>.</p> <p>As with submonoids and subgroups, there is a <code class="docutils literal notranslate"><span class="pre">Subring</span> <span class="pre">R</span></code> type for subrings of a ring <code class="docutils literal notranslate"><span class="pre">R</span></code>, but this type is a lot less useful than the type of subgroups since one cannot quotient a ring by a subring.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">R</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Ring</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">S</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Subring</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Ring</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">inferInstance</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">R</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Ring</span> <span class="n">R</span><span class="o">]</span> <span class="o">(</span><span class="n">S</span> <span class="o">:</span> <span class="n">Subring</span> <span class="n">R</span><span class="o">)</span> <span class="o">:</span> <span class="n">Ring</span> <span class="n">S</span> <span class="o">:=</span> <span class="n">inferInstance</span> </pre></div> </div> <p>Also notice that <code class="docutils literal notranslate"><span class="pre">RingHom.range</span></code> produces a subring.</p> </section> <section id="ideals-and-quotients"> <h3><span class="section-number">8.2.2. </span>Ideals and quotients<a class="headerlink" href="#ideals-and-quotients" title="Link to this heading"></a></h3> <h3><span class="section-number">8.2.2. </span>Ideals and quotients<a class="headerlink" href="#ideals-and-quotients" title="Permalink to this heading"></a></h3> <p>For historical reasons, Mathlib only has a theory of ideals for commutative rings. (The ring library was originally developed to make quick progress toward the foundations of modern algebraic geometry.) So in this section we will work with commutative (semi)rings.
-
@@ -773,40 +769,40 @@ ideals. But anonymous projection notation won’t always work as expected. Fone cannot replace <code class="docutils literal notranslate"><span class="pre">Ideal.Quotient.mk</span> <span class="pre">I</span></code> by <code class="docutils literal notranslate"><span class="pre">I.Quotient.mk</span></code> in the snippet below because there are two <code class="docutils literal notranslate"><span class="pre">.``s</span> <span class="pre">and</span> <span class="pre">so</span> <span class="pre">it</span> <span class="pre">will</span> <span class="pre">parse</span> <span class="pre">as</span> <span class="pre">``(Ideal.Quotient</span> <span class="pre">I).mk</span></code>; but <code class="docutils literal notranslate"><span class="pre">Ideal.Quotient</span></code> by itself doesn’t exist.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">R</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">CommRing</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">I</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Ideal</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="bp">→+*</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Ideal.Quotient.mk</span><span class="w"> </span><span class="n">I</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">R</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">CommRing</span> <span class="n">R</span><span class="o">]</span> <span class="o">(</span><span class="n">I</span> <span class="o">:</span> <span class="n">Ideal</span> <span class="n">R</span><span class="o">)</span> <span class="o">:</span> <span class="n">R</span> <span class="bp">→+*</span> <span class="n">R</span> <span class="bp">⧸</span> <span class="n">I</span> <span class="o">:=</span> <span class="n">Ideal.Quotient.mk</span> <span class="n">I</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">R</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">CommRing</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">I</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Ideal</span><span class="w"> </span><span class="n">R</span><span class="o">}</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">Ideal.Quotient.mk</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Ideal.Quotient.eq_zero_iff_mem</span> <span class="kd">example</span> <span class="o">{</span><span class="n">R</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">CommRing</span> <span class="n">R</span><span class="o">]</span> <span class="o">{</span><span class="n">a</span> <span class="o">:</span> <span class="n">R</span><span class="o">}</span> <span class="o">{</span><span class="n">I</span> <span class="o">:</span> <span class="n">Ideal</span> <span class="n">R</span><span class="o">}</span> <span class="o">:</span> <span class="n">Ideal.Quotient.mk</span> <span class="n">I</span> <span class="n">a</span> <span class="bp">=</span> <span class="mi">0</span> <span class="bp">↔</span> <span class="n">a</span> <span class="bp">∈</span> <span class="n">I</span> <span class="o">:=</span> <span class="n">Ideal.Quotient.eq_zero_iff_mem</span> </pre></div> </div> <p>The universal property of quotient rings is <code class="docutils literal notranslate"><span class="pre">Ideal.Quotient.lift</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">R</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">CommRing</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">CommRing</span><span class="w"> </span><span class="n">S</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">I</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Ideal</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="bp">→+*</span><span class="w"> </span><span class="n">S</span><span class="o">)</span> <span class="w"> </span><span class="o">(</span><span class="n">H</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">RingHom.ker</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="bp">→+*</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Ideal.Quotient.lift</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">H</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">R</span> <span class="n">S</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">CommRing</span> <span class="n">R</span><span class="o">]</span> <span class="o">[</span><span class="n">CommRing</span> <span class="n">S</span><span class="o">]</span> <span class="o">(</span><span class="n">I</span> <span class="o">:</span> <span class="n">Ideal</span> <span class="n">R</span><span class="o">)</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">R</span> <span class="bp">→+*</span> <span class="n">S</span><span class="o">)</span> <span class="o">(</span><span class="n">H</span> <span class="o">:</span> <span class="n">I</span> <span class="bp">≤</span> <span class="n">RingHom.ker</span> <span class="n">f</span><span class="o">)</span> <span class="o">:</span> <span class="n">R</span> <span class="bp">⧸</span> <span class="n">I</span> <span class="bp">→+*</span> <span class="n">S</span> <span class="o">:=</span> <span class="n">Ideal.Quotient.lift</span> <span class="n">I</span> <span class="n">f</span> <span class="n">H</span> </pre></div> </div> <p>In particular it leads to the first isomorphism theorem for rings.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">R</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">CommRing</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">CommRing</span><span class="w"> </span><span class="n">S</span><span class="o">](</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="bp">→+*</span><span class="w"> </span><span class="n">S</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="n">RingHom.ker</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">≃+*</span><span class="w"> </span><span class="n">f.range</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">RingHom.quotientKerEquivRange</span><span class="w"> </span><span class="n">f</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">R</span> <span class="n">S</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">CommRing</span> <span class="n">R</span><span class="o">]</span> <span class="o">[</span><span class="n">CommRing</span> <span class="n">S</span><span class="o">](</span><span class="n">f</span> <span class="o">:</span> <span class="n">R</span> <span class="bp">→+*</span> <span class="n">S</span><span class="o">)</span> <span class="o">:</span> <span class="n">R</span> <span class="bp">⧸</span> <span class="n">RingHom.ker</span> <span class="n">f</span> <span class="bp">≃+*</span> <span class="n">f.range</span> <span class="o">:=</span> <span class="n">RingHom.quotientKerEquivRange</span> <span class="n">f</span> </pre></div> </div> <p>Ideals form a complete lattice structure with the inclusion relation, as well as a semiring structure. These two structures interact nicely.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">R</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">CommRing</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">I</span><span class="w"> </span><span class="n">J</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Ideal</span><span class="w"> </span><span class="n">R</span><span class="o">}</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">R</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">CommRing</span> <span class="n">R</span><span class="o">]</span> <span class="o">{</span><span class="n">I</span> <span class="n">J</span> <span class="o">:</span> <span class="n">Ideal</span> <span class="n">R</span><span class="o">}</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">J</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">J</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">rfl</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">I</span> <span class="bp">+</span> <span class="n">J</span> <span class="bp">=</span> <span class="n">I</span> <span class="bp">⊔</span> <span class="n">J</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">}</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">J</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">I</span><span class="o">,</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">J</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="o">[</span><span class="n">Submodule.mem_sup</span><span class="o">]</span> <span class="kd">example</span> <span class="o">{</span><span class="n">x</span> <span class="o">:</span> <span class="n">R</span><span class="o">}</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">I</span> <span class="bp">+</span> <span class="n">J</span> <span class="bp">↔</span> <span class="bp">∃</span> <span class="n">a</span> <span class="bp">∈</span> <span class="n">I</span><span class="o">,</span> <span class="bp">∃</span> <span class="n">b</span> <span class="bp">∈</span> <span class="n">J</span><span class="o">,</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">x</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> <span class="o">[</span><span class="n">Submodule.mem_sup</span><span class="o">]</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">J</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">J</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Ideal.mul_le_left</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">I</span> <span class="bp">*</span> <span class="n">J</span> <span class="bp">≤</span> <span class="n">J</span> <span class="o">:=</span> <span class="n">Ideal.mul_le_left</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">J</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Ideal.mul_le_right</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">I</span> <span class="bp">*</span> <span class="n">J</span> <span class="bp">≤</span> <span class="n">I</span> <span class="o">:=</span> <span class="n">Ideal.mul_le_right</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">J</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">J</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Ideal.mul_le_inf</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">I</span> <span class="bp">*</span> <span class="n">J</span> <span class="bp">≤</span> <span class="n">I</span> <span class="bp">⊓</span> <span class="n">J</span> <span class="o">:=</span> <span class="n">Ideal.mul_le_inf</span> </pre></div> </div> <p>One can use ring morphisms to push ideals forward and pull them back using <code class="docutils literal notranslate"><span class="pre">Ideal.map</span></code> and
-
@@ -814,128 +810,128 @@ structure. These two structures interact nicely.</p>the latter is more convenient to use since it does not involve an existential quantifier. This explains why it is used to state the condition that allows us to build morphisms between quotient rings.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">R</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">CommRing</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">CommRing</span><span class="w"> </span><span class="n">S</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">I</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Ideal</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">J</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Ideal</span><span class="w"> </span><span class="n">S</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="bp">→+*</span><span class="w"> </span><span class="n">S</span><span class="o">)</span> <span class="w"> </span><span class="o">(</span><span class="n">H</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">Ideal.comap</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">J</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="bp">→+*</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="n">J</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Ideal.quotientMap</span><span class="w"> </span><span class="n">J</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">H</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">R</span> <span class="n">S</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">CommRing</span> <span class="n">R</span><span class="o">]</span> <span class="o">[</span><span class="n">CommRing</span> <span class="n">S</span><span class="o">]</span> <span class="o">(</span><span class="n">I</span> <span class="o">:</span> <span class="n">Ideal</span> <span class="n">R</span><span class="o">)</span> <span class="o">(</span><span class="n">J</span> <span class="o">:</span> <span class="n">Ideal</span> <span class="n">S</span><span class="o">)</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">R</span> <span class="bp">→+*</span> <span class="n">S</span><span class="o">)</span> <span class="o">(</span><span class="n">H</span> <span class="o">:</span> <span class="n">I</span> <span class="bp">≤</span> <span class="n">Ideal.comap</span> <span class="n">f</span> <span class="n">J</span><span class="o">)</span> <span class="o">:</span> <span class="n">R</span> <span class="bp">⧸</span> <span class="n">I</span> <span class="bp">→+*</span> <span class="n">S</span> <span class="bp">⧸</span> <span class="n">J</span> <span class="o">:=</span> <span class="n">Ideal.quotientMap</span> <span class="n">J</span> <span class="n">f</span> <span class="n">H</span> </pre></div> </div> <p>One subtle point is that the type <code class="docutils literal notranslate"><span class="pre">R</span> <span class="pre">⧸</span> <span class="pre">I</span></code> really depends on <code class="docutils literal notranslate"><span class="pre">I</span></code> (up to definitional equality), so having a proof that two ideals <code class="docutils literal notranslate"><span class="pre">I</span></code> and <code class="docutils literal notranslate"><span class="pre">J</span></code> are equal is not enough to make the corresponding quotients equal. However, the universal properties do provide an isomorphism in this case.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">R</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">CommRing</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">I</span><span class="w"> </span><span class="n">J</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Ideal</span><span class="w"> </span><span class="n">R</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">J</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="bp">≃+*</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="n">J</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Ideal.quotEquivOfEq</span><span class="w"> </span><span class="n">h</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">R</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">CommRing</span> <span class="n">R</span><span class="o">]</span> <span class="o">{</span><span class="n">I</span> <span class="n">J</span> <span class="o">:</span> <span class="n">Ideal</span> <span class="n">R</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">I</span> <span class="bp">=</span> <span class="n">J</span><span class="o">)</span> <span class="o">:</span> <span class="n">R</span> <span class="bp">⧸</span> <span class="n">I</span> <span class="bp">≃+*</span> <span class="n">R</span> <span class="bp">⧸</span> <span class="n">J</span> <span class="o">:=</span> <span class="n">Ideal.quotEquivOfEq</span> <span class="n">h</span> </pre></div> </div> <p>We can now present the Chinese remainder isomorphism as an example. Pay attention to the difference between the indexed infimum symbol <code class="docutils literal notranslate"><span class="pre">⨅</span></code> and the big product of types symbol <code class="docutils literal notranslate"><span class="pre">Π</span></code>. Depending on your font, those can be pretty hard to distinguish.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">R</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">CommRing</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">ι</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Fintype</span><span class="w"> </span><span class="n">ι</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Ideal</span><span class="w"> </span><span class="n">R</span><span class="o">)</span> <span class="w"> </span><span class="o">(</span><span class="n">hf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="n">j</span><span class="o">,</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="n">j</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">IsCoprime</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">j</span><span class="o">))</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">R</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="bp">⨅</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="bp">≃+*</span><span class="w"> </span><span class="bp">Π</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Ideal.quotientInfRingEquivPiQuotient</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">hf</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">R</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">CommRing</span> <span class="n">R</span><span class="o">]</span> <span class="o">{</span><span class="n">ι</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Fintype</span> <span class="n">ι</span><span class="o">]</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">ι</span> <span class="bp">→</span> <span class="n">Ideal</span> <span class="n">R</span><span class="o">)</span> <span class="o">(</span><span class="n">hf</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">i</span> <span class="n">j</span><span class="o">,</span> <span class="n">i</span> <span class="bp">≠</span> <span class="n">j</span> <span class="bp">→</span> <span class="n">IsCoprime</span> <span class="o">(</span><span class="n">f</span> <span class="n">i</span><span class="o">)</span> <span class="o">(</span><span class="n">f</span> <span class="n">j</span><span class="o">))</span> <span class="o">:</span> <span class="o">(</span><span class="n">R</span> <span class="bp">⧸</span> <span class="bp">⨅</span> <span class="n">i</span><span class="o">,</span> <span class="n">f</span> <span class="n">i</span><span class="o">)</span> <span class="bp">≃+*</span> <span class="bp">Π</span> <span class="n">i</span><span class="o">,</span> <span class="n">R</span> <span class="bp">⧸</span> <span class="n">f</span> <span class="n">i</span> <span class="o">:=</span> <span class="n">Ideal.quotientInfRingEquivPiQuotient</span> <span class="n">f</span> <span class="n">hf</span> </pre></div> </div> <p>The elementary version of the Chinese remainder theorem, a statement about <code class="docutils literal notranslate"><span class="pre">ZMod</span></code>, can be easily deduced from the previous one:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span><span class="w"> </span><span class="n">BigOperators</span><span class="w"> </span><span class="n">PiNotation</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span> <span class="n">BigOperators</span> <span class="n">PiNotation</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">ι</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Fintype</span><span class="w"> </span><span class="n">ι</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">coprime</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="n">j</span><span class="o">,</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="n">j</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="bp">.</span><span class="n">Coprime</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">j</span><span class="o">))</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">ZMod</span><span class="w"> </span><span class="o">(</span><span class="bp">∏</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="bp">≃+*</span><span class="w"> </span><span class="bp">Π</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">ZMod</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">ZMod.prodEquivPi</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">coprime</span> <span class="kd">example</span> <span class="o">{</span><span class="n">ι</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Fintype</span> <span class="n">ι</span><span class="o">]</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">ι</span> <span class="bp">→</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">(</span><span class="n">coprime</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">i</span> <span class="n">j</span><span class="o">,</span> <span class="n">i</span> <span class="bp">≠</span> <span class="n">j</span> <span class="bp">→</span> <span class="o">(</span><span class="n">a</span> <span class="n">i</span><span class="o">)</span><span class="bp">.</span><span class="n">Coprime</span> <span class="o">(</span><span class="n">a</span> <span class="n">j</span><span class="o">))</span> <span class="o">:</span> <span class="n">ZMod</span> <span class="o">(</span><span class="bp">∏</span> <span class="n">i</span><span class="o">,</span> <span class="n">a</span> <span class="n">i</span><span class="o">)</span> <span class="bp">≃+*</span> <span class="bp">Π</span> <span class="n">i</span><span class="o">,</span> <span class="n">ZMod</span> <span class="o">(</span><span class="n">a</span> <span class="n">i</span><span class="o">)</span> <span class="o">:=</span> <span class="n">ZMod.prodEquivPi</span> <span class="n">a</span> <span class="n">coprime</span> </pre></div> </div> <p>As a series of exercises, we will reprove the Chinese remainder theorem in the general case.</p> <p>We first need to define the map appearing in the theorem, as a ring morphism, using the universal property of quotient rings.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">ι</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">CommRing</span><span class="w"> </span><span class="n">R</span><span class="o">]</span> <span class="kn">open</span><span class="w"> </span><span class="n">Ideal</span><span class="w"> </span><span class="n">Quotient</span><span class="w"> </span><span class="n">Function</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">ι</span> <span class="n">R</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">CommRing</span> <span class="n">R</span><span class="o">]</span> <span class="kn">open</span> <span class="n">Ideal</span> <span class="n">Quotient</span> <span class="n">Function</span> <span class="k">#check</span><span class="w"> </span><span class="k">Pi</span><span class="bp">.</span><span class="n">ringHom</span> <span class="k">#check</span><span class="w"> </span><span class="n">ker_Pi_Quotient_mk</span> <span class="k">#check</span> <span class="k">Pi</span><span class="bp">.</span><span class="n">ringHom</span> <span class="k">#check</span> <span class="n">ker_Pi_Quotient_mk</span> <span class="sd">/-- The homomorphism from ``R ⧸ ⨅ i, I i`` to ``Π i, R ⧸ I i`` featured in the Chinese</span> <span class="sd"> Remainder Theorem. -/</span> <span class="kd">def</span><span class="w"> </span><span class="n">chineseMap</span><span class="w"> </span><span class="o">(</span><span class="n">I</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Ideal</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">R</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="bp">⨅</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="bp">→+*</span><span class="w"> </span><span class="bp">Π</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">def</span> <span class="n">chineseMap</span> <span class="o">(</span><span class="n">I</span> <span class="o">:</span> <span class="n">ι</span> <span class="bp">→</span> <span class="n">Ideal</span> <span class="n">R</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">R</span> <span class="bp">⧸</span> <span class="bp">⨅</span> <span class="n">i</span><span class="o">,</span> <span class="n">I</span> <span class="n">i</span><span class="o">)</span> <span class="bp">→+*</span> <span class="bp">Π</span> <span class="n">i</span><span class="o">,</span> <span class="n">R</span> <span class="bp">⧸</span> <span class="n">I</span> <span class="n">i</span> <span class="o">:=</span> <span class="gr">sorry</span> </pre></div> </div> <p>Make sure the following next two lemmas can be proven by <code class="docutils literal notranslate"><span class="pre">rfl</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">lemma</span><span class="w"> </span><span class="n">chineseMap_mk</span><span class="w"> </span><span class="o">(</span><span class="n">I</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Ideal</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">chineseMap</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="o">(</span><span class="n">Quotient.mk</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">Ideal.Quotient.mk</span><span class="w"> </span><span class="o">(</span><span class="n">I</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">lemma</span> <span class="n">chineseMap_mk</span> <span class="o">(</span><span class="n">I</span> <span class="o">:</span> <span class="n">ι</span> <span class="bp">→</span> <span class="n">Ideal</span> <span class="n">R</span><span class="o">)</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="o">:</span> <span class="n">chineseMap</span> <span class="n">I</span> <span class="o">(</span><span class="n">Quotient.mk</span> <span class="n">_</span> <span class="n">x</span><span class="o">)</span> <span class="bp">=</span> <span class="k">fun</span> <span class="n">i</span> <span class="o">:</span> <span class="n">ι</span> <span class="bp">↦</span> <span class="n">Ideal.Quotient.mk</span> <span class="o">(</span><span class="n">I</span> <span class="n">i</span><span class="o">)</span> <span class="n">x</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="kd">lemma</span><span class="w"> </span><span class="n">chineseMap_mk'</span><span class="w"> </span><span class="o">(</span><span class="n">I</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Ideal</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">i</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">chineseMap</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="o">(</span><span class="n">mk</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">mk</span><span class="w"> </span><span class="o">(</span><span class="n">I</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">lemma</span> <span class="n">chineseMap_mk'</span> <span class="o">(</span><span class="n">I</span> <span class="o">:</span> <span class="n">ι</span> <span class="bp">→</span> <span class="n">Ideal</span> <span class="n">R</span><span class="o">)</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="o">(</span><span class="n">i</span> <span class="o">:</span> <span class="n">ι</span><span class="o">)</span> <span class="o">:</span> <span class="n">chineseMap</span> <span class="n">I</span> <span class="o">(</span><span class="n">mk</span> <span class="n">_</span> <span class="n">x</span><span class="o">)</span> <span class="n">i</span> <span class="bp">=</span> <span class="n">mk</span> <span class="o">(</span><span class="n">I</span> <span class="n">i</span><span class="o">)</span> <span class="n">x</span> <span class="o">:=</span> <span class="gr">sorry</span> </pre></div> </div> <p>The next lemma proves the easy half of the Chinese remainder theorem, without any assumption on the family of ideals. The proof is less than one line long.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="n">injective_lift_iff</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="n">injective_lift_iff</span> <span class="kd">lemma</span><span class="w"> </span><span class="n">chineseMap_inj</span><span class="w"> </span><span class="o">(</span><span class="n">I</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Ideal</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Injective</span><span class="w"> </span><span class="o">(</span><span class="n">chineseMap</span><span class="w"> </span><span class="n">I</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">lemma</span> <span class="n">chineseMap_inj</span> <span class="o">(</span><span class="n">I</span> <span class="o">:</span> <span class="n">ι</span> <span class="bp">→</span> <span class="n">Ideal</span> <span class="n">R</span><span class="o">)</span> <span class="o">:</span> <span class="n">Injective</span> <span class="o">(</span><span class="n">chineseMap</span> <span class="n">I</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>We are now ready for the heart of the theorem, which will show the surjectivity of our <code class="docutils literal notranslate"><span class="pre">chineseMap</span></code>. First we need to know the different ways one can express the coprimality (also called co-maximality assumption). Only the first two will be needed below.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="n">IsCoprime</span> <span class="k">#check</span><span class="w"> </span><span class="n">isCoprime_iff_add</span> <span class="k">#check</span><span class="w"> </span><span class="n">isCoprime_iff_exists</span> <span class="k">#check</span><span class="w"> </span><span class="n">isCoprime_iff_sup_eq</span> <span class="k">#check</span><span class="w"> </span><span class="n">isCoprime_iff_codisjoint</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="n">IsCoprime</span> <span class="k">#check</span> <span class="n">isCoprime_iff_add</span> <span class="k">#check</span> <span class="n">isCoprime_iff_exists</span> <span class="k">#check</span> <span class="n">isCoprime_iff_sup_eq</span> <span class="k">#check</span> <span class="n">isCoprime_iff_codisjoint</span> </pre></div> </div> <p>We take the opportunity to use induction on <code class="docutils literal notranslate"><span class="pre">Finset</span></code>. Relevant lemmas on <code class="docutils literal notranslate"><span class="pre">Finset</span></code> are given below. Remember that the <code class="docutils literal notranslate"><span class="pre">ring</span></code> tactic works for semirings and that the ideals of a ring form a semiring.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="n">Finset.mem_insert_of_mem</span> <span class="k">#check</span><span class="w"> </span><span class="n">Finset.mem_insert_self</span> <span class="kd">theorem</span><span class="w"> </span><span class="n">isCoprime_Inf</span><span class="w"> </span><span class="o">{</span><span class="n">I</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Ideal</span><span class="w"> </span><span class="n">R</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">J</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Ideal</span><span class="w"> </span><span class="n">R</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Finset</span><span class="w"> </span><span class="n">ι</span><span class="o">}</span> <span class="w"> </span><span class="o">(</span><span class="n">hf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">j</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="n">IsCoprime</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="o">(</span><span class="n">J</span><span class="w"> </span><span class="n">j</span><span class="o">))</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">IsCoprime</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="o">(</span><span class="bp">⨅</span><span class="w"> </span><span class="n">j</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="n">J</span><span class="w"> </span><span class="n">j</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">classical</span> <span class="w"> </span><span class="n">simp_rw</span><span class="w"> </span><span class="o">[</span><span class="n">isCoprime_iff_add</span><span class="o">]</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="bp">*</span> <span class="w"> </span><span class="n">induction</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="n">using</span><span class="w"> </span><span class="n">Finset.induction</span><span class="w"> </span><span class="k">with</span> <span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">empty</span><span class="w"> </span><span class="bp">=></span> <span class="w"> </span><span class="n">simp</span> <span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="bp">@</span><span class="n">insert</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="n">hs</span><span class="w"> </span><span class="bp">=></span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">Finset.iInf_insert</span><span class="o">,</span><span class="w"> </span><span class="n">inf_comm</span><span class="o">,</span><span class="w"> </span><span class="n">one_eq_top</span><span class="o">,</span><span class="w"> </span><span class="n">eq_top_iff</span><span class="o">,</span><span class="w"> </span><span class="bp">←</span><span class="w"> </span><span class="n">one_eq_top</span><span class="o">]</span> <span class="w"> </span><span class="n">set</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="bp">⨅</span><span class="w"> </span><span class="n">j</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="n">J</span><span class="w"> </span><span class="n">j</span> <span class="w"> </span><span class="k">calc</span> <span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">I</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">J</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">(</span><span class="mi">1</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">K</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">J</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">J</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="n">Finset.mem_insert_of_mem</span> <span class="k">#check</span> <span class="n">Finset.mem_insert_self</span> <span class="kd">theorem</span> <span class="n">isCoprime_Inf</span> <span class="o">{</span><span class="n">I</span> <span class="o">:</span> <span class="n">Ideal</span> <span class="n">R</span><span class="o">}</span> <span class="o">{</span><span class="n">J</span> <span class="o">:</span> <span class="n">ι</span> <span class="bp">→</span> <span class="n">Ideal</span> <span class="n">R</span><span class="o">}</span> <span class="o">{</span><span class="n">s</span> <span class="o">:</span> <span class="n">Finset</span> <span class="n">ι</span><span class="o">}</span> <span class="o">(</span><span class="n">hf</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">j</span> <span class="bp">∈</span> <span class="n">s</span><span class="o">,</span> <span class="n">IsCoprime</span> <span class="n">I</span> <span class="o">(</span><span class="n">J</span> <span class="n">j</span><span class="o">))</span> <span class="o">:</span> <span class="n">IsCoprime</span> <span class="n">I</span> <span class="o">(</span><span class="bp">⨅</span> <span class="n">j</span> <span class="bp">∈</span> <span class="n">s</span><span class="o">,</span> <span class="n">J</span> <span class="n">j</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">classical</span> <span class="n">simp_rw</span> <span class="o">[</span><span class="n">isCoprime_iff_add</span><span class="o">]</span> <span class="n">at</span> <span class="bp">*</span> <span class="n">induction</span> <span class="n">s</span> <span class="n">using</span> <span class="n">Finset.induction</span> <span class="k">with</span> <span class="bp">|</span> <span class="n">empty</span> <span class="bp">=></span> <span class="n">simp</span> <span class="bp">|</span> <span class="bp">@</span><span class="n">insert</span> <span class="n">i</span> <span class="n">s</span> <span class="n">_</span> <span class="n">hs</span> <span class="bp">=></span> <span class="n">rw</span> <span class="o">[</span><span class="n">Finset.iInf_insert</span><span class="o">,</span> <span class="n">inf_comm</span><span class="o">,</span> <span class="n">one_eq_top</span><span class="o">,</span> <span class="n">eq_top_iff</span><span class="o">,</span> <span class="bp">←</span> <span class="n">one_eq_top</span><span class="o">]</span> <span class="n">set</span> <span class="n">K</span> <span class="o">:=</span> <span class="bp">⨅</span> <span class="n">j</span> <span class="bp">∈</span> <span class="n">s</span><span class="o">,</span> <span class="n">J</span> <span class="n">j</span> <span class="k">calc</span> <span class="mi">1</span> <span class="bp">=</span> <span class="n">I</span> <span class="bp">+</span> <span class="n">K</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="n">_</span> <span class="bp">=</span> <span class="n">I</span> <span class="bp">+</span> <span class="n">K</span> <span class="bp">*</span> <span class="o">(</span><span class="n">I</span> <span class="bp">+</span> <span class="n">J</span> <span class="n">i</span><span class="o">)</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="n">_</span> <span class="bp">=</span> <span class="o">(</span><span class="mi">1</span> <span class="bp">+</span> <span class="n">K</span><span class="o">)</span> <span class="bp">*</span> <span class="n">I</span> <span class="bp">+</span> <span class="n">K</span> <span class="bp">*</span> <span class="n">J</span> <span class="n">i</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="n">_</span> <span class="bp">≤</span> <span class="n">I</span> <span class="bp">+</span> <span class="n">K</span> <span class="bp">⊓</span> <span class="n">J</span> <span class="n">i</span> <span class="o">:=</span> <span class="gr">sorry</span> </pre></div> </div> <p>We can now prove surjectivity of the map appearing in the Chinese remainder theorem.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">lemma</span><span class="w"> </span><span class="n">chineseMap_surj</span><span class="w"> </span><span class="o">[</span><span class="n">Fintype</span><span class="w"> </span><span class="n">ι</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">I</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Ideal</span><span class="w"> </span><span class="n">R</span><span class="o">}</span> <span class="w"> </span><span class="o">(</span><span class="n">hI</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="n">j</span><span class="o">,</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="n">j</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">IsCoprime</span><span class="w"> </span><span class="o">(</span><span class="n">I</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">I</span><span class="w"> </span><span class="n">j</span><span class="o">))</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Surjective</span><span class="w"> </span><span class="o">(</span><span class="n">chineseMap</span><span class="w"> </span><span class="n">I</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">classical</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">g</span> <span class="w"> </span><span class="n">choose</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">hf</span><span class="w"> </span><span class="n">using</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">Ideal.Quotient.mk_surjective</span><span class="w"> </span><span class="o">(</span><span class="n">g</span><span class="w"> </span><span class="n">i</span><span class="o">)</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">key</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">e</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">,</span><span class="w"> </span><span class="n">mk</span><span class="w"> </span><span class="o">(</span><span class="n">I</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="n">e</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">j</span><span class="o">,</span><span class="w"> </span><span class="n">j</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">mk</span><span class="w"> </span><span class="o">(</span><span class="n">I</span><span class="w"> </span><span class="n">j</span><span class="o">)</span><span class="w"> </span><span class="n">e</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">i</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">hI'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">j</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="o">({</span><span class="n">i</span><span class="o">}</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Finset</span><span class="w"> </span><span class="n">ι</span><span class="o">)</span><span class="bp">ᶜ</span><span class="o">,</span><span class="w"> </span><span class="n">IsCoprime</span><span class="w"> </span><span class="o">(</span><span class="n">I</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">I</span><span class="w"> </span><span class="n">j</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">choose</span><span class="w"> </span><span class="n">e</span><span class="w"> </span><span class="n">he</span><span class="w"> </span><span class="n">using</span><span class="w"> </span><span class="n">key</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">mk</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="o">(</span><span class="bp">∑</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">e</span><span class="w"> </span><span class="n">i</span><span class="o">)</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">lemma</span> <span class="n">chineseMap_surj</span> <span class="o">[</span><span class="n">Fintype</span> <span class="n">ι</span><span class="o">]</span> <span class="o">{</span><span class="n">I</span> <span class="o">:</span> <span class="n">ι</span> <span class="bp">→</span> <span class="n">Ideal</span> <span class="n">R</span><span class="o">}</span> <span class="o">(</span><span class="n">hI</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">i</span> <span class="n">j</span><span class="o">,</span> <span class="n">i</span> <span class="bp">≠</span> <span class="n">j</span> <span class="bp">→</span> <span class="n">IsCoprime</span> <span class="o">(</span><span class="n">I</span> <span class="n">i</span><span class="o">)</span> <span class="o">(</span><span class="n">I</span> <span class="n">j</span><span class="o">))</span> <span class="o">:</span> <span class="n">Surjective</span> <span class="o">(</span><span class="n">chineseMap</span> <span class="n">I</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">classical</span> <span class="n">intro</span> <span class="n">g</span> <span class="n">choose</span> <span class="n">f</span> <span class="n">hf</span> <span class="n">using</span> <span class="k">fun</span> <span class="n">i</span> <span class="bp">↦</span> <span class="n">Ideal.Quotient.mk_surjective</span> <span class="o">(</span><span class="n">g</span> <span class="n">i</span><span class="o">)</span> <span class="k">have</span> <span class="n">key</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">i</span><span class="o">,</span> <span class="bp">∃</span> <span class="n">e</span> <span class="o">:</span> <span class="n">R</span><span class="o">,</span> <span class="n">mk</span> <span class="o">(</span><span class="n">I</span> <span class="n">i</span><span class="o">)</span> <span class="n">e</span> <span class="bp">=</span> <span class="mi">1</span> <span class="bp">∧</span> <span class="bp">∀</span> <span class="n">j</span><span class="o">,</span> <span class="n">j</span> <span class="bp">≠</span> <span class="n">i</span> <span class="bp">→</span> <span class="n">mk</span> <span class="o">(</span><span class="n">I</span> <span class="n">j</span><span class="o">)</span> <span class="n">e</span> <span class="bp">=</span> <span class="mi">0</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">i</span> <span class="k">have</span> <span class="n">hI'</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">j</span> <span class="bp">∈</span> <span class="o">({</span><span class="n">i</span><span class="o">}</span> <span class="o">:</span> <span class="n">Finset</span> <span class="n">ι</span><span class="o">)</span><span class="bp">ᶜ</span><span class="o">,</span> <span class="n">IsCoprime</span> <span class="o">(</span><span class="n">I</span> <span class="n">i</span><span class="o">)</span> <span class="o">(</span><span class="n">I</span> <span class="n">j</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="gr">sorry</span> <span class="n">choose</span> <span class="n">e</span> <span class="n">he</span> <span class="n">using</span> <span class="n">key</span> <span class="n">use</span> <span class="n">mk</span> <span class="n">_</span> <span class="o">(</span><span class="bp">∑</span> <span class="n">i</span><span class="o">,</span> <span class="n">f</span> <span class="n">i</span> <span class="bp">*</span> <span class="n">e</span> <span class="n">i</span><span class="o">)</span> <span class="gr">sorry</span> </pre></div> </div> <p>Now all the pieces come together in the following:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">noncomputable</span><span class="w"> </span><span class="kd">def</span><span class="w"> </span><span class="n">chineseIso</span><span class="w"> </span><span class="o">[</span><span class="n">Fintype</span><span class="w"> </span><span class="n">ι</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Ideal</span><span class="w"> </span><span class="n">R</span><span class="o">)</span> <span class="w"> </span><span class="o">(</span><span class="n">hf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="n">j</span><span class="o">,</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="n">j</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">IsCoprime</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">j</span><span class="o">))</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">R</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="bp">⨅</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="bp">≃+*</span><span class="w"> </span><span class="bp">Π</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">Equiv.ofBijective</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="o">⟨</span><span class="n">chineseMap_inj</span><span class="w"> </span><span class="n">f</span><span class="o">,</span><span class="w"> </span><span class="n">chineseMap_surj</span><span class="w"> </span><span class="n">hf</span><span class="o">⟩,</span> <span class="w"> </span><span class="n">chineseMap</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">}</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">noncomputable</span> <span class="kd">def</span> <span class="n">chineseIso</span> <span class="o">[</span><span class="n">Fintype</span> <span class="n">ι</span><span class="o">]</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">ι</span> <span class="bp">→</span> <span class="n">Ideal</span> <span class="n">R</span><span class="o">)</span> <span class="o">(</span><span class="n">hf</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">i</span> <span class="n">j</span><span class="o">,</span> <span class="n">i</span> <span class="bp">≠</span> <span class="n">j</span> <span class="bp">→</span> <span class="n">IsCoprime</span> <span class="o">(</span><span class="n">f</span> <span class="n">i</span><span class="o">)</span> <span class="o">(</span><span class="n">f</span> <span class="n">j</span><span class="o">))</span> <span class="o">:</span> <span class="o">(</span><span class="n">R</span> <span class="bp">⧸</span> <span class="bp">⨅</span> <span class="n">i</span><span class="o">,</span> <span class="n">f</span> <span class="n">i</span><span class="o">)</span> <span class="bp">≃+*</span> <span class="bp">Π</span> <span class="n">i</span><span class="o">,</span> <span class="n">R</span> <span class="bp">⧸</span> <span class="n">f</span> <span class="n">i</span> <span class="o">:=</span> <span class="o">{</span> <span class="n">Equiv.ofBijective</span> <span class="n">_</span> <span class="o">⟨</span><span class="n">chineseMap_inj</span> <span class="n">f</span><span class="o">,</span> <span class="n">chineseMap_surj</span> <span class="n">hf</span><span class="o">⟩,</span> <span class="n">chineseMap</span> <span class="n">f</span> <span class="k">with</span> <span class="o">}</span> </pre></div> </div> </section> <section id="algebras-and-polynomials"> <h3><span class="section-number">8.2.3. </span>Algebras and polynomials<a class="headerlink" href="#algebras-and-polynomials" title="Link to this heading"></a></h3> <h3><span class="section-number">8.2.3. </span>Algebras and polynomials<a class="headerlink" href="#algebras-and-polynomials" title="Permalink to this heading"></a></h3> <p>Given a commutative (semi)ring <code class="docutils literal notranslate"><span class="pre">R</span></code>, an <em>algebra over</em> <code class="docutils literal notranslate"><span class="pre">R</span></code> is a semiring <code class="docutils literal notranslate"><span class="pre">A</span></code> equipped with a ring morphism whose image commutes with every element of <code class="docutils literal notranslate"><span class="pre">A</span></code>. This is encoded as a type class <code class="docutils literal notranslate"><span class="pre">Algebra</span> <span class="pre">R</span> <span class="pre">A</span></code>.
-
@@ -947,13 +943,13 @@ Note that this notion of algebra is sometimes called an <em>associative unital aexistence of more general notions of algebra.</p> <p>The fact that <code class="docutils literal notranslate"><span class="pre">algebraMap</span> <span class="pre">R</span> <span class="pre">A</span></code> is ring morphism packages together a lot of properties of scalar multiplication, such as the following:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">R</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">CommRing</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Ring</span><span class="w"> </span><span class="n">A</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Algebra</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="n">A</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">r</span><span class="w"> </span><span class="n">r'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">A</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="o">(</span><span class="n">r</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">r'</span><span class="o">)</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">r'</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">add_smul</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="n">r'</span><span class="w"> </span><span class="n">a</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">R</span> <span class="n">A</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">CommRing</span> <span class="n">R</span><span class="o">]</span> <span class="o">[</span><span class="n">Ring</span> <span class="n">A</span><span class="o">]</span> <span class="o">[</span><span class="n">Algebra</span> <span class="n">R</span> <span class="n">A</span><span class="o">]</span> <span class="o">(</span><span class="n">r</span> <span class="n">r'</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">A</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">r</span> <span class="bp">+</span> <span class="n">r'</span><span class="o">)</span> <span class="bp">•</span> <span class="n">a</span> <span class="bp">=</span> <span class="n">r</span> <span class="bp">•</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">r'</span> <span class="bp">•</span> <span class="n">a</span> <span class="o">:=</span> <span class="n">add_smul</span> <span class="n">r</span> <span class="n">r'</span> <span class="n">a</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">R</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">CommRing</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Ring</span><span class="w"> </span><span class="n">A</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Algebra</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="n">A</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">r</span><span class="w"> </span><span class="n">r'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">A</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="o">(</span><span class="n">r</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">r'</span><span class="o">)</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">r'</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">mul_smul</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="n">r'</span><span class="w"> </span><span class="n">a</span> <span class="kd">example</span> <span class="o">{</span><span class="n">R</span> <span class="n">A</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">CommRing</span> <span class="n">R</span><span class="o">]</span> <span class="o">[</span><span class="n">Ring</span> <span class="n">A</span><span class="o">]</span> <span class="o">[</span><span class="n">Algebra</span> <span class="n">R</span> <span class="n">A</span><span class="o">]</span> <span class="o">(</span><span class="n">r</span> <span class="n">r'</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">A</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">r</span> <span class="bp">*</span> <span class="n">r'</span><span class="o">)</span> <span class="bp">•</span> <span class="n">a</span> <span class="bp">=</span> <span class="n">r</span> <span class="bp">•</span> <span class="n">r'</span> <span class="bp">•</span> <span class="n">a</span> <span class="o">:=</span> <span class="n">mul_smul</span> <span class="n">r</span> <span class="n">r'</span> <span class="n">a</span> </pre></div> </div> <p>The morphisms between two <code class="docutils literal notranslate"><span class="pre">R</span></code>-algebras <code class="docutils literal notranslate"><span class="pre">A</span></code> and <code class="docutils literal notranslate"><span class="pre">B</span></code> are ring morphisms
-
@@ -968,11 +964,11 @@ which can be written as <code class="docutils literal notranslate"><span class="The algebra structure map from <code class="docutils literal notranslate"><span class="pre">R</span></code> to <code class="docutils literal notranslate"><span class="pre">R[X]</span></code> is denoted by <code class="docutils literal notranslate"><span class="pre">C</span></code>, which stands for “constant” since the corresponding polynomial functions are always constant. The indeterminate is denoted by <code class="docutils literal notranslate"><span class="pre">X</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span><span class="w"> </span><span class="n">Polynomial</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span> <span class="n">Polynomial</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">R</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">CommRing</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">[</span><span class="n">X</span><span class="o">]</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">X</span> <span class="kd">example</span> <span class="o">{</span><span class="n">R</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">CommRing</span> <span class="n">R</span><span class="o">]</span> <span class="o">:</span> <span class="n">R</span><span class="o">[</span><span class="n">X</span><span class="o">]</span> <span class="o">:=</span> <span class="n">X</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">R</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">CommRing</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">r</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="n">r</span> <span class="kd">example</span> <span class="o">{</span><span class="n">R</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">CommRing</span> <span class="n">R</span><span class="o">]</span> <span class="o">(</span><span class="n">r</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="o">:=</span> <span class="n">X</span> <span class="bp">-</span> <span class="n">C</span> <span class="n">r</span> </pre></div> </div> <p>In the first example above, it is crucial that we give Lean the expected type since it cannot be
-
@@ -981,15 +977,15 @@ algebra can be inferred from our use of <code class="docutils literal notranslat<p>Because <code class="docutils literal notranslate"><span class="pre">C</span></code> is a ring morphism from <code class="docutils literal notranslate"><span class="pre">R</span></code> to <code class="docutils literal notranslate"><span class="pre">R[X]</span></code>, we can use all ring morphisms lemmas such as <code class="docutils literal notranslate"><span class="pre">map_zero</span></code>, <code class="docutils literal notranslate"><span class="pre">map_one</span></code>, <code class="docutils literal notranslate"><span class="pre">map_mul</span></code>, and <code class="docutils literal notranslate"><span class="pre">map_pow</span></code> before computing in the ring <code class="docutils literal notranslate"><span class="pre">R[X]</span></code>. For example:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">R</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">CommRing</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">r</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">X</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="n">r</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">X</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="n">r</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="o">(</span><span class="n">r</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">C.map_pow</span><span class="o">]</span> <span class="w"> </span><span class="n">ring</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">R</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">CommRing</span> <span class="n">R</span><span class="o">]</span> <span class="o">(</span><span class="n">r</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">X</span> <span class="bp">+</span> <span class="n">C</span> <span class="n">r</span><span class="o">)</span> <span class="bp">*</span> <span class="o">(</span><span class="n">X</span> <span class="bp">-</span> <span class="n">C</span> <span class="n">r</span><span class="o">)</span> <span class="bp">=</span> <span class="n">X</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">-</span> <span class="n">C</span> <span class="o">(</span><span class="n">r</span> <span class="bp">^</span> <span class="mi">2</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">C.map_pow</span><span class="o">]</span> <span class="n">ring</span> </pre></div> </div> <p>You can access coefficients using <code class="docutils literal notranslate"><span class="pre">Polynomial.coeff</span></code></p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">R</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">CommRing</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">r</span><span class="o">:</span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">C</span><span class="w"> </span><span class="n">r</span><span class="o">)</span><span class="bp">.</span><span class="n">coeff</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">simp</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">R</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">CommRing</span> <span class="n">R</span><span class="o">]</span> <span class="o">(</span><span class="n">r</span><span class="o">:</span><span class="n">R</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">C</span> <span class="n">r</span><span class="o">)</span><span class="bp">.</span><span class="n">coeff</span> <span class="mi">0</span> <span class="bp">=</span> <span class="n">r</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">R</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">CommRing</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">X</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">[</span><span class="n">X</span><span class="o">])</span><span class="bp">.</span><span class="n">coeff</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">simp</span> <span class="kd">example</span> <span class="o">{</span><span class="n">R</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">CommRing</span> <span class="n">R</span><span class="o">]</span> <span class="o">:</span> <span class="o">(</span><span class="n">X</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">+</span> <span class="mi">2</span> <span class="bp">*</span> <span class="n">X</span> <span class="bp">+</span> <span class="n">C</span> <span class="mi">3</span> <span class="o">:</span> <span class="n">R</span><span class="o">[</span><span class="n">X</span><span class="o">])</span><span class="bp">.</span><span class="n">coeff</span> <span class="mi">1</span> <span class="bp">=</span> <span class="mi">2</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> </pre></div> </div> <p>Defining the degree of a polynomial is always tricky because of the special case of the zero
-
@@ -1001,36 +997,36 @@ degree of the zero polynomial, and it is absorbent for addition. (It is almost amultiplication, except that <code class="docutils literal notranslate"><span class="pre">⊥</span> <span class="pre">*</span> <span class="pre">0</span> <span class="pre">=</span> <span class="pre">0</span></code>.)</p> <p>Morally speaking, the <code class="docutils literal notranslate"><span class="pre">degree</span></code> version is the correct one. For instance, it allows us to state the expected formula for the degree of a product (assuming the base ring has no zero divisor).</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">R</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Semiring</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">NoZeroDivisors</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">p</span><span class="w"> </span><span class="n">q</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">[</span><span class="n">X</span><span class="o">]}</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">degree</span><span class="w"> </span><span class="o">(</span><span class="n">p</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">q</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">degree</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">degree</span><span class="w"> </span><span class="n">q</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Polynomial.degree_mul</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">R</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Semiring</span> <span class="n">R</span><span class="o">]</span> <span class="o">[</span><span class="n">NoZeroDivisors</span> <span class="n">R</span><span class="o">]</span> <span class="o">{</span><span class="n">p</span> <span class="n">q</span> <span class="o">:</span> <span class="n">R</span><span class="o">[</span><span class="n">X</span><span class="o">]}</span> <span class="o">:</span> <span class="n">degree</span> <span class="o">(</span><span class="n">p</span> <span class="bp">*</span> <span class="n">q</span><span class="o">)</span> <span class="bp">=</span> <span class="n">degree</span> <span class="n">p</span> <span class="bp">+</span> <span class="n">degree</span> <span class="n">q</span> <span class="o">:=</span> <span class="n">Polynomial.degree_mul</span> </pre></div> </div> <p>Whereas the version for <code class="docutils literal notranslate"><span class="pre">natDegree</span></code> needs to assume non-zero polynomials.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">R</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Semiring</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">NoZeroDivisors</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">p</span><span class="w"> </span><span class="n">q</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">[</span><span class="n">X</span><span class="o">]}</span><span class="w"> </span><span class="o">(</span><span class="n">hp</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hq</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">q</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="mi">0</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">natDegree</span><span class="w"> </span><span class="o">(</span><span class="n">p</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">q</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">natDegree</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">natDegree</span><span class="w"> </span><span class="n">q</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Polynomial.natDegree_mul</span><span class="w"> </span><span class="n">hp</span><span class="w"> </span><span class="n">hq</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">R</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Semiring</span> <span class="n">R</span><span class="o">]</span> <span class="o">[</span><span class="n">NoZeroDivisors</span> <span class="n">R</span><span class="o">]</span> <span class="o">{</span><span class="n">p</span> <span class="n">q</span> <span class="o">:</span> <span class="n">R</span><span class="o">[</span><span class="n">X</span><span class="o">]}</span> <span class="o">(</span><span class="n">hp</span> <span class="o">:</span> <span class="n">p</span> <span class="bp">≠</span> <span class="mi">0</span><span class="o">)</span> <span class="o">(</span><span class="n">hq</span> <span class="o">:</span> <span class="n">q</span> <span class="bp">≠</span> <span class="mi">0</span><span class="o">)</span> <span class="o">:</span> <span class="n">natDegree</span> <span class="o">(</span><span class="n">p</span> <span class="bp">*</span> <span class="n">q</span><span class="o">)</span> <span class="bp">=</span> <span class="n">natDegree</span> <span class="n">p</span> <span class="bp">+</span> <span class="n">natDegree</span> <span class="n">q</span> <span class="o">:=</span> <span class="n">Polynomial.natDegree_mul</span> <span class="n">hp</span> <span class="n">hq</span> </pre></div> </div> <p>However, <code class="docutils literal notranslate"><span class="pre">ℕ</span></code> is much nicer to use than <code class="docutils literal notranslate"><span class="pre">WithBot</span> <span class="pre">ℕ</span></code>, so Mathlib makes both versions available and provides lemmas to convert between them. Also, <code class="docutils literal notranslate"><span class="pre">natDegree</span></code> is the more convenient definition to use when computing the degree of a composition. Composition of polynomial is <code class="docutils literal notranslate"><span class="pre">Polynomial.comp</span></code> and we have:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">R</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Semiring</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">NoZeroDivisors</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">p</span><span class="w"> </span><span class="n">q</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">[</span><span class="n">X</span><span class="o">]}</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">natDegree</span><span class="w"> </span><span class="o">(</span><span class="n">comp</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="n">q</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">natDegree</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">natDegree</span><span class="w"> </span><span class="n">q</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Polynomial.natDegree_comp</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">R</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Semiring</span> <span class="n">R</span><span class="o">]</span> <span class="o">[</span><span class="n">NoZeroDivisors</span> <span class="n">R</span><span class="o">]</span> <span class="o">{</span><span class="n">p</span> <span class="n">q</span> <span class="o">:</span> <span class="n">R</span><span class="o">[</span><span class="n">X</span><span class="o">]}</span> <span class="o">:</span> <span class="n">natDegree</span> <span class="o">(</span><span class="n">comp</span> <span class="n">p</span> <span class="n">q</span><span class="o">)</span> <span class="bp">=</span> <span class="n">natDegree</span> <span class="n">p</span> <span class="bp">*</span> <span class="n">natDegree</span> <span class="n">q</span> <span class="o">:=</span> <span class="n">Polynomial.natDegree_comp</span> </pre></div> </div> <p>Polynomials give rise to polynomial functions: any polynomial can be evaluated on <code class="docutils literal notranslate"><span class="pre">R</span></code> using <code class="docutils literal notranslate"><span class="pre">Polynomial.eval</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">R</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">CommRing</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">P</span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">[</span><span class="n">X</span><span class="o">])</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">P.eval</span><span class="w"> </span><span class="n">x</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">R</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">CommRing</span> <span class="n">R</span><span class="o">]</span> <span class="o">(</span><span class="n">P</span><span class="o">:</span> <span class="n">R</span><span class="o">[</span><span class="n">X</span><span class="o">])</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="o">:=</span> <span class="n">P.eval</span> <span class="n">x</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">R</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">CommRing</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">r</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">X</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="n">r</span><span class="o">)</span><span class="bp">.</span><span class="n">eval</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">simp</span> <span class="kd">example</span> <span class="o">{</span><span class="n">R</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">CommRing</span> <span class="n">R</span><span class="o">]</span> <span class="o">(</span><span class="n">r</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">X</span> <span class="bp">-</span> <span class="n">C</span> <span class="n">r</span><span class="o">)</span><span class="bp">.</span><span class="n">eval</span> <span class="n">r</span> <span class="bp">=</span> <span class="mi">0</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> </pre></div> </div> <p>In particular, there is a predicate, <code class="docutils literal notranslate"><span class="pre">IsRoot</span></code>, that holds for elements <code class="docutils literal notranslate"><span class="pre">r</span></code> in <code class="docutils literal notranslate"><span class="pre">R</span></code> where a polynomial vanishes.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">R</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">CommRing</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">P</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">[</span><span class="n">X</span><span class="o">])</span><span class="w"> </span><span class="o">(</span><span class="n">r</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">IsRoot</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">P.eval</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Iff.rfl</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">R</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">CommRing</span> <span class="n">R</span><span class="o">]</span> <span class="o">(</span><span class="n">P</span> <span class="o">:</span> <span class="n">R</span><span class="o">[</span><span class="n">X</span><span class="o">])</span> <span class="o">(</span><span class="n">r</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="o">:</span> <span class="n">IsRoot</span> <span class="n">P</span> <span class="n">r</span> <span class="bp">↔</span> <span class="n">P.eval</span> <span class="n">r</span> <span class="bp">=</span> <span class="mi">0</span> <span class="o">:=</span> <span class="n">Iff.rfl</span> </pre></div> </div> <p>We would like to say that, assuming <code class="docutils literal notranslate"><span class="pre">R</span></code> has no zero divisor, a polynomial has at most as many
-
@@ -1040,12 +1036,12 @@ So Mathlib defines <code class="docutils literal notranslate"><span class="pre">i.e. the finite set that is defined to be empty if <code class="docutils literal notranslate"><span class="pre">P</span></code> is zero and the roots of <code class="docutils literal notranslate"><span class="pre">P</span></code>, with multiplicities, otherwise. This is defined only when the underlying ring is a domain since otherwise the definition does not have good properties.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">R</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">CommRing</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">IsDomain</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">r</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">X</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="n">r</span><span class="o">)</span><span class="bp">.</span><span class="n">roots</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">{</span><span class="n">r</span><span class="o">}</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">roots_X_sub_C</span><span class="w"> </span><span class="n">r</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">R</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">CommRing</span> <span class="n">R</span><span class="o">]</span> <span class="o">[</span><span class="n">IsDomain</span> <span class="n">R</span><span class="o">]</span> <span class="o">(</span><span class="n">r</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">X</span> <span class="bp">-</span> <span class="n">C</span> <span class="n">r</span><span class="o">)</span><span class="bp">.</span><span class="n">roots</span> <span class="bp">=</span> <span class="o">{</span><span class="n">r</span><span class="o">}</span> <span class="o">:=</span> <span class="n">roots_X_sub_C</span> <span class="n">r</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">R</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">CommRing</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">IsDomain</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">r</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">):</span> <span class="w"> </span><span class="o">((</span><span class="n">X</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="n">r</span><span class="o">)</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="bp">.</span><span class="n">roots</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="o">{</span><span class="n">r</span><span class="o">}</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">simp</span> <span class="kd">example</span> <span class="o">{</span><span class="n">R</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">CommRing</span> <span class="n">R</span><span class="o">]</span> <span class="o">[</span><span class="n">IsDomain</span> <span class="n">R</span><span class="o">]</span> <span class="o">(</span><span class="n">r</span> <span class="o">:</span> <span class="n">R</span><span class="o">)</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">):</span> <span class="o">((</span><span class="n">X</span> <span class="bp">-</span> <span class="n">C</span> <span class="n">r</span><span class="o">)</span> <span class="bp">^</span> <span class="n">n</span><span class="o">)</span><span class="bp">.</span><span class="n">roots</span> <span class="bp">=</span> <span class="n">n</span> <span class="bp">•</span> <span class="o">{</span><span class="n">r</span><span class="o">}</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> </pre></div> </div> <p>Both <code class="docutils literal notranslate"><span class="pre">Polynomial.eval</span></code> and <code class="docutils literal notranslate"><span class="pre">Polynomial.roots</span></code> consider only the coefficients ring. They do not
-
@@ -1056,38 +1052,38 @@ every element of <code class="docutils literal notranslate"><span class="pre">a<has a coercion to functions, one can apply it to a polynomial. But <code class="docutils literal notranslate"><span class="pre">aeval</span></code> does not have a polynomial as an argument, so one cannot use dot notation like in <code class="docutils literal notranslate"><span class="pre">P.eval</span></code> above.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">aeval</span><span class="w"> </span><span class="n">Complex.I</span><span class="w"> </span><span class="o">(</span><span class="n">X</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">[</span><span class="n">X</span><span class="o">])</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">simp</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">aeval</span> <span class="n">Complex.I</span> <span class="o">(</span><span class="n">X</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">+</span> <span class="mi">1</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">[</span><span class="n">X</span><span class="o">])</span> <span class="bp">=</span> <span class="mi">0</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> </pre></div> </div> <p>The function corresponding to <code class="docutils literal notranslate"><span class="pre">roots</span></code> in this context is <code class="docutils literal notranslate"><span class="pre">aroots</span></code> which takes a polynomial and then an algebra and outputs a multiset (with the same caveat about the zero polynomial as for <code class="docutils literal notranslate"><span class="pre">roots</span></code>).</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span><span class="w"> </span><span class="n">Complex</span><span class="w"> </span><span class="n">Polynomial</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">aroots</span><span class="w"> </span><span class="o">(</span><span class="n">X</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">[</span><span class="n">X</span><span class="o">])</span><span class="w"> </span><span class="n">ℂ</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">{</span><span class="n">Complex.I</span><span class="o">,</span><span class="w"> </span><span class="bp">-</span><span class="n">I</span><span class="o">}</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="k">suffices</span><span class="w"> </span><span class="n">roots</span><span class="w"> </span><span class="o">(</span><span class="n">X</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℂ</span><span class="o">[</span><span class="n">X</span><span class="o">])</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">{</span><span class="n">I</span><span class="o">,</span><span class="w"> </span><span class="bp">-</span><span class="n">I</span><span class="o">}</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">simpa</span><span class="w"> </span><span class="o">[</span><span class="n">aroots_def</span><span class="o">]</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">factored</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">X</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℂ</span><span class="o">[</span><span class="n">X</span><span class="o">])</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">(</span><span class="n">X</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="n">I</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">X</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="o">(</span><span class="bp">-</span><span class="n">I</span><span class="o">))</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">key</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">C</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℂ</span><span class="o">[</span><span class="n">X</span><span class="o">])</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">-</span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="o">[</span><span class="bp">←</span><span class="w"> </span><span class="n">C_mul</span><span class="o">]</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">C_neg</span><span class="o">]</span> <span class="w"> </span><span class="n">linear_combination</span><span class="w"> </span><span class="n">key</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">p_ne_zero</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">X</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="n">I</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">X</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="o">(</span><span class="bp">-</span><span class="n">I</span><span class="o">))</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">H</span> <span class="w"> </span><span class="n">apply_fun</span><span class="w"> </span><span class="n">eval</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">H</span> <span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="o">[</span><span class="n">eval</span><span class="o">]</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">H</span> <span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="n">only</span><span class="w"> </span><span class="o">[</span><span class="n">factored</span><span class="o">,</span><span class="w"> </span><span class="n">roots_mul</span><span class="w"> </span><span class="n">p_ne_zero</span><span class="o">,</span><span class="w"> </span><span class="n">roots_X_sub_C</span><span class="o">]</span> <span class="w"> </span><span class="n">rfl</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span> <span class="n">Complex</span> <span class="n">Polynomial</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">aroots</span> <span class="o">(</span><span class="n">X</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">+</span> <span class="mi">1</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">[</span><span class="n">X</span><span class="o">])</span> <span class="n">ℂ</span> <span class="bp">=</span> <span class="o">{</span><span class="n">Complex.I</span><span class="o">,</span> <span class="bp">-</span><span class="n">I</span><span class="o">}</span> <span class="o">:=</span> <span class="kd">by</span> <span class="k">suffices</span> <span class="n">roots</span> <span class="o">(</span><span class="n">X</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">+</span> <span class="mi">1</span> <span class="o">:</span> <span class="n">ℂ</span><span class="o">[</span><span class="n">X</span><span class="o">])</span> <span class="bp">=</span> <span class="o">{</span><span class="n">I</span><span class="o">,</span> <span class="bp">-</span><span class="n">I</span><span class="o">}</span> <span class="kd">by</span> <span class="n">simpa</span> <span class="o">[</span><span class="n">aroots_def</span><span class="o">]</span> <span class="k">have</span> <span class="n">factored</span> <span class="o">:</span> <span class="o">(</span><span class="n">X</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">+</span> <span class="mi">1</span> <span class="o">:</span> <span class="n">ℂ</span><span class="o">[</span><span class="n">X</span><span class="o">])</span> <span class="bp">=</span> <span class="o">(</span><span class="n">X</span> <span class="bp">-</span> <span class="n">C</span> <span class="n">I</span><span class="o">)</span> <span class="bp">*</span> <span class="o">(</span><span class="n">X</span> <span class="bp">-</span> <span class="n">C</span> <span class="o">(</span><span class="bp">-</span><span class="n">I</span><span class="o">))</span> <span class="o">:=</span> <span class="kd">by</span> <span class="k">have</span> <span class="n">key</span> <span class="o">:</span> <span class="o">(</span><span class="n">C</span> <span class="n">I</span> <span class="bp">*</span> <span class="n">C</span> <span class="n">I</span> <span class="o">:</span> <span class="n">ℂ</span><span class="o">[</span><span class="n">X</span><span class="o">])</span> <span class="bp">=</span> <span class="bp">-</span><span class="mi">1</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> <span class="o">[</span><span class="bp">←</span> <span class="n">C_mul</span><span class="o">]</span> <span class="n">rw</span> <span class="o">[</span><span class="n">C_neg</span><span class="o">]</span> <span class="n">linear_combination</span> <span class="n">key</span> <span class="k">have</span> <span class="n">p_ne_zero</span> <span class="o">:</span> <span class="o">(</span><span class="n">X</span> <span class="bp">-</span> <span class="n">C</span> <span class="n">I</span><span class="o">)</span> <span class="bp">*</span> <span class="o">(</span><span class="n">X</span> <span class="bp">-</span> <span class="n">C</span> <span class="o">(</span><span class="bp">-</span><span class="n">I</span><span class="o">))</span> <span class="bp">≠</span> <span class="mi">0</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">H</span> <span class="n">apply_fun</span> <span class="n">eval</span> <span class="mi">0</span> <span class="n">at</span> <span class="n">H</span> <span class="n">simp</span> <span class="o">[</span><span class="n">eval</span><span class="o">]</span> <span class="n">at</span> <span class="n">H</span> <span class="n">simp</span> <span class="n">only</span> <span class="o">[</span><span class="n">factored</span><span class="o">,</span> <span class="n">roots_mul</span> <span class="n">p_ne_zero</span><span class="o">,</span> <span class="n">roots_X_sub_C</span><span class="o">]</span> <span class="n">rfl</span> <span class="c1">-- Mathlib knows about D'Alembert-Gauss theorem: ``ℂ`` is algebraically closed.</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">IsAlgClosed</span><span class="w"> </span><span class="n">ℂ</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">inferInstance</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">IsAlgClosed</span> <span class="n">ℂ</span> <span class="o">:=</span> <span class="n">inferInstance</span> </pre></div> </div> <p>More generally, given an ring morphism <code class="docutils literal notranslate"><span class="pre">f</span> <span class="pre">:</span> <span class="pre">R</span> <span class="pre">→+*</span> <span class="pre">S</span></code> one can evaluate <code class="docutils literal notranslate"><span class="pre">P</span> <span class="pre">:</span> <span class="pre">R[X]</span></code> at a point in <code class="docutils literal notranslate"><span class="pre">S</span></code> using <code class="docutils literal notranslate"><span class="pre">Polynomial.eval₂</span></code>. This one produces an actual function from <code class="docutils literal notranslate"><span class="pre">R[X]</span></code> to <code class="docutils literal notranslate"><span class="pre">S</span></code> since it does not assume the existence of a <code class="docutils literal notranslate"><span class="pre">Algebra</span> <span class="pre">R</span> <span class="pre">S</span></code> instance, so dot notation works as you would expect.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">Complex.ofRealHom</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">→+*</span><span class="w"> </span><span class="n">ℂ</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="o">(</span><span class="n">Complex.ofRealHom</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">→+*</span> <span class="n">ℂ</span><span class="o">)</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">X</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">[</span><span class="n">X</span><span class="o">])</span><span class="bp">.</span><span class="n">eval₂</span><span class="w"> </span><span class="n">Complex.ofRealHom</span><span class="w"> </span><span class="n">Complex.I</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">simp</span> <span class="kd">example</span> <span class="o">:</span> <span class="o">(</span><span class="n">X</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">+</span> <span class="mi">1</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">[</span><span class="n">X</span><span class="o">])</span><span class="bp">.</span><span class="n">eval₂</span> <span class="n">Complex.ofRealHom</span> <span class="n">Complex.I</span> <span class="bp">=</span> <span class="mi">0</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> </pre></div> </div> <p>Let us end by mentioning multivariate polynomials briefly. Given a commutative semiring <code class="docutils literal notranslate"><span class="pre">R</span></code>,
-
@@ -1096,10 +1092,10 @@ a type <code class="docutils literal notranslate"><span class="pre">σ</span<code class="docutils literal notranslate"><span class="pre">MvPolynomial.X</span> <span class="pre">i</span></code>. (As usual, one can open the <code class="docutils literal notranslate"><span class="pre">MVPolynomial</span></code> namespace to shorten this to <code class="docutils literal notranslate"><span class="pre">X</span> <span class="pre">i</span></code>.) For instance, if we want two indeterminates we can use <code class="docutils literal notranslate"><span class="pre">Fin</span> <span class="pre">2</span></code> as <code class="docutils literal notranslate"><span class="pre">σ</span></code> and write the polynomial defining the unit circle in <span class="math notranslate nohighlight">\(\mathbb{R}^2`\)</span> as:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span><span class="w"> </span><span class="n">MvPolynomial</span> <code class="docutils literal notranslate"><span class="pre">Fin</span> <span class="pre">2</span></code> as <code class="docutils literal notranslate"><span class="pre">σ</span></code> and write the polynomial defining the unit circle in <span class="math notranslate nohighlight">\(\mathbb{R}^2\)</span> as:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span> <span class="n">MvPolynomial</span> <span class="kd">def</span><span class="w"> </span><span class="n">circleEquation</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">MvPolynomial</span><span class="w"> </span><span class="o">(</span><span class="n">Fin</span><span class="w"> </span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="mi">1</span> <span class="kd">def</span> <span class="n">circleEquation</span> <span class="o">:</span> <span class="n">MvPolynomial</span> <span class="o">(</span><span class="n">Fin</span> <span class="mi">2</span><span class="o">)</span> <span class="n">ℝ</span> <span class="o">:=</span> <span class="n">X</span> <span class="mi">0</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">+</span> <span class="n">X</span> <span class="mi">1</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">-</span> <span class="mi">1</span> </pre></div> </div> <p>Recall that function application has a very high precedence so the expression above is read as
-
@@ -1107,7 +1103,7 @@ For instance, if we want two indeterminates we can useWe can evaluate it to make sure the point with coordinates <span class="math notranslate nohighlight">\((1, 0)\)</span> is on the circle. Recall the <code class="docutils literal notranslate"><span class="pre">![...]</span></code> notation denotes elements of <code class="docutils literal notranslate"><span class="pre">Fin</span> <span class="pre">n</span> <span class="pre">→</span> <span class="pre">X</span></code> for some natural number <code class="docutils literal notranslate"><span class="pre">n</span></code> determined by the number of arguments and some type <code class="docutils literal notranslate"><span class="pre">X</span></code> determined by the type of arguments.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">MvPolynomial.eval</span><span class="w"> </span><span class="bp">!</span><span class="o">[</span><span class="mi">0</span><span class="o">,</span><span class="w"> </span><span class="mi">1</span><span class="o">]</span><span class="w"> </span><span class="n">circleEquation</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="o">[</span><span class="n">circleEquation</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">MvPolynomial.eval</span> <span class="bp">!</span><span class="o">[</span><span class="mi">0</span><span class="o">,</span> <span class="mi">1</span><span class="o">]</span> <span class="n">circleEquation</span> <span class="bp">=</span> <span class="mi">0</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> <span class="o">[</span><span class="n">circleEquation</span><span class="o">]</span> </pre></div> </div> </section>
-
-
-
@@ -1,24 +1,24 @@<!DOCTYPE html> <html class="writer-html5" lang="en" data-content_root="./"> <html class="writer-html5" lang="en" > <head> <meta charset="utf-8" /><meta name="viewport" content="width=device-width, initial-scale=1" /> <meta charset="utf-8" /><meta name="generator" content="Docutils 0.17.1: http://docutils.sourceforge.net/" /> <meta name="viewport" content="width=device-width, initial-scale=1.0" /> <title>9. Linear algebra — Mathematics in Lean 0.1 documentation</title> <link rel="stylesheet" type="text/css" href="_static/pygments.css?v=80d5e7a1" /> <link rel="stylesheet" type="text/css" href="_static/css/theme.css?v=e59714d7" /> <link rel="stylesheet" type="text/css" href="_static/css/custom.css?v=0731ccc3" /> <link rel="stylesheet" href="_static/pygments.css" type="text/css" /> <link rel="stylesheet" href="_static/css/theme.css" type="text/css" /> <link rel="stylesheet" href="_static/css/custom.css" type="text/css" /> <link rel="shortcut icon" href="_static/favicon.ico"/> <script src="_static/jquery.js?v=5d32c60e"></script> <script src="_static/_sphinx_javascript_frameworks_compat.js?v=2cd50e6c"></script> <script src="_static/documentation_options.js?v=2709fde1"></script> <script src="_static/doctools.js?v=9bcbadda"></script> <script src="_static/sphinx_highlight.js?v=dc90522c"></script> <script async="async" src="https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js"></script> <!--[if lt IE 9]> <script src="_static/js/html5shiv.min.js"></script> <![endif]--> <script data-url_root="./" id="documentation_options" src="_static/documentation_options.js"></script> <script src="_static/jquery.js"></script> <script src="_static/underscore.js"></script> <script src="_static/_sphinx_javascript_frameworks_compat.js"></script> <script src="_static/doctools.js"></script> <script async="async" src="https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js"></script> <script src="_static/js/theme.js"></script> <link rel="index" title="Index" href="genindex.html" /> <link rel="search" title="Search" href="search.html" />
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@@ -31,15 +31,11 @@<nav data-toggle="wy-nav-shift" class="wy-nav-side"> <div class="wy-side-scroll"> <div class="wy-side-nav-search" > <a href="index.html" class="icon icon-home"> Mathematics in Lean <a href="index.html" class="icon icon-home"> Mathematics in Lean </a> <div role="search"> <form id="rtd-search-form" class="wy-form" action="search.html" method="get"> <input type="text" name="q" placeholder="Search docs" aria-label="Search docs" /> <input type="text" name="q" placeholder="Search docs" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form>
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@@ -99,8 +95,8 @@<div class="rst-content"> <div role="navigation" aria-label="Page navigation"> <ul class="wy-breadcrumbs"> <li><a href="index.html" class="icon icon-home" aria-label="Home"></a></li> <li class="breadcrumb-item active"><span class="section-number">9. </span>Linear algebra</li> <li><a href="index.html" class="icon icon-home"></a> »</li> <li><span class="section-number">9. </span>Linear algebra</li> <li class="wy-breadcrumbs-aside"> <a href="_sources/C09_Linear_Algebra.rst.txt" rel="nofollow"> View page source</a> </li>
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@@ -111,11 +107,11 @@<div itemprop="articleBody"> <section id="linear-algebra"> <span id="id1"></span><h1><span class="section-number">9. </span>Linear algebra<a class="headerlink" href="#linear-algebra" title="Link to this heading"></a></h1> <span id="id1"></span><h1><span class="section-number">9. </span>Linear algebra<a class="headerlink" href="#linear-algebra" title="Permalink to this heading"></a></h1> <section id="vector-spaces-and-linear-maps"> <h2><span class="section-number">9.1. </span>Vector spaces and linear maps<a class="headerlink" href="#vector-spaces-and-linear-maps" title="Link to this heading"></a></h2> <h2><span class="section-number">9.1. </span>Vector spaces and linear maps<a class="headerlink" href="#vector-spaces-and-linear-maps" title="Permalink to this heading"></a></h2> <section id="vector-spaces"> <h3><span class="section-number">9.1.1. </span>Vector spaces<a class="headerlink" href="#vector-spaces" title="Link to this heading"></a></h3> <h3><span class="section-number">9.1.1. </span>Vector spaces<a class="headerlink" href="#vector-spaces" title="Permalink to this heading"></a></h3> <p id="index-0">We will start directly abstract linear algebra, taking place in a vector space over any field. However you can find information about matrices in <a class="reference internal" href="#matrices"><span class="std std-numref">Section 9.4.1</span></a> which does not logically depend on this abstract theory.
-
@@ -123,7 +119,7 @@ Mathlib actually deals with a more general version of linear algebra involving tbut for now we will pretend this is only an eccentric spelling habit.</p> <p>The way to say “let <span class="math notranslate nohighlight">\(K\)</span> be a field and let <span class="math notranslate nohighlight">\(V\)</span> be a vector space over <span class="math notranslate nohighlight">\(K\)</span>” (and make them implicit arguments to later results) is:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">K</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Field</span><span class="w"> </span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">V</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">AddCommGroup</span><span class="w"> </span><span class="n">V</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Module</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">K</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Field</span> <span class="n">K</span><span class="o">]</span> <span class="o">{</span><span class="n">V</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">AddCommGroup</span> <span class="n">V</span><span class="o">]</span> <span class="o">[</span><span class="n">Module</span> <span class="n">K</span> <span class="n">V</span><span class="o">]</span> </pre></div> </div> <p>We explained in <a class="reference internal" href="C07_Hierarchies.html#hierarchies"><span class="std std-numref">Chapter 7</span></a> why we need two separate
-
@@ -144,14 +140,14 @@ following from the axioms of vector spaces and fields, in the same way the<cite>ring</cite> tactic is used in commutative rings or the <cite>group</cite> tactic is used in groups. But it is still useful to remember that scalar multiplication is abbreviated <cite>smul</cite> in lemma names.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">K</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">u</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="o">(</span><span class="n">u</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">v</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">smul_add</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="n">v</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">K</span><span class="o">)</span> <span class="o">(</span><span class="n">u</span> <span class="n">v</span> <span class="o">:</span> <span class="n">V</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">•</span> <span class="o">(</span><span class="n">u</span> <span class="bp">+</span> <span class="n">v</span><span class="o">)</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">•</span> <span class="n">u</span> <span class="bp">+</span> <span class="n">a</span> <span class="bp">•</span> <span class="n">v</span> <span class="o">:=</span> <span class="n">smul_add</span> <span class="n">a</span> <span class="n">u</span> <span class="n">v</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">K</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">u</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">add_smul</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">u</span> <span class="kd">example</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">K</span><span class="o">)</span> <span class="o">(</span><span class="n">u</span> <span class="o">:</span> <span class="n">V</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">a</span> <span class="bp">+</span> <span class="n">b</span><span class="o">)</span> <span class="bp">•</span> <span class="n">u</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">•</span> <span class="n">u</span> <span class="bp">+</span> <span class="n">b</span> <span class="bp">•</span> <span class="n">u</span> <span class="o">:=</span> <span class="n">add_smul</span> <span class="n">a</span> <span class="n">b</span> <span class="n">u</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">K</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">u</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">smul_comm</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">u</span> <span class="kd">example</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">K</span><span class="o">)</span> <span class="o">(</span><span class="n">u</span> <span class="o">:</span> <span class="n">V</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">•</span> <span class="n">b</span> <span class="bp">•</span> <span class="n">u</span> <span class="bp">=</span> <span class="n">b</span> <span class="bp">•</span> <span class="n">a</span> <span class="bp">•</span> <span class="n">u</span> <span class="o">:=</span> <span class="n">smul_comm</span> <span class="n">a</span> <span class="n">b</span> <span class="n">u</span> </pre></div> </div> <p>As a quick note for more advanced readers, let us point out that, as suggested by
-
@@ -160,14 +156,14 @@ rings.In fact it even covers semi-modules over semi-rings. If you think you do not need this level of generality, you can meditate the following example that nicely captures a lot of algebraic rules about ideals acting on submodules:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">R</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">CommSemiring</span><span class="w"> </span><span class="n">R</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">AddCommMonoid</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Module</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="n">M</span><span class="o">]</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">Module</span><span class="w"> </span><span class="o">(</span><span class="n">Ideal</span><span class="w"> </span><span class="n">R</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">Submodule</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="n">M</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">inferInstance</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">R</span> <span class="n">M</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">CommSemiring</span> <span class="n">R</span><span class="o">]</span> <span class="o">[</span><span class="n">AddCommMonoid</span> <span class="n">M</span><span class="o">]</span> <span class="o">[</span><span class="n">Module</span> <span class="n">R</span> <span class="n">M</span><span class="o">]</span> <span class="o">:</span> <span class="n">Module</span> <span class="o">(</span><span class="n">Ideal</span> <span class="n">R</span><span class="o">)</span> <span class="o">(</span><span class="n">Submodule</span> <span class="n">R</span> <span class="n">M</span><span class="o">)</span> <span class="o">:=</span> <span class="n">inferInstance</span> </pre></div> </div> </section> <section id="linear-maps"> <h3><span class="section-number">9.1.2. </span>Linear maps<a class="headerlink" href="#linear-maps" title="Link to this heading"></a></h3> <h3><span class="section-number">9.1.2. </span>Linear maps<a class="headerlink" href="#linear-maps" title="Permalink to this heading"></a></h3> <p id="index-1">Next we need linear maps. Like group morphisms, linear maps in Mathlib are bundled maps, i.e. packages made of a map and proofs of its linearity properties. Those bundled maps are converted to ordinary functions when applied.
-
@@ -179,31 +175,31 @@ But this is crucial when several fields come into play.For instance real-linear maps from <span class="math notranslate nohighlight">\(ℂ\)</span> to <span class="math notranslate nohighlight">\(ℂ\)</span> are every map <span class="math notranslate nohighlight">\(z ↦ az + b\bar{z}\)</span> while only the maps <span class="math notranslate nohighlight">\(z ↦ az\)</span> are complex linear, and this difference is crucial in complex analysis.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">W</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">AddCommGroup</span><span class="w"> </span><span class="n">W</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Module</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">W</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">W</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">AddCommGroup</span> <span class="n">W</span><span class="o">]</span> <span class="o">[</span><span class="n">Module</span> <span class="n">K</span> <span class="n">W</span><span class="o">]</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">W</span><span class="o">)</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="n">V</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">W</span><span class="o">)</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">K</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">v</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">v</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">map_smul</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">v</span> <span class="kd">example</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">K</span><span class="o">)</span> <span class="o">(</span><span class="n">v</span> <span class="o">:</span> <span class="n">V</span><span class="o">)</span> <span class="o">:</span> <span class="n">φ</span> <span class="o">(</span><span class="n">a</span> <span class="bp">•</span> <span class="n">v</span><span class="o">)</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">•</span> <span class="n">φ</span> <span class="n">v</span> <span class="o">:=</span> <span class="n">map_smul</span> <span class="n">φ</span> <span class="n">a</span> <span class="n">v</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">v</span><span class="w"> </span><span class="n">w</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="o">(</span><span class="n">v</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">w</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">w</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">map_add</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="n">w</span> <span class="kd">example</span> <span class="o">(</span><span class="n">v</span> <span class="n">w</span> <span class="o">:</span> <span class="n">V</span><span class="o">)</span> <span class="o">:</span> <span class="n">φ</span> <span class="o">(</span><span class="n">v</span> <span class="bp">+</span> <span class="n">w</span><span class="o">)</span> <span class="bp">=</span> <span class="n">φ</span> <span class="n">v</span> <span class="bp">+</span> <span class="n">φ</span> <span class="n">w</span> <span class="o">:=</span> <span class="n">map_add</span> <span class="n">φ</span> <span class="n">v</span> <span class="n">w</span> </pre></div> </div> <p>Note that <code class="docutils literal notranslate"><span class="pre">V</span> <span class="pre">→ₗ[K]</span> <span class="pre">W</span></code> itself carries interesting algebraic structures (this is part of the motivation for bundling those maps). It is a <code class="docutils literal notranslate"><span class="pre">K</span></code>-vector space so we can add linear maps and multiply them by scalars.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">ψ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">W</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">(</span><span class="n">ψ</span> <span class="o">:</span> <span class="n">V</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">W</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="mi">2</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">ψ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">W</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="mi">2</span> <span class="bp">•</span> <span class="n">φ</span> <span class="bp">+</span> <span class="n">ψ</span> <span class="o">:</span> <span class="n">V</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">W</span><span class="o">)</span> </pre></div> </div> <p>One downside of using bundled maps is that we cannot use ordinary function composition. We need to use <code class="docutils literal notranslate"><span class="pre">LinearMap.comp</span></code> or the notation <code class="docutils literal notranslate"><span class="pre">∘ₗ</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">θ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">V</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">(</span><span class="n">θ</span> <span class="o">:</span> <span class="n">W</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">V</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">φ.comp</span><span class="w"> </span><span class="n">θ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">W</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="bp">∘ₗ</span><span class="w"> </span><span class="n">θ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">W</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">φ.comp</span> <span class="n">θ</span> <span class="o">:</span> <span class="n">W</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">W</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">φ</span> <span class="bp">∘ₗ</span> <span class="n">θ</span> <span class="o">:</span> <span class="n">W</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">W</span><span class="o">)</span> </pre></div> </div> <p>There are two main ways to construct linear maps.
-
@@ -211,10 +207,10 @@ First we can build the structure by providing the function and the linearity proAs usual, this is facilitated by the structure code action: you can type <code class="docutils literal notranslate"><span class="pre">example</span> <span class="pre">:</span> <span class="pre">V</span> <span class="pre">→ₗ[K]</span> <span class="pre">V</span> <span class="pre">:=</span> <span class="pre">_</span></code> and use the code action “Generate a skeleton” attached to the underscore.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">toFun</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">v</span> <span class="w"> </span><span class="n">map_add'</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">smul_add</span><span class="w"> </span><span class="bp">..</span> <span class="w"> </span><span class="n">map_smul'</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">smul_comm</span><span class="w"> </span><span class="bp">..</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">V</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">V</span> <span class="n">where</span> <span class="n">toFun</span> <span class="n">v</span> <span class="o">:=</span> <span class="mi">3</span> <span class="bp">•</span> <span class="n">v</span> <span class="n">map_add'</span> <span class="n">_</span> <span class="n">_</span> <span class="o">:=</span> <span class="n">smul_add</span> <span class="bp">..</span> <span class="n">map_smul'</span> <span class="n">_</span> <span class="n">_</span> <span class="o">:=</span> <span class="n">smul_comm</span> <span class="bp">..</span> </pre></div> </div> <p>You may wonder why the proof fields of <code class="docutils literal notranslate"><span class="pre">LinearMap</span></code> have names ending with a prime.
-
@@ -227,9 +223,9 @@ linear maps, <code class="docutils literal notranslate"><span class="pre">K</spaThe intermediate version, <code class="docutils literal notranslate"><span class="pre">LinearMap.map_add</span></code> is a bit redundant but allows to use dot notation, which can be nice sometimes. A similar story exists for <code class="docutils literal notranslate"><span class="pre">map_smul</span></code>, and the general framework is explained in <a class="reference internal" href="C07_Hierarchies.html#hierarchies"><span class="std std-numref">Chapter 7</span></a>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">φ.map_add'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="o">,</span><span class="w"> </span><span class="n">φ.toFun</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">φ.toFun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">φ.toFun</span><span class="w"> </span><span class="n">y</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">φ.map_add</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="o">,</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">y</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">map_add</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="o">,</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">y</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="o">(</span><span class="n">φ.map_add'</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">V</span><span class="o">,</span> <span class="n">φ.toFun</span> <span class="o">(</span><span class="n">x</span> <span class="bp">+</span> <span class="n">y</span><span class="o">)</span> <span class="bp">=</span> <span class="n">φ.toFun</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">φ.toFun</span> <span class="n">y</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">φ.map_add</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">V</span><span class="o">,</span> <span class="n">φ</span> <span class="o">(</span><span class="n">x</span> <span class="bp">+</span> <span class="n">y</span><span class="o">)</span> <span class="bp">=</span> <span class="n">φ</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">φ</span> <span class="n">y</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">map_add</span> <span class="n">φ</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">V</span><span class="o">,</span> <span class="n">φ</span> <span class="o">(</span><span class="n">x</span> <span class="bp">+</span> <span class="n">y</span><span class="o">)</span> <span class="bp">=</span> <span class="n">φ</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">φ</span> <span class="n">y</span><span class="o">)</span> </pre></div> </div> <p>One can also build linear maps from the ones that are already defined in Mathlib
-
@@ -241,8 +237,8 @@ for Lean to infer <code class="docutils literal notranslate"><span class="pre">VBut also <code class="docutils literal notranslate"><span class="pre">LinearMap.lsmul</span> <span class="pre">K</span> <span class="pre">V</span></code> is an interesting object by itself: it has type <code class="docutils literal notranslate"><span class="pre">K</span> <span class="pre">→ₗ[K]</span> <span class="pre">V</span> <span class="pre">→ₗ[K]</span> <span class="pre">V</span></code>, meaning it is a <code class="docutils literal notranslate"><span class="pre">K</span></code>-linear map from <code class="docutils literal notranslate"><span class="pre">K</span></code> —seen as a vector space over itself— to the space of <code class="docutils literal notranslate"><span class="pre">K</span></code>-linear maps from <code class="docutils literal notranslate"><span class="pre">V</span></code> to <code class="docutils literal notranslate"><span class="pre">V</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">LinearMap.lsmul</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">V</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">LinearMap.lsmul</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">V</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="o">(</span><span class="n">LinearMap.lsmul</span> <span class="n">K</span> <span class="n">V</span> <span class="mi">3</span> <span class="o">:</span> <span class="n">V</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">V</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">LinearMap.lsmul</span> <span class="n">K</span> <span class="n">V</span> <span class="o">:</span> <span class="n">K</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">V</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">V</span><span class="o">)</span> </pre></div> </div> <p>There is also a type <code class="docutils literal notranslate"><span class="pre">LinearEquiv</span></code> of linear isomorphisms denoted by <code class="docutils literal notranslate"><span class="pre">V</span> <span class="pre">≃ₗ[K]</span> <span class="pre">W</span></code>.
-
@@ -250,21 +246,21 @@ The inverse of <code class="docutils literal notranslate"><span class="pre">f</scomposition of <code class="docutils literal notranslate"><span class="pre">f</span></code> and <code class="docutils literal notranslate"><span class="pre">g</span></code> is <code class="docutils literal notranslate"><span class="pre">f.trans</span> <span class="pre">g</span></code> also denoted by <code class="docutils literal notranslate"><span class="pre">f</span> <span class="pre">≪≫ₗ</span> <span class="pre">g</span></code>, and the identity isomorphism of <code class="docutils literal notranslate"><span class="pre">V</span></code> is <code class="docutils literal notranslate"><span class="pre">LinearEquiv.refl</span> <span class="pre">K</span> <span class="pre">V</span></code>. Elements of this type are automatically coerced to morphisms and functions when necessary.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">≃ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">W</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">≪≫ₗ</span><span class="w"> </span><span class="n">f.symm</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">LinearEquiv.refl</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">f.self_trans_symm</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">V</span> <span class="bp">≃ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">W</span><span class="o">)</span> <span class="o">:</span> <span class="n">f</span> <span class="bp">≪≫ₗ</span> <span class="n">f.symm</span> <span class="bp">=</span> <span class="n">LinearEquiv.refl</span> <span class="n">K</span> <span class="n">V</span> <span class="o">:=</span> <span class="n">f.self_trans_symm</span> </pre></div> </div> <p>One can use <code class="docutils literal notranslate"><span class="pre">LinearEquiv.ofBijective</span></code> to build an isomorphism from a bijective morphism. Doing so makes the inverse function noncomputable.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">noncomputable</span><span class="w"> </span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">W</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Function.Bijective</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">≃ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="bp">.</span><span class="n">ofBijective</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">h</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">noncomputable</span> <span class="kd">example</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">V</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">W</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">Function.Bijective</span> <span class="n">f</span><span class="o">)</span> <span class="o">:</span> <span class="n">V</span> <span class="bp">≃ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">W</span> <span class="o">:=</span> <span class="bp">.</span><span class="n">ofBijective</span> <span class="n">f</span> <span class="n">h</span> </pre></div> </div> <p>Note that in the above example, Lean uses the announced type to understand that <code class="docutils literal notranslate"><span class="pre">.ofBijective</span></code> refers to <code class="docutils literal notranslate"><span class="pre">LinearEquiv.ofBijective</span></code> (without needing to open any namespace).</p> </section> <section id="sums-and-products-of-vector-spaces"> <h3><span class="section-number">9.1.3. </span>Sums and products of vector spaces<a class="headerlink" href="#sums-and-products-of-vector-spaces" title="Link to this heading"></a></h3> <h3><span class="section-number">9.1.3. </span>Sums and products of vector spaces<a class="headerlink" href="#sums-and-products-of-vector-spaces" title="Permalink to this heading"></a></h3> <p>We can build new vector spaces out of old ones using direct sums and direct products. Let us start with two vectors spaces. In this case there is no difference between sum and product,
-
@@ -274,57 +270,57 @@ and projections) as linear maps, as well as the universal properties constructininto products and out of sums (if you are not familiar with the category-theoretic distinction between sums and products, you can simply ignore the universal property vocabulary and focus on the types of the following examples).</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">section</span><span class="w"> </span><span class="n">binary_product</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">section</span> <span class="n">binary_product</span> <span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">W</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">AddCommGroup</span><span class="w"> </span><span class="n">W</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Module</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">W</span><span class="o">]</span> <span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">U</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">AddCommGroup</span><span class="w"> </span><span class="n">U</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Module</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">U</span><span class="o">]</span> <span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">T</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">AddCommGroup</span><span class="w"> </span><span class="n">T</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Module</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">T</span><span class="o">]</span> <span class="kd">variable</span> <span class="o">{</span><span class="n">W</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">AddCommGroup</span> <span class="n">W</span><span class="o">]</span> <span class="o">[</span><span class="n">Module</span> <span class="n">K</span> <span class="n">W</span><span class="o">]</span> <span class="kd">variable</span> <span class="o">{</span><span class="n">U</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">AddCommGroup</span> <span class="n">U</span><span class="o">]</span> <span class="o">[</span><span class="n">Module</span> <span class="n">K</span> <span class="n">U</span><span class="o">]</span> <span class="kd">variable</span> <span class="o">{</span><span class="n">T</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">AddCommGroup</span> <span class="n">T</span><span class="o">]</span> <span class="o">[</span><span class="n">Module</span> <span class="n">K</span> <span class="n">T</span><span class="o">]</span> <span class="c1">-- First projection map</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">×</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">LinearMap.fst</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="n">W</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">V</span> <span class="bp">×</span> <span class="n">W</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">V</span> <span class="o">:=</span> <span class="n">LinearMap.fst</span> <span class="n">K</span> <span class="n">V</span> <span class="n">W</span> <span class="c1">-- Second projection map</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">×</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">LinearMap.snd</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="n">W</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">V</span> <span class="bp">×</span> <span class="n">W</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">W</span> <span class="o">:=</span> <span class="n">LinearMap.snd</span> <span class="n">K</span> <span class="n">V</span> <span class="n">W</span> <span class="c1">-- Universal property of the product</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">U</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">ψ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">U</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">W</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">U</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">×</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">LinearMap.prod</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">ψ</span> <span class="kd">example</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="n">U</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">V</span><span class="o">)</span> <span class="o">(</span><span class="n">ψ</span> <span class="o">:</span> <span class="n">U</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">W</span><span class="o">)</span> <span class="o">:</span> <span class="n">U</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">V</span> <span class="bp">×</span> <span class="n">W</span> <span class="o">:=</span> <span class="n">LinearMap.prod</span> <span class="n">φ</span> <span class="n">ψ</span> <span class="c1">-- The product map does the expected thing, first component</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">U</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">ψ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">U</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">W</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">LinearMap.fst</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="bp">∘ₗ</span><span class="w"> </span><span class="n">LinearMap.prod</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">ψ</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">rfl</span> <span class="kd">example</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="n">U</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">V</span><span class="o">)</span> <span class="o">(</span><span class="n">ψ</span> <span class="o">:</span> <span class="n">U</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">W</span><span class="o">)</span> <span class="o">:</span> <span class="n">LinearMap.fst</span> <span class="n">K</span> <span class="n">V</span> <span class="n">W</span> <span class="bp">∘ₗ</span> <span class="n">LinearMap.prod</span> <span class="n">φ</span> <span class="n">ψ</span> <span class="bp">=</span> <span class="n">φ</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="c1">-- The product map does the expected thing, second component</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">U</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">ψ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">U</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">W</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">LinearMap.snd</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="bp">∘ₗ</span><span class="w"> </span><span class="n">LinearMap.prod</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">ψ</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">ψ</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">rfl</span> <span class="kd">example</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="n">U</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">V</span><span class="o">)</span> <span class="o">(</span><span class="n">ψ</span> <span class="o">:</span> <span class="n">U</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">W</span><span class="o">)</span> <span class="o">:</span> <span class="n">LinearMap.snd</span> <span class="n">K</span> <span class="n">V</span> <span class="n">W</span> <span class="bp">∘ₗ</span> <span class="n">LinearMap.prod</span> <span class="n">φ</span> <span class="n">ψ</span> <span class="bp">=</span> <span class="n">ψ</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="c1">-- We can also combine maps in parallel</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">U</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">ψ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">T</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">V</span><span class="w"> </span><span class="bp">×</span><span class="w"> </span><span class="n">W</span><span class="o">)</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">U</span><span class="w"> </span><span class="bp">×</span><span class="w"> </span><span class="n">T</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">φ.prodMap</span><span class="w"> </span><span class="n">ψ</span> <span class="kd">example</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="n">V</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">U</span><span class="o">)</span> <span class="o">(</span><span class="n">ψ</span> <span class="o">:</span> <span class="n">W</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">T</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">V</span> <span class="bp">×</span> <span class="n">W</span><span class="o">)</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="o">(</span><span class="n">U</span> <span class="bp">×</span> <span class="n">T</span><span class="o">)</span> <span class="o">:=</span> <span class="n">φ.prodMap</span> <span class="n">ψ</span> <span class="c1">-- This is simply done by combining the projections with the universal property</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">U</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">ψ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">T</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">φ.prodMap</span><span class="w"> </span><span class="n">ψ</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="bp">∘ₗ</span><span class="w"> </span><span class="bp">.</span><span class="n">fst</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="n">W</span><span class="o">)</span><span class="bp">.</span><span class="n">prod</span><span class="w"> </span><span class="o">(</span><span class="n">ψ</span><span class="w"> </span><span class="bp">∘ₗ</span><span class="w"> </span><span class="bp">.</span><span class="n">snd</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="n">W</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">rfl</span> <span class="kd">example</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="n">V</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">U</span><span class="o">)</span> <span class="o">(</span><span class="n">ψ</span> <span class="o">:</span> <span class="n">W</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">T</span><span class="o">)</span> <span class="o">:</span> <span class="n">φ.prodMap</span> <span class="n">ψ</span> <span class="bp">=</span> <span class="o">(</span><span class="n">φ</span> <span class="bp">∘ₗ</span> <span class="bp">.</span><span class="n">fst</span> <span class="n">K</span> <span class="n">V</span> <span class="n">W</span><span class="o">)</span><span class="bp">.</span><span class="n">prod</span> <span class="o">(</span><span class="n">ψ</span> <span class="bp">∘ₗ</span> <span class="bp">.</span><span class="n">snd</span> <span class="n">K</span> <span class="n">V</span> <span class="n">W</span><span class="o">)</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="c1">-- First inclusion map</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">×</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">LinearMap.inl</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="n">W</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">V</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">V</span> <span class="bp">×</span> <span class="n">W</span> <span class="o">:=</span> <span class="n">LinearMap.inl</span> <span class="n">K</span> <span class="n">V</span> <span class="n">W</span> <span class="c1">-- Second inclusion map</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">×</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">LinearMap.inr</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="n">W</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">W</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">V</span> <span class="bp">×</span> <span class="n">W</span> <span class="o">:=</span> <span class="n">LinearMap.inr</span> <span class="n">K</span> <span class="n">V</span> <span class="n">W</span> <span class="c1">-- Universal property of the sum (aka coproduct)</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">U</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">ψ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">U</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">×</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">U</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">φ.coprod</span><span class="w"> </span><span class="n">ψ</span> <span class="kd">example</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="n">V</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">U</span><span class="o">)</span> <span class="o">(</span><span class="n">ψ</span> <span class="o">:</span> <span class="n">W</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">U</span><span class="o">)</span> <span class="o">:</span> <span class="n">V</span> <span class="bp">×</span> <span class="n">W</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">U</span> <span class="o">:=</span> <span class="n">φ.coprod</span> <span class="n">ψ</span> <span class="c1">-- The coproduct map does the expected thing, first component</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">U</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">ψ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">U</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">φ.coprod</span><span class="w"> </span><span class="n">ψ</span><span class="w"> </span><span class="bp">∘ₗ</span><span class="w"> </span><span class="n">LinearMap.inl</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">LinearMap.coprod_inl</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">ψ</span> <span class="kd">example</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="n">V</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">U</span><span class="o">)</span> <span class="o">(</span><span class="n">ψ</span> <span class="o">:</span> <span class="n">W</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">U</span><span class="o">)</span> <span class="o">:</span> <span class="n">φ.coprod</span> <span class="n">ψ</span> <span class="bp">∘ₗ</span> <span class="n">LinearMap.inl</span> <span class="n">K</span> <span class="n">V</span> <span class="n">W</span> <span class="bp">=</span> <span class="n">φ</span> <span class="o">:=</span> <span class="n">LinearMap.coprod_inl</span> <span class="n">φ</span> <span class="n">ψ</span> <span class="c1">-- The coproduct map does the expected thing, second component</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">U</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">ψ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">U</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">φ.coprod</span><span class="w"> </span><span class="n">ψ</span><span class="w"> </span><span class="bp">∘ₗ</span><span class="w"> </span><span class="n">LinearMap.inr</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">ψ</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">LinearMap.coprod_inr</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">ψ</span> <span class="kd">example</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="n">V</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">U</span><span class="o">)</span> <span class="o">(</span><span class="n">ψ</span> <span class="o">:</span> <span class="n">W</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">U</span><span class="o">)</span> <span class="o">:</span> <span class="n">φ.coprod</span> <span class="n">ψ</span> <span class="bp">∘ₗ</span> <span class="n">LinearMap.inr</span> <span class="n">K</span> <span class="n">V</span> <span class="n">W</span> <span class="bp">=</span> <span class="n">ψ</span> <span class="o">:=</span> <span class="n">LinearMap.coprod_inr</span> <span class="n">φ</span> <span class="n">ψ</span> <span class="c1">-- The coproduct map is defined in the expected way</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">U</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">ψ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">U</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">v</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">w</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">W</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">φ.coprod</span><span class="w"> </span><span class="n">ψ</span><span class="w"> </span><span class="o">(</span><span class="n">v</span><span class="o">,</span><span class="w"> </span><span class="n">w</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">ψ</span><span class="w"> </span><span class="n">w</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">example</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="n">V</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">U</span><span class="o">)</span> <span class="o">(</span><span class="n">ψ</span> <span class="o">:</span> <span class="n">W</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">U</span><span class="o">)</span> <span class="o">(</span><span class="n">v</span> <span class="o">:</span> <span class="n">V</span><span class="o">)</span> <span class="o">(</span><span class="n">w</span> <span class="o">:</span> <span class="n">W</span><span class="o">)</span> <span class="o">:</span> <span class="n">φ.coprod</span> <span class="n">ψ</span> <span class="o">(</span><span class="n">v</span><span class="o">,</span> <span class="n">w</span><span class="o">)</span> <span class="bp">=</span> <span class="n">φ</span> <span class="n">v</span> <span class="bp">+</span> <span class="n">ψ</span> <span class="n">w</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="kd">end</span><span class="w"> </span><span class="n">binary_product</span> <span class="kd">end</span> <span class="n">binary_product</span> </pre></div> </div> <p>Let us now turn to sums and products of arbitrary families of vector spaces.
-
@@ -333,57 +329,57 @@ properties of sums and products.Note that the direct sum notation is scoped to the <code class="docutils literal notranslate"><span class="pre">DirectSum</span></code> namespace, and that the universal property of direct sums requires decidable equality on the indexing type (this is somehow an implementation accident).</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">section</span><span class="w"> </span><span class="n">families</span> <span class="kn">open</span><span class="w"> </span><span class="n">DirectSum</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">section</span> <span class="n">families</span> <span class="kn">open</span> <span class="n">DirectSum</span> <span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">ι</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">DecidableEq</span><span class="w"> </span><span class="n">ι</span><span class="o">]</span> <span class="w"> </span><span class="o">(</span><span class="n">V</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="bp">∀</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">AddCommGroup</span><span class="w"> </span><span class="o">(</span><span class="n">V</span><span class="w"> </span><span class="n">i</span><span class="o">)]</span><span class="w"> </span><span class="o">[</span><span class="bp">∀</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">Module</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="o">(</span><span class="n">V</span><span class="w"> </span><span class="n">i</span><span class="o">)]</span> <span class="kd">variable</span> <span class="o">{</span><span class="n">ι</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">DecidableEq</span> <span class="n">ι</span><span class="o">]</span> <span class="o">(</span><span class="n">V</span> <span class="o">:</span> <span class="n">ι</span> <span class="bp">→</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">)</span> <span class="o">[</span><span class="bp">∀</span> <span class="n">i</span><span class="o">,</span> <span class="n">AddCommGroup</span> <span class="o">(</span><span class="n">V</span> <span class="n">i</span><span class="o">)]</span> <span class="o">[</span><span class="bp">∀</span> <span class="n">i</span><span class="o">,</span> <span class="n">Module</span> <span class="n">K</span> <span class="o">(</span><span class="n">V</span> <span class="n">i</span><span class="o">)]</span> <span class="c1">-- The universal property of the direct sum assembles maps from the summands to build</span> <span class="c1">-- a map from the direct sum</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">Π</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="o">(</span><span class="n">V</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">W</span><span class="o">))</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="bp">⨁</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">DirectSum.toModule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="n">φ</span> <span class="kd">example</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="bp">Π</span> <span class="n">i</span><span class="o">,</span> <span class="o">(</span><span class="n">V</span> <span class="n">i</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">W</span><span class="o">))</span> <span class="o">:</span> <span class="o">(</span><span class="bp">⨁</span> <span class="n">i</span><span class="o">,</span> <span class="n">V</span> <span class="n">i</span><span class="o">)</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">W</span> <span class="o">:=</span> <span class="n">DirectSum.toModule</span> <span class="n">K</span> <span class="n">ι</span> <span class="n">W</span> <span class="n">φ</span> <span class="c1">-- The universal property of the direct product assembles maps into the factors</span> <span class="c1">-- to build a map into the direct product</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">Π</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="o">(</span><span class="n">W</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="n">i</span><span class="o">))</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="bp">Π</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">LinearMap.pi</span><span class="w"> </span><span class="n">φ</span> <span class="kd">example</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="bp">Π</span> <span class="n">i</span><span class="o">,</span> <span class="o">(</span><span class="n">W</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">V</span> <span class="n">i</span><span class="o">))</span> <span class="o">:</span> <span class="n">W</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="o">(</span><span class="bp">Π</span> <span class="n">i</span><span class="o">,</span> <span class="n">V</span> <span class="n">i</span><span class="o">)</span> <span class="o">:=</span> <span class="n">LinearMap.pi</span> <span class="n">φ</span> <span class="c1">-- The projection maps from the product</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">i</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="bp">Π</span><span class="w"> </span><span class="n">j</span><span class="o">,</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="n">j</span><span class="o">)</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">LinearMap.proj</span><span class="w"> </span><span class="n">i</span> <span class="kd">example</span> <span class="o">(</span><span class="n">i</span> <span class="o">:</span> <span class="n">ι</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="bp">Π</span> <span class="n">j</span><span class="o">,</span> <span class="n">V</span> <span class="n">j</span><span class="o">)</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">V</span> <span class="n">i</span> <span class="o">:=</span> <span class="n">LinearMap.proj</span> <span class="n">i</span> <span class="c1">-- The inclusion maps into the sum</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">i</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="bp">⨁</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">DirectSum.lof</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="n">i</span> <span class="kd">example</span> <span class="o">(</span><span class="n">i</span> <span class="o">:</span> <span class="n">ι</span><span class="o">)</span> <span class="o">:</span> <span class="n">V</span> <span class="n">i</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="o">(</span><span class="bp">⨁</span> <span class="n">i</span><span class="o">,</span> <span class="n">V</span> <span class="n">i</span><span class="o">)</span> <span class="o">:=</span> <span class="n">DirectSum.lof</span> <span class="n">K</span> <span class="n">ι</span> <span class="n">V</span> <span class="n">i</span> <span class="c1">-- The inclusion maps into the product</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">i</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="bp">Π</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">LinearMap.single</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="n">i</span> <span class="kd">example</span> <span class="o">(</span><span class="n">i</span> <span class="o">:</span> <span class="n">ι</span><span class="o">)</span> <span class="o">:</span> <span class="n">V</span> <span class="n">i</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="o">(</span><span class="bp">Π</span> <span class="n">i</span><span class="o">,</span> <span class="n">V</span> <span class="n">i</span><span class="o">)</span> <span class="o">:=</span> <span class="n">LinearMap.single</span> <span class="n">K</span> <span class="n">V</span> <span class="n">i</span> <span class="c1">-- In case `ι` is a finite type, there is an isomorphism between the sum and product.</span> <span class="kd">example</span><span class="w"> </span><span class="o">[</span><span class="n">Fintype</span><span class="w"> </span><span class="n">ι</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="bp">⨁</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="bp">≃ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="bp">Π</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">linearEquivFunOnFintype</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="n">V</span> <span class="kd">example</span> <span class="o">[</span><span class="n">Fintype</span> <span class="n">ι</span><span class="o">]</span> <span class="o">:</span> <span class="o">(</span><span class="bp">⨁</span> <span class="n">i</span><span class="o">,</span> <span class="n">V</span> <span class="n">i</span><span class="o">)</span> <span class="bp">≃ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="o">(</span><span class="bp">Π</span> <span class="n">i</span><span class="o">,</span> <span class="n">V</span> <span class="n">i</span><span class="o">)</span> <span class="o">:=</span> <span class="n">linearEquivFunOnFintype</span> <span class="n">K</span> <span class="n">ι</span> <span class="n">V</span> <span class="kd">end</span><span class="w"> </span><span class="n">families</span> <span class="kd">end</span> <span class="n">families</span> </pre></div> </div> </section> </section> <section id="subspaces-and-quotients"> <span id="index-2"></span><h2><span class="section-number">9.2. </span>Subspaces and quotients<a class="headerlink" href="#subspaces-and-quotients" title="Link to this heading"></a></h2> <span id="index-2"></span><h2><span class="section-number">9.2. </span>Subspaces and quotients<a class="headerlink" href="#subspaces-and-quotients" title="Permalink to this heading"></a></h2> <section id="subspaces"> <h3><span class="section-number">9.2.1. </span>Subspaces<a class="headerlink" href="#subspaces" title="Link to this heading"></a></h3> <h3><span class="section-number">9.2.1. </span>Subspaces<a class="headerlink" href="#subspaces" title="Permalink to this heading"></a></h3> <p>Just as linear maps are bundled, a linear subspace of <code class="docutils literal notranslate"><span class="pre">V</span></code> is also a bundled structure consisting of a set in <code class="docutils literal notranslate"><span class="pre">V</span></code>, called the carrier of the subspace, with the relevant closure properties. Again the word module appears instead of vector space because of the more general context that Mathlib actually uses for linear algebra.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">K</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Field</span><span class="w"> </span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">V</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">AddCommGroup</span><span class="w"> </span><span class="n">V</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Module</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">K</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Field</span> <span class="n">K</span><span class="o">]</span> <span class="o">{</span><span class="n">V</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">AddCommGroup</span> <span class="n">V</span><span class="o">]</span> <span class="o">[</span><span class="n">Module</span> <span class="n">K</span> <span class="n">V</span><span class="o">]</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">U</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hx</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">U</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hy</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">U</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">U</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">U.add_mem</span><span class="w"> </span><span class="n">hx</span><span class="w"> </span><span class="n">hy</span> <span class="kd">example</span> <span class="o">(</span><span class="n">U</span> <span class="o">:</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">{</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">V</span><span class="o">}</span> <span class="o">(</span><span class="n">hx</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">U</span><span class="o">)</span> <span class="o">(</span><span class="n">hy</span> <span class="o">:</span> <span class="n">y</span> <span class="bp">∈</span> <span class="n">U</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">y</span> <span class="bp">∈</span> <span class="n">U</span> <span class="o">:=</span> <span class="n">U.add_mem</span> <span class="n">hx</span> <span class="n">hy</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">U</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hx</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">U</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">K</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">U</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">U.smul_mem</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">hx</span> <span class="kd">example</span> <span class="o">(</span><span class="n">U</span> <span class="o">:</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">{</span><span class="n">x</span> <span class="o">:</span> <span class="n">V</span><span class="o">}</span> <span class="o">(</span><span class="n">hx</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">U</span><span class="o">)</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">K</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">•</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">U</span> <span class="o">:=</span> <span class="n">U.smul_mem</span> <span class="n">a</span> <span class="n">hx</span> </pre></div> </div> <p>In the example above, it is important to understand that <code class="docutils literal notranslate"><span class="pre">Submodule</span> <span class="pre">K</span> <span class="pre">V</span></code> is the type of <code class="docutils literal notranslate"><span class="pre">K</span></code>-linear
-
@@ -396,19 +392,19 @@ equal in the same way it is used to prove that two sets are equal.</p><p>To state and prove, for example, that <code class="docutils literal notranslate"><span class="pre">ℝ</span></code> is a <code class="docutils literal notranslate"><span class="pre">ℝ</span></code>-linear subspace of <code class="docutils literal notranslate"><span class="pre">ℂ</span></code>, what we really want is to construct a term of type <code class="docutils literal notranslate"><span class="pre">Submodule</span> <span class="pre">ℝ</span> <span class="pre">ℂ</span></code> whose projection to <code class="docutils literal notranslate"><span class="pre">Set</span> <span class="pre">ℂ</span></code> is <code class="docutils literal notranslate"><span class="pre">ℝ</span></code>, or, more precisely, the image of <code class="docutils literal notranslate"><span class="pre">ℝ</span></code> in <code class="docutils literal notranslate"><span class="pre">ℂ</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">noncomputable</span><span class="w"> </span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="n">ℂ</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">carrier</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Set.range</span><span class="w"> </span><span class="o">((</span><span class="bp">↑</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℂ</span><span class="o">)</span> <span class="w"> </span><span class="n">add_mem'</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rintro</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="o">⟨</span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="n">rfl</span><span class="o">⟩</span><span class="w"> </span><span class="o">⟨</span><span class="n">m</span><span class="o">,</span><span class="w"> </span><span class="n">rfl</span><span class="o">⟩</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">m</span> <span class="w"> </span><span class="n">simp</span> <span class="w"> </span><span class="n">zero_mem'</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="mi">0</span> <span class="w"> </span><span class="n">simp</span> <span class="w"> </span><span class="n">smul_mem'</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rintro</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="o">⟨</span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="n">rfl</span><span class="o">⟩</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">c</span><span class="bp">*</span><span class="n">a</span> <span class="w"> </span><span class="n">simp</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">noncomputable</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">Submodule</span> <span class="n">ℝ</span> <span class="n">ℂ</span> <span class="n">where</span> <span class="n">carrier</span> <span class="o">:=</span> <span class="n">Set.range</span> <span class="o">((</span><span class="bp">↑</span><span class="o">)</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">→</span> <span class="n">ℂ</span><span class="o">)</span> <span class="n">add_mem'</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rintro</span> <span class="n">_</span> <span class="n">_</span> <span class="o">⟨</span><span class="n">n</span><span class="o">,</span> <span class="n">rfl</span><span class="o">⟩</span> <span class="o">⟨</span><span class="n">m</span><span class="o">,</span> <span class="n">rfl</span><span class="o">⟩</span> <span class="n">use</span> <span class="n">n</span> <span class="bp">+</span> <span class="n">m</span> <span class="n">simp</span> <span class="n">zero_mem'</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">use</span> <span class="mi">0</span> <span class="n">simp</span> <span class="n">smul_mem'</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rintro</span> <span class="n">c</span> <span class="bp">-</span> <span class="o">⟨</span><span class="n">a</span><span class="o">,</span> <span class="n">rfl</span><span class="o">⟩</span> <span class="n">use</span> <span class="n">c</span><span class="bp">*</span><span class="n">a</span> <span class="n">simp</span> </pre></div> </div> <p>The prime at the end of proof fields in <code class="docutils literal notranslate"><span class="pre">Submodule</span></code> are analogous to the one in <code class="docutils literal notranslate"><span class="pre">LinearMap</span></code>.
-
@@ -420,32 +416,32 @@ a subspace by a linear map (of course we will see below that Mathlib already knoRemember that <code class="docutils literal notranslate"><span class="pre">Set.mem_preimage</span></code> can be used to rewrite a statement involving membership and preimage. This is the only lemma you will need in addition to the lemmas discussed above about <code class="docutils literal notranslate"><span class="pre">LinearMap</span></code> and <code class="docutils literal notranslate"><span class="pre">Submodule</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">preimage</span><span class="w"> </span><span class="o">{</span><span class="n">W</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">AddCommGroup</span><span class="w"> </span><span class="n">W</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Module</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">W</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">W</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">H</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">W</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">carrier</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="bp">⁻¹'</span><span class="w"> </span><span class="n">H</span> <span class="w"> </span><span class="n">zero_mem'</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">dsimp</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">add_mem'</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">smul_mem'</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">dsimp</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">preimage</span> <span class="o">{</span><span class="n">W</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">AddCommGroup</span> <span class="n">W</span><span class="o">]</span> <span class="o">[</span><span class="n">Module</span> <span class="n">K</span> <span class="n">W</span><span class="o">]</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="n">V</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">W</span><span class="o">)</span> <span class="o">(</span><span class="n">H</span> <span class="o">:</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="n">W</span><span class="o">)</span> <span class="o">:</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="n">V</span> <span class="n">where</span> <span class="n">carrier</span> <span class="o">:=</span> <span class="n">φ</span> <span class="bp">⁻¹'</span> <span class="n">H</span> <span class="n">zero_mem'</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">dsimp</span> <span class="gr">sorry</span> <span class="n">add_mem'</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="n">smul_mem'</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">dsimp</span> <span class="gr">sorry</span> </pre></div> </div> <p>Using type classes, Mathlib knows that a subspace of a vector space inherits a vector space structure.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">U</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Module</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">U</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">inferInstance</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">U</span> <span class="o">:</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">:</span> <span class="n">Module</span> <span class="n">K</span> <span class="n">U</span> <span class="o">:=</span> <span class="n">inferInstance</span> </pre></div> </div> <p>This example is subtle. The object <code class="docutils literal notranslate"><span class="pre">U</span></code> is not a type, but Lean automatically coerces it to a type by interpreting it as a subtype of <code class="docutils literal notranslate"><span class="pre">V</span></code>. So the above example can be restated more explicitly as:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">U</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Module</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">//</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">U</span><span class="o">}</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">inferInstance</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">U</span> <span class="o">:</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">:</span> <span class="n">Module</span> <span class="n">K</span> <span class="o">{</span><span class="n">x</span> <span class="o">:</span> <span class="n">V</span> <span class="bp">//</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">U</span><span class="o">}</span> <span class="o">:=</span> <span class="n">inferInstance</span> </pre></div> </div> </section> <section id="complete-lattice-structure-and-internal-direct-sums"> <h3><span class="section-number">9.2.2. </span>Complete lattice structure and internal direct sums<a class="headerlink" href="#complete-lattice-structure-and-internal-direct-sums" title="Link to this heading"></a></h3> <h3><span class="section-number">9.2.2. </span>Complete lattice structure and internal direct sums<a class="headerlink" href="#complete-lattice-structure-and-internal-direct-sums" title="Permalink to this heading"></a></h3> <p>An important benefit of having a type <code class="docutils literal notranslate"><span class="pre">Submodule</span> <span class="pre">K</span> <span class="pre">V</span></code> instead of a predicate <code class="docutils literal notranslate"><span class="pre">IsSubmodule</span> <span class="pre">:</span> <span class="pre">Set</span> <span class="pre">V</span> <span class="pre">→</span> <span class="pre">Prop</span></code> is that one can easily endow <code class="docutils literal notranslate"><span class="pre">Submodule</span> <span class="pre">K</span> <span class="pre">V</span></code> with additional structure. Importantly, it has the structure of a complete lattice structure with respect to
-
@@ -455,8 +451,8 @@ use the lattice operation <code class="docutils literal notranslate"><span classlemmas about lattices to the construction.</p> <p>Let us check that the set underlying the infimum of two subspaces is indeed, by definition, their intersection.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">H</span><span class="w"> </span><span class="n">H'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="o">((</span><span class="n">H</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">H'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">(</span><span class="n">H</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="o">(</span><span class="n">H'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">rfl</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">H</span> <span class="n">H'</span> <span class="o">:</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">:</span> <span class="o">((</span><span class="n">H</span> <span class="bp">⊓</span> <span class="n">H'</span> <span class="o">:</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">V</span><span class="o">)</span> <span class="bp">=</span> <span class="o">(</span><span class="n">H</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">V</span><span class="o">)</span> <span class="bp">∩</span> <span class="o">(</span><span class="n">H'</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">V</span><span class="o">)</span> <span class="o">:=</span> <span class="n">rfl</span> </pre></div> </div> <p>It may look strange to have a different notation for what amounts to the intersection of the
-
@@ -464,21 +460,21 @@ underlying sets, but the correspondence does not carry over to the supremum operunion, since a union of subspaces is not, in general, a subspace. Instead one needs to use the subspace generated by the union, which is done using <code class="docutils literal notranslate"><span class="pre">Submodule.span</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">H</span><span class="w"> </span><span class="n">H'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="o">((</span><span class="n">H</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">H'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">Submodule.span</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="o">((</span><span class="n">H</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="bp">∪</span><span class="w"> </span><span class="o">(</span><span class="n">H'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">V</span><span class="o">))</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">simp</span><span class="w"> </span><span class="o">[</span><span class="n">Submodule.span_union</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">H</span> <span class="n">H'</span> <span class="o">:</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">:</span> <span class="o">((</span><span class="n">H</span> <span class="bp">⊔</span> <span class="n">H'</span> <span class="o">:</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">V</span><span class="o">)</span> <span class="bp">=</span> <span class="n">Submodule.span</span> <span class="n">K</span> <span class="o">((</span><span class="n">H</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">V</span><span class="o">)</span> <span class="bp">∪</span> <span class="o">(</span><span class="n">H'</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">V</span><span class="o">))</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> <span class="o">[</span><span class="n">Submodule.span_union</span><span class="o">]</span> </pre></div> </div> <p>Another subtlety is that <code class="docutils literal notranslate"><span class="pre">V</span></code> itself does not have type <code class="docutils literal notranslate"><span class="pre">Submodule</span> <span class="pre">K</span> <span class="pre">V</span></code>, so we need a way to talk about <code class="docutils literal notranslate"><span class="pre">V</span></code> seen as a subspace of <code class="docutils literal notranslate"><span class="pre">V</span></code>. This is also provided by the lattice structure: the full subspace is the top element of this lattice.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="o">(</span><span class="bp">⊤</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">trivial</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">V</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">∈</span> <span class="o">(</span><span class="bp">⊤</span> <span class="o">:</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">:=</span> <span class="n">trivial</span> </pre></div> </div> <p>Similarly the bottom element of this lattice is the subspace whose only element is the zero element.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="o">(</span><span class="bp">⊥</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Submodule.mem_bot</span><span class="w"> </span><span class="n">K</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">V</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">∈</span> <span class="o">(</span><span class="bp">⊥</span> <span class="o">:</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="bp">↔</span> <span class="n">x</span> <span class="bp">=</span> <span class="mi">0</span> <span class="o">:=</span> <span class="n">Submodule.mem_bot</span> <span class="n">K</span> </pre></div> </div> <p>In particular we can discuss the case of subspaces that are in (internal) direct sum.
-
@@ -486,41 +482,41 @@ In the case of two subspaces, we use the general purpose predicate <code class="which makes sense for any bounded partially ordered type. In the case of general families of subspaces we use <code class="docutils literal notranslate"><span class="pre">DirectSum.IsInternal</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="c1">-- If two subspaces are in direct sum then they span the whole space.</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">U</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">IsCompl</span><span class="w"> </span><span class="n">U</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">U</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">⊤</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">h.sup_eq_top</span> <span class="kd">example</span> <span class="o">(</span><span class="n">U</span> <span class="n">V</span> <span class="o">:</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">IsCompl</span> <span class="n">U</span> <span class="n">V</span><span class="o">)</span> <span class="o">:</span> <span class="n">U</span> <span class="bp">⊔</span> <span class="n">V</span> <span class="bp">=</span> <span class="bp">⊤</span> <span class="o">:=</span> <span class="n">h.sup_eq_top</span> <span class="c1">-- If two subspaces are in direct sum then they intersect only at zero.</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">U</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">IsCompl</span><span class="w"> </span><span class="n">U</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">U</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">⊥</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">h.inf_eq_bot</span> <span class="kd">example</span> <span class="o">(</span><span class="n">U</span> <span class="n">V</span> <span class="o">:</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">IsCompl</span> <span class="n">U</span> <span class="n">V</span><span class="o">)</span> <span class="o">:</span> <span class="n">U</span> <span class="bp">⊓</span> <span class="n">V</span> <span class="bp">=</span> <span class="bp">⊥</span> <span class="o">:=</span> <span class="n">h.inf_eq_bot</span> <span class="kn">section</span> <span class="kn">open</span><span class="w"> </span><span class="n">DirectSum</span> <span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">ι</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">DecidableEq</span><span class="w"> </span><span class="n">ι</span><span class="o">]</span> <span class="kn">open</span> <span class="n">DirectSum</span> <span class="kd">variable</span> <span class="o">{</span><span class="n">ι</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">DecidableEq</span> <span class="n">ι</span><span class="o">]</span> <span class="c1">-- If subspaces are in direct sum then they span the whole space.</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">U</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">DirectSum.IsInternal</span><span class="w"> </span><span class="n">U</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="bp">⨆</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">U</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">⊤</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">h.submodule_iSup_eq_top</span> <span class="kd">example</span> <span class="o">(</span><span class="n">U</span> <span class="o">:</span> <span class="n">ι</span> <span class="bp">→</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">DirectSum.IsInternal</span> <span class="n">U</span><span class="o">)</span> <span class="o">:</span> <span class="bp">⨆</span> <span class="n">i</span><span class="o">,</span> <span class="n">U</span> <span class="n">i</span> <span class="bp">=</span> <span class="bp">⊤</span> <span class="o">:=</span> <span class="n">h.submodule_iSup_eq_top</span> <span class="c1">-- If subspaces are in direct sum then they pairwise intersect only at zero.</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">ι</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">DecidableEq</span><span class="w"> </span><span class="n">ι</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">U</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">DirectSum.IsInternal</span><span class="w"> </span><span class="n">U</span><span class="o">)</span> <span class="w"> </span><span class="o">{</span><span class="n">i</span><span class="w"> </span><span class="n">j</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hij</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="n">j</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">U</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">U</span><span class="w"> </span><span class="n">j</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">⊥</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">(</span><span class="n">h.submodule_independent.pairwiseDisjoint</span><span class="w"> </span><span class="n">hij</span><span class="o">)</span><span class="bp">.</span><span class="n">eq_bot</span> <span class="kd">example</span> <span class="o">{</span><span class="n">ι</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">DecidableEq</span> <span class="n">ι</span><span class="o">]</span> <span class="o">(</span><span class="n">U</span> <span class="o">:</span> <span class="n">ι</span> <span class="bp">→</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">DirectSum.IsInternal</span> <span class="n">U</span><span class="o">)</span> <span class="o">{</span><span class="n">i</span> <span class="n">j</span> <span class="o">:</span> <span class="n">ι</span><span class="o">}</span> <span class="o">(</span><span class="n">hij</span> <span class="o">:</span> <span class="n">i</span> <span class="bp">≠</span> <span class="n">j</span><span class="o">)</span> <span class="o">:</span> <span class="n">U</span> <span class="n">i</span> <span class="bp">⊓</span> <span class="n">U</span> <span class="n">j</span> <span class="bp">=</span> <span class="bp">⊥</span> <span class="o">:=</span> <span class="o">(</span><span class="n">h.submodule_independent.pairwiseDisjoint</span> <span class="n">hij</span><span class="o">)</span><span class="bp">.</span><span class="n">eq_bot</span> <span class="c1">-- Those conditions characterize direct sums.</span> <span class="k">#check</span><span class="w"> </span><span class="n">DirectSum.isInternal_submodule_iff_independent_and_iSup_eq_top</span> <span class="k">#check</span> <span class="n">DirectSum.isInternal_submodule_iff_independent_and_iSup_eq_top</span> <span class="c1">-- The relation with external direct sums: if a family of subspaces is</span> <span class="c1">-- in internal direct sum then the map from their external direct sum into `V`</span> <span class="c1">-- is a linear isomorphism.</span> <span class="kd">noncomputable</span><span class="w"> </span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">ι</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">DecidableEq</span><span class="w"> </span><span class="n">ι</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">U</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span> <span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">DirectSum.IsInternal</span><span class="w"> </span><span class="n">U</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="bp">⨁</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">U</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="bp">≃ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">LinearEquiv.ofBijective</span><span class="w"> </span><span class="o">(</span><span class="n">coeLinearMap</span><span class="w"> </span><span class="n">U</span><span class="o">)</span><span class="w"> </span><span class="n">h</span> <span class="kd">noncomputable</span> <span class="kd">example</span> <span class="o">{</span><span class="n">ι</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">DecidableEq</span> <span class="n">ι</span><span class="o">]</span> <span class="o">(</span><span class="n">U</span> <span class="o">:</span> <span class="n">ι</span> <span class="bp">→</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">DirectSum.IsInternal</span> <span class="n">U</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="bp">⨁</span> <span class="n">i</span><span class="o">,</span> <span class="n">U</span> <span class="n">i</span><span class="o">)</span> <span class="bp">≃ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">V</span> <span class="o">:=</span> <span class="n">LinearEquiv.ofBijective</span> <span class="o">(</span><span class="n">coeLinearMap</span> <span class="n">U</span><span class="o">)</span> <span class="n">h</span> <span class="kd">end</span> </pre></div> </div> </section> <section id="subspace-spanned-by-a-set"> <h3><span class="section-number">9.2.3. </span>Subspace spanned by a set<a class="headerlink" href="#subspace-spanned-by-a-set" title="Link to this heading"></a></h3> <h3><span class="section-number">9.2.3. </span>Subspace spanned by a set<a class="headerlink" href="#subspace-spanned-by-a-set" title="Permalink to this heading"></a></h3> <p>In addition to building subspaces out of existing subspaces, we can build them out of any set <code class="docutils literal notranslate"><span class="pre">s</span></code> using <code class="docutils literal notranslate"><span class="pre">Submodule.span</span> <span class="pre">K</span> <span class="pre">s</span></code> which builds the smallest subspace containing <code class="docutils literal notranslate"><span class="pre">s</span></code>.
-
@@ -528,11 +524,11 @@ On paper it is common to use that this space is made of all linear combinations<code class="docutils literal notranslate"><span class="pre">s</span></code>. But it is often more efficient to use its universal property expressed by <code class="docutils literal notranslate"><span class="pre">Submodule.span_le</span></code>, and the whole theory of Galois connections.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">V</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">E</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submodule.span</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Submodule.span_le</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">s</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">V</span><span class="o">}</span> <span class="o">(</span><span class="n">E</span> <span class="o">:</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">:</span> <span class="n">Submodule.span</span> <span class="n">K</span> <span class="n">s</span> <span class="bp">≤</span> <span class="n">E</span> <span class="bp">↔</span> <span class="n">s</span> <span class="bp">⊆</span> <span class="n">E</span> <span class="o">:=</span> <span class="n">Submodule.span_le</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">GaloisInsertion</span><span class="w"> </span><span class="o">(</span><span class="n">Submodule.span</span><span class="w"> </span><span class="n">K</span><span class="o">)</span><span class="w"> </span><span class="o">((</span><span class="bp">↑</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Submodule.gi</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">GaloisInsertion</span> <span class="o">(</span><span class="n">Submodule.span</span> <span class="n">K</span><span class="o">)</span> <span class="o">((</span><span class="bp">↑</span><span class="o">)</span> <span class="o">:</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="n">V</span> <span class="bp">→</span> <span class="n">Set</span> <span class="n">V</span><span class="o">)</span> <span class="o">:=</span> <span class="n">Submodule.gi</span> <span class="n">K</span> <span class="n">V</span> </pre></div> </div> <p>When those are not enough, one can use the relevant induction principle
-
@@ -542,35 +538,35 @@ sum and scalar multiplication.</p><p>As an exercise, let us reprove one implication of <code class="docutils literal notranslate"><span class="pre">Submodule.mem_sup</span></code>. Remember that you can use the <cite>module</cite> tactic to close goals that follow from the axioms relating the various algebraic operations on <code class="docutils literal notranslate"><span class="pre">V</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">S</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">T</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">S</span><span class="o">,</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">T</span><span class="o">,</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="bp">←</span><span class="w"> </span><span class="n">S.span_eq</span><span class="o">,</span><span class="w"> </span><span class="bp">←</span><span class="w"> </span><span class="n">T.span_eq</span><span class="o">,</span><span class="w"> </span><span class="bp">←</span><span class="w"> </span><span class="n">Submodule.span_union</span><span class="o">]</span><span class="w"> </span><span class="n">at</span><span class="w"> </span><span class="n">h</span> <span class="w"> </span><span class="n">induction</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="n">using</span><span class="w"> </span><span class="n">Submodule.span_induction</span><span class="w"> </span><span class="k">with</span> <span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">mem</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="bp">=></span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">zero</span><span class="w"> </span><span class="bp">=></span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">add</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">hx</span><span class="w"> </span><span class="n">hy</span><span class="w"> </span><span class="n">hx'</span><span class="w"> </span><span class="n">hy'</span><span class="w"> </span><span class="bp">=></span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">smul</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">hx</span><span class="w"> </span><span class="n">hx'</span><span class="w"> </span><span class="bp">=></span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">S</span> <span class="n">T</span> <span class="o">:</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="n">V</span><span class="o">}</span> <span class="o">{</span><span class="n">x</span> <span class="o">:</span> <span class="n">V</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">S</span> <span class="bp">⊔</span> <span class="n">T</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">s</span> <span class="bp">∈</span> <span class="n">S</span><span class="o">,</span> <span class="bp">∃</span> <span class="n">t</span> <span class="bp">∈</span> <span class="n">T</span><span class="o">,</span> <span class="n">x</span> <span class="bp">=</span> <span class="n">s</span> <span class="bp">+</span> <span class="n">t</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="bp">←</span> <span class="n">S.span_eq</span><span class="o">,</span> <span class="bp">←</span> <span class="n">T.span_eq</span><span class="o">,</span> <span class="bp">←</span> <span class="n">Submodule.span_union</span><span class="o">]</span> <span class="n">at</span> <span class="n">h</span> <span class="n">induction</span> <span class="n">h</span> <span class="n">using</span> <span class="n">Submodule.span_induction</span> <span class="k">with</span> <span class="bp">|</span> <span class="n">mem</span> <span class="n">y</span> <span class="n">h</span> <span class="bp">=></span> <span class="gr">sorry</span> <span class="bp">|</span> <span class="n">zero</span> <span class="bp">=></span> <span class="gr">sorry</span> <span class="bp">|</span> <span class="n">add</span> <span class="n">x</span> <span class="n">y</span> <span class="n">hx</span> <span class="n">hy</span> <span class="n">hx'</span> <span class="n">hy'</span> <span class="bp">=></span> <span class="gr">sorry</span> <span class="bp">|</span> <span class="n">smul</span> <span class="n">a</span> <span class="n">x</span> <span class="n">hx</span> <span class="n">hx'</span> <span class="bp">=></span> <span class="gr">sorry</span> </pre></div> </div> </section> <section id="pushing-and-pulling-subspaces"> <h3><span class="section-number">9.2.4. </span>Pushing and pulling subspaces<a class="headerlink" href="#pushing-and-pulling-subspaces" title="Link to this heading"></a></h3> <h3><span class="section-number">9.2.4. </span>Pushing and pulling subspaces<a class="headerlink" href="#pushing-and-pulling-subspaces" title="Permalink to this heading"></a></h3> <p>As promised earlier, we now describe how to push and pull subspaces by linear maps. As usual in Mathlib, the first operation is called <code class="docutils literal notranslate"><span class="pre">map</span></code> and the second one is called <code class="docutils literal notranslate"><span class="pre">comap</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">section</span> <span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">W</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">AddCommGroup</span><span class="w"> </span><span class="n">W</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Module</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">W</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">W</span><span class="o">)</span> <span class="kd">variable</span> <span class="o">{</span><span class="n">W</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">AddCommGroup</span> <span class="n">W</span><span class="o">]</span> <span class="o">[</span><span class="n">Module</span> <span class="n">K</span> <span class="n">W</span><span class="o">]</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="n">V</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">W</span><span class="o">)</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">E</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="k">in</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">Submodule.map</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">W</span><span class="o">)</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">E</span> <span class="o">:</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="k">in</span> <span class="k">#check</span> <span class="o">(</span><span class="n">Submodule.map</span> <span class="n">φ</span> <span class="n">E</span> <span class="o">:</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="n">W</span><span class="o">)</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">F</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">W</span><span class="o">)</span><span class="w"> </span><span class="k">in</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">Submodule.comap</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">F</span> <span class="o">:</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="n">W</span><span class="o">)</span> <span class="k">in</span> <span class="k">#check</span> <span class="o">(</span><span class="n">Submodule.comap</span> <span class="n">φ</span> <span class="n">F</span> <span class="o">:</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> </pre></div> </div> <p>Note those live in the <code class="docutils literal notranslate"><span class="pre">Submodule</span></code> namespace so one can use dot notation and write
-
@@ -578,9 +574,9 @@ As usual in Mathlib, the first operation is called <code class="docutils literalMathlib contributors use this spelling).</p> <p>In particular the range and kernel of a linear map are subspaces. Those special cases are important enough to get declarations.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">LinearMap.range</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">.</span><span class="n">map</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="bp">⊤</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">LinearMap.range_eq_map</span><span class="w"> </span><span class="n">φ</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">LinearMap.range</span> <span class="n">φ</span> <span class="bp">=</span> <span class="bp">.</span><span class="n">map</span> <span class="n">φ</span> <span class="bp">⊤</span> <span class="o">:=</span> <span class="n">LinearMap.range_eq_map</span> <span class="n">φ</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">LinearMap.ker</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">.</span><span class="n">comap</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="bp">⊥</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Submodule.comap_bot</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="c1">-- or `rfl`</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">LinearMap.ker</span> <span class="n">φ</span> <span class="bp">=</span> <span class="bp">.</span><span class="n">comap</span> <span class="n">φ</span> <span class="bp">⊥</span> <span class="o">:=</span> <span class="n">Submodule.comap_bot</span> <span class="n">φ</span> <span class="c1">-- or `rfl`</span> </pre></div> </div> <p>Note that we cannot write <code class="docutils literal notranslate"><span class="pre">φ.ker</span></code> instead of <code class="docutils literal notranslate"><span class="pre">LinearMap.ker</span> <span class="pre">φ</span></code> because <code class="docutils literal notranslate"><span class="pre">LinearMap.ker</span></code> also
-
@@ -590,109 +586,109 @@ However we were able to use the other flavor of dot notation in the right-hand sLean expects a term with type <code class="docutils literal notranslate"><span class="pre">Submodule</span> <span class="pre">K</span> <span class="pre">V</span></code> after elaborating the left-hand side, it interprets <code class="docutils literal notranslate"><span class="pre">.comap</span></code> as <code class="docutils literal notranslate"><span class="pre">Submodule.comap</span></code>.</p> <p>The following lemmas give the key relations between those submodule and the properties of <code class="docutils literal notranslate"><span class="pre">φ</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span><span class="w"> </span><span class="n">Function</span><span class="w"> </span><span class="n">LinearMap</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span> <span class="n">Function</span> <span class="n">LinearMap</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Injective</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">ker</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">⊥</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">ker_eq_bot.symm</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">Injective</span> <span class="n">φ</span> <span class="bp">↔</span> <span class="n">ker</span> <span class="n">φ</span> <span class="bp">=</span> <span class="bp">⊥</span> <span class="o">:=</span> <span class="n">ker_eq_bot.symm</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Surjective</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">range</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">⊤</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">range_eq_top.symm</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">Surjective</span> <span class="n">φ</span> <span class="bp">↔</span> <span class="n">range</span> <span class="n">φ</span> <span class="bp">=</span> <span class="bp">⊤</span> <span class="o">:=</span> <span class="n">range_eq_top.symm</span> </pre></div> </div> <p>As an exercise, let us prove the Galois connection property for <code class="docutils literal notranslate"><span class="pre">map</span></code> and <code class="docutils literal notranslate"><span class="pre">comap</span></code>. One can use the following lemmas but this is not required since they are true by definition.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="n">Submodule.mem_map_of_mem</span> <span class="k">#check</span><span class="w"> </span><span class="n">Submodule.mem_map</span> <span class="k">#check</span><span class="w"> </span><span class="n">Submodule.mem_comap</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="n">Submodule.mem_map_of_mem</span> <span class="k">#check</span> <span class="n">Submodule.mem_map</span> <span class="k">#check</span> <span class="n">Submodule.mem_comap</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">E</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">F</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">W</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">Submodule.map</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">Submodule.comap</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">E</span> <span class="o">:</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">(</span><span class="n">F</span> <span class="o">:</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="n">W</span><span class="o">)</span> <span class="o">:</span> <span class="n">Submodule.map</span> <span class="n">φ</span> <span class="n">E</span> <span class="bp">≤</span> <span class="n">F</span> <span class="bp">↔</span> <span class="n">E</span> <span class="bp">≤</span> <span class="n">Submodule.comap</span> <span class="n">φ</span> <span class="n">F</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> </section> <section id="quotient-spaces"> <h3><span class="section-number">9.2.5. </span>Quotient spaces<a class="headerlink" href="#quotient-spaces" title="Link to this heading"></a></h3> <h3><span class="section-number">9.2.5. </span>Quotient spaces<a class="headerlink" href="#quotient-spaces" title="Permalink to this heading"></a></h3> <p>Quotient vector spaces use the general quotient notation (typed with <code class="docutils literal notranslate"><span class="pre">\quot</span></code>, not the ordinary <code class="docutils literal notranslate"><span class="pre">/</span></code>). The projection onto a quotient space is <code class="docutils literal notranslate"><span class="pre">Submodule.mkQ</span></code> and the universal property is <code class="docutils literal notranslate"><span class="pre">Submodule.liftQ</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">E</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">(</span><span class="n">E</span> <span class="o">:</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Module</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="o">(</span><span class="n">V</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="n">E</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">inferInstance</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">Module</span> <span class="n">K</span> <span class="o">(</span><span class="n">V</span> <span class="bp">⧸</span> <span class="n">E</span><span class="o">)</span> <span class="o">:=</span> <span class="n">inferInstance</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">E.mkQ</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">V</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">V</span> <span class="bp">⧸</span> <span class="n">E</span> <span class="o">:=</span> <span class="n">E.mkQ</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ker</span><span class="w"> </span><span class="n">E.mkQ</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">E.ker_mkQ</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">ker</span> <span class="n">E.mkQ</span> <span class="bp">=</span> <span class="n">E</span> <span class="o">:=</span> <span class="n">E.ker_mkQ</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">range</span><span class="w"> </span><span class="n">E.mkQ</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">⊤</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">E.range_mkQ</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">range</span> <span class="n">E.mkQ</span> <span class="bp">=</span> <span class="bp">⊤</span> <span class="o">:=</span> <span class="n">E.range_mkQ</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">hφ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">ker</span><span class="w"> </span><span class="n">φ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">E.liftQ</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">hφ</span> <span class="kd">example</span> <span class="o">(</span><span class="n">hφ</span> <span class="o">:</span> <span class="n">E</span> <span class="bp">≤</span> <span class="n">ker</span> <span class="n">φ</span><span class="o">)</span> <span class="o">:</span> <span class="n">V</span> <span class="bp">⧸</span> <span class="n">E</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">W</span> <span class="o">:=</span> <span class="n">E.liftQ</span> <span class="n">φ</span> <span class="n">hφ</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">F</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">W</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hφ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="bp">.</span><span class="n">comap</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">F</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">W</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">E.mapQ</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">hφ</span> <span class="kd">example</span> <span class="o">(</span><span class="n">F</span> <span class="o">:</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="n">W</span><span class="o">)</span> <span class="o">(</span><span class="n">hφ</span> <span class="o">:</span> <span class="n">E</span> <span class="bp">≤</span> <span class="bp">.</span><span class="n">comap</span> <span class="n">φ</span> <span class="n">F</span><span class="o">)</span> <span class="o">:</span> <span class="n">V</span> <span class="bp">⧸</span> <span class="n">E</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">W</span> <span class="bp">⧸</span> <span class="n">F</span> <span class="o">:=</span> <span class="n">E.mapQ</span> <span class="n">F</span> <span class="n">φ</span> <span class="n">hφ</span> <span class="kd">noncomputable</span><span class="w"> </span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">V</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="n">LinearMap.ker</span><span class="w"> </span><span class="n">φ</span><span class="o">)</span><span class="w"> </span><span class="bp">≃ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">range</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">φ.quotKerEquivRange</span> <span class="kd">noncomputable</span> <span class="kd">example</span> <span class="o">:</span> <span class="o">(</span><span class="n">V</span> <span class="bp">⧸</span> <span class="n">LinearMap.ker</span> <span class="n">φ</span><span class="o">)</span> <span class="bp">≃ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">range</span> <span class="n">φ</span> <span class="o">:=</span> <span class="n">φ.quotKerEquivRange</span> </pre></div> </div> <p>As an exercise, let us prove the correspondence theorem for subspaces of quotient spaces. Mathlib knows a slightly more precise version as <code class="docutils literal notranslate"><span class="pre">Submodule.comapMkQRelIso</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span><span class="w"> </span><span class="n">Submodule</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span> <span class="n">Submodule</span> <span class="k">#check</span><span class="w"> </span><span class="n">Submodule.map_comap_eq</span> <span class="k">#check</span><span class="w"> </span><span class="n">Submodule.comap_map_eq</span> <span class="k">#check</span> <span class="n">Submodule.map_comap_eq</span> <span class="k">#check</span> <span class="n">Submodule.comap_map_eq</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="o">(</span><span class="n">V</span><span class="w"> </span><span class="bp">⧸</span><span class="w"> </span><span class="n">E</span><span class="o">)</span><span class="w"> </span><span class="bp">≃</span><span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">//</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="o">}</span><span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">toFun</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">invFun</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">left_inv</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">right_inv</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="o">(</span><span class="n">V</span> <span class="bp">⧸</span> <span class="n">E</span><span class="o">)</span> <span class="bp">≃</span> <span class="o">{</span> <span class="n">F</span> <span class="o">:</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="n">V</span> <span class="bp">//</span> <span class="n">E</span> <span class="bp">≤</span> <span class="n">F</span> <span class="o">}</span> <span class="n">where</span> <span class="n">toFun</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="n">invFun</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="n">left_inv</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="n">right_inv</span> <span class="o">:=</span> <span class="gr">sorry</span> </pre></div> </div> </section> </section> <section id="endomorphisms"> <h2><span class="section-number">9.3. </span>Endomorphisms<a class="headerlink" href="#endomorphisms" title="Link to this heading"></a></h2> <h2><span class="section-number">9.3. </span>Endomorphisms<a class="headerlink" href="#endomorphisms" title="Permalink to this heading"></a></h2> <p>An important special case of linear maps are endomorphisms: linear maps from a vector space to itself. They are interesting because they form a <code class="docutils literal notranslate"><span class="pre">K</span></code>-algebra. In particular we can evaluate polynomials with coefficients in <code class="docutils literal notranslate"><span class="pre">K</span></code> on them, and they can have eigenvalues and eigenvectors.</p> <p>Mathlib uses the abbreviation <code class="docutils literal notranslate"><span class="pre">Module.End</span> <span class="pre">K</span> <span class="pre">V</span> <span class="pre">:=</span> <span class="pre">V</span> <span class="pre">→ₗ[K]</span> <span class="pre">V</span></code> which is convenient when using a lot of these (especially after opening the <code class="docutils literal notranslate"><span class="pre">Module</span></code> namespace).</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">K</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Field</span><span class="w"> </span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">V</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">AddCommGroup</span><span class="w"> </span><span class="n">V</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Module</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">K</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Field</span> <span class="n">K</span><span class="o">]</span> <span class="o">{</span><span class="n">V</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">AddCommGroup</span> <span class="n">V</span><span class="o">]</span> <span class="o">[</span><span class="n">Module</span> <span class="n">K</span> <span class="n">V</span><span class="o">]</span> <span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">W</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">AddCommGroup</span><span class="w"> </span><span class="n">W</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Module</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">W</span><span class="o">]</span> <span class="kd">variable</span> <span class="o">{</span><span class="n">W</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">AddCommGroup</span> <span class="n">W</span><span class="o">]</span> <span class="o">[</span><span class="n">Module</span> <span class="n">K</span> <span class="n">W</span><span class="o">]</span> <span class="kn">open</span><span class="w"> </span><span class="n">Polynomial</span><span class="w"> </span><span class="n">Module</span><span class="w"> </span><span class="n">LinearMap</span> <span class="kn">open</span> <span class="n">Polynomial</span> <span class="n">Module</span> <span class="n">LinearMap</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="n">ψ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">End</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">ψ</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="bp">∘ₗ</span><span class="w"> </span><span class="n">ψ</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">LinearMap.mul_eq_comp</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">ψ</span><span class="w"> </span><span class="c1">-- `rfl` would also work</span> <span class="kd">example</span> <span class="o">(</span><span class="n">φ</span> <span class="n">ψ</span> <span class="o">:</span> <span class="n">End</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">:</span> <span class="n">φ</span> <span class="bp">*</span> <span class="n">ψ</span> <span class="bp">=</span> <span class="n">φ</span> <span class="bp">∘ₗ</span> <span class="n">ψ</span> <span class="o">:=</span> <span class="n">LinearMap.mul_eq_comp</span> <span class="n">φ</span> <span class="n">ψ</span> <span class="c1">-- `rfl` would also work</span> <span class="c1">-- evaluating `P` on `φ`</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">P</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">K</span><span class="o">[</span><span class="n">X</span><span class="o">])</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">End</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">aeval</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">P</span> <span class="kd">example</span> <span class="o">(</span><span class="n">P</span> <span class="o">:</span> <span class="n">K</span><span class="o">[</span><span class="n">X</span><span class="o">])</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="n">End</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">:</span> <span class="n">V</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">V</span> <span class="o">:=</span> <span class="n">aeval</span> <span class="n">φ</span> <span class="n">P</span> <span class="c1">-- evaluating `X` on `φ` gives back `φ`</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">End</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">aeval</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="o">(</span><span class="n">X</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">K</span><span class="o">[</span><span class="n">X</span><span class="o">])</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">aeval_X</span><span class="w"> </span><span class="n">φ</span> <span class="kd">example</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="n">End</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">:</span> <span class="n">aeval</span> <span class="n">φ</span> <span class="o">(</span><span class="n">X</span> <span class="o">:</span> <span class="n">K</span><span class="o">[</span><span class="n">X</span><span class="o">])</span> <span class="bp">=</span> <span class="n">φ</span> <span class="o">:=</span> <span class="n">aeval_X</span> <span class="n">φ</span> </pre></div> </div> <p>As an exercise manipulating endomorphisms, subspaces and polynomials, let us prove the (binary) kernels lemma: for any endomorphism <span class="math notranslate nohighlight">\(φ\)</span> and any two relatively prime polynomials <span class="math notranslate nohighlight">\(P\)</span> and <span class="math notranslate nohighlight">\(Q\)</span>, we have <span class="math notranslate nohighlight">\(\ker P(φ) ⊕ \ker Q(φ) = \ker \big(PQ(φ)\big)\)</span>.</p> <p>Note that <code class="docutils literal notranslate"><span class="pre">IsCoprime</span> <span class="pre">x</span> <span class="pre">y</span></code> is defined as <code class="docutils literal notranslate"><span class="pre">∃</span> <span class="pre">a</span> <span class="pre">b,</span> <span class="pre">a</span> <span class="pre">*</span> <span class="pre">x</span> <span class="pre">+</span> <span class="pre">b</span> <span class="pre">*</span> <span class="pre">y</span> <span class="pre">=</span> <span class="pre">1</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="n">Submodule.eq_bot_iff</span> <span class="k">#check</span><span class="w"> </span><span class="n">Submodule.mem_inf</span> <span class="k">#check</span><span class="w"> </span><span class="n">LinearMap.mem_ker</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="n">Submodule.eq_bot_iff</span> <span class="k">#check</span> <span class="n">Submodule.mem_inf</span> <span class="k">#check</span> <span class="n">LinearMap.mem_ker</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">P</span><span class="w"> </span><span class="n">Q</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">K</span><span class="o">[</span><span class="n">X</span><span class="o">])</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">IsCoprime</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="n">Q</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">End</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ker</span><span class="w"> </span><span class="o">(</span><span class="n">aeval</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">P</span><span class="o">)</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">ker</span><span class="w"> </span><span class="o">(</span><span class="n">aeval</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">Q</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">⊥</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">P</span> <span class="n">Q</span> <span class="o">:</span> <span class="n">K</span><span class="o">[</span><span class="n">X</span><span class="o">])</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">IsCoprime</span> <span class="n">P</span> <span class="n">Q</span><span class="o">)</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="n">End</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">:</span> <span class="n">ker</span> <span class="o">(</span><span class="n">aeval</span> <span class="n">φ</span> <span class="n">P</span><span class="o">)</span> <span class="bp">⊓</span> <span class="n">ker</span> <span class="o">(</span><span class="n">aeval</span> <span class="n">φ</span> <span class="n">Q</span><span class="o">)</span> <span class="bp">=</span> <span class="bp">⊥</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="k">#check</span><span class="w"> </span><span class="n">Submodule.add_mem_sup</span> <span class="k">#check</span><span class="w"> </span><span class="n">map_mul</span> <span class="k">#check</span><span class="w"> </span><span class="n">LinearMap.mul_apply</span> <span class="k">#check</span><span class="w"> </span><span class="n">LinearMap.ker_le_ker_comp</span> <span class="k">#check</span> <span class="n">Submodule.add_mem_sup</span> <span class="k">#check</span> <span class="n">map_mul</span> <span class="k">#check</span> <span class="n">LinearMap.mul_apply</span> <span class="k">#check</span> <span class="n">LinearMap.ker_le_ker_comp</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">P</span><span class="w"> </span><span class="n">Q</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">K</span><span class="o">[</span><span class="n">X</span><span class="o">])</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">IsCoprime</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="n">Q</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">End</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">ker</span><span class="w"> </span><span class="o">(</span><span class="n">aeval</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">P</span><span class="o">)</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">ker</span><span class="w"> </span><span class="o">(</span><span class="n">aeval</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">Q</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">ker</span><span class="w"> </span><span class="o">(</span><span class="n">aeval</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="o">(</span><span class="n">P</span><span class="bp">*</span><span class="n">Q</span><span class="o">))</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">P</span> <span class="n">Q</span> <span class="o">:</span> <span class="n">K</span><span class="o">[</span><span class="n">X</span><span class="o">])</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">IsCoprime</span> <span class="n">P</span> <span class="n">Q</span><span class="o">)</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="n">End</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">:</span> <span class="n">ker</span> <span class="o">(</span><span class="n">aeval</span> <span class="n">φ</span> <span class="n">P</span><span class="o">)</span> <span class="bp">⊔</span> <span class="n">ker</span> <span class="o">(</span><span class="n">aeval</span> <span class="n">φ</span> <span class="n">Q</span><span class="o">)</span> <span class="bp">=</span> <span class="n">ker</span> <span class="o">(</span><span class="n">aeval</span> <span class="n">φ</span> <span class="o">(</span><span class="n">P</span><span class="bp">*</span><span class="n">Q</span><span class="o">))</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>We now move to the discussions of eigenspaces and eigenvalues. The eigenspace
-
@@ -701,39 +697,39 @@ Eigenspaces are defined for all values of <code class="docutils literal notranslthey are interesting only when they are non-zero. However an eigenvector is, by definition, a non-zero element of an eigenspace. The corresponding predicate is <code class="docutils literal notranslate"><span class="pre">End.HasEigenvector</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">End</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">K</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">φ.eigenspace</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">LinearMap.ker</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">End.eigenspace_def</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="n">End</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">K</span><span class="o">)</span> <span class="o">:</span> <span class="n">φ.eigenspace</span> <span class="n">a</span> <span class="bp">=</span> <span class="n">LinearMap.ker</span> <span class="o">(</span><span class="n">φ</span> <span class="bp">-</span> <span class="n">a</span> <span class="bp">•</span> <span class="mi">1</span><span class="o">)</span> <span class="o">:=</span> <span class="n">End.eigenspace_def</span> </pre></div> </div> <p>Then there is a predicate <code class="docutils literal notranslate"><span class="pre">End.HasEigenvalue</span></code> and the corresponding subtype <code class="docutils literal notranslate"><span class="pre">End.Eigenvalues</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">End</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">K</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">φ.HasEigenvalue</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">φ.eigenspace</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≠</span><span class="w"> </span><span class="bp">⊥</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Iff.rfl</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="n">End</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">K</span><span class="o">)</span> <span class="o">:</span> <span class="n">φ.HasEigenvalue</span> <span class="n">a</span> <span class="bp">↔</span> <span class="n">φ.eigenspace</span> <span class="n">a</span> <span class="bp">≠</span> <span class="bp">⊥</span> <span class="o">:=</span> <span class="n">Iff.rfl</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">End</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">K</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">φ.HasEigenvalue</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">v</span><span class="o">,</span><span class="w"> </span><span class="n">φ.HasEigenvector</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">⟨</span><span class="n">End.HasEigenvalue.exists_hasEigenvector</span><span class="o">,</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="o">⟨</span><span class="n">_</span><span class="o">,</span><span class="w"> </span><span class="n">hv</span><span class="o">⟩</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">φ.hasEigenvalue_of_hasEigenvector</span><span class="w"> </span><span class="n">hv</span><span class="o">⟩</span> <span class="kd">example</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="n">End</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">K</span><span class="o">)</span> <span class="o">:</span> <span class="n">φ.HasEigenvalue</span> <span class="n">a</span> <span class="bp">↔</span> <span class="bp">∃</span> <span class="n">v</span><span class="o">,</span> <span class="n">φ.HasEigenvector</span> <span class="n">a</span> <span class="n">v</span> <span class="o">:=</span> <span class="o">⟨</span><span class="n">End.HasEigenvalue.exists_hasEigenvector</span><span class="o">,</span> <span class="k">fun</span> <span class="o">⟨</span><span class="n">_</span><span class="o">,</span> <span class="n">hv</span><span class="o">⟩</span> <span class="bp">↦</span> <span class="n">φ.hasEigenvalue_of_hasEigenvector</span> <span class="n">hv</span><span class="o">⟩</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">End</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">φ.Eigenvalues</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="bp">//</span><span class="w"> </span><span class="n">φ.HasEigenvalue</span><span class="w"> </span><span class="n">a</span><span class="o">}</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">example</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="n">End</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">:</span> <span class="n">φ.Eigenvalues</span> <span class="bp">=</span> <span class="o">{</span><span class="n">a</span> <span class="bp">//</span> <span class="n">φ.HasEigenvalue</span> <span class="n">a</span><span class="o">}</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="c1">-- Eigenvalue are roots of the minimal polynomial</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">End</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">K</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">φ.HasEigenvalue</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="o">(</span><span class="n">minpoly</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">φ</span><span class="o">)</span><span class="bp">.</span><span class="n">IsRoot</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">φ.isRoot_of_hasEigenvalue</span> <span class="kd">example</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="n">End</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">K</span><span class="o">)</span> <span class="o">:</span> <span class="n">φ.HasEigenvalue</span> <span class="n">a</span> <span class="bp">→</span> <span class="o">(</span><span class="n">minpoly</span> <span class="n">K</span> <span class="n">φ</span><span class="o">)</span><span class="bp">.</span><span class="n">IsRoot</span> <span class="n">a</span> <span class="o">:=</span> <span class="n">φ.isRoot_of_hasEigenvalue</span> <span class="c1">-- In finite dimension, the converse is also true (we will discuss dimension below)</span> <span class="kd">example</span><span class="w"> </span><span class="o">[</span><span class="n">FiniteDimensional</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">End</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">K</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">φ.HasEigenvalue</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="o">(</span><span class="n">minpoly</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">φ</span><span class="o">)</span><span class="bp">.</span><span class="n">IsRoot</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">φ.hasEigenvalue_iff_isRoot</span> <span class="kd">example</span> <span class="o">[</span><span class="n">FiniteDimensional</span> <span class="n">K</span> <span class="n">V</span><span class="o">]</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="n">End</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">K</span><span class="o">)</span> <span class="o">:</span> <span class="n">φ.HasEigenvalue</span> <span class="n">a</span> <span class="bp">↔</span> <span class="o">(</span><span class="n">minpoly</span> <span class="n">K</span> <span class="n">φ</span><span class="o">)</span><span class="bp">.</span><span class="n">IsRoot</span> <span class="n">a</span> <span class="o">:=</span> <span class="n">φ.hasEigenvalue_iff_isRoot</span> <span class="c1">-- Cayley-Hamilton</span> <span class="kd">example</span><span class="w"> </span><span class="o">[</span><span class="n">FiniteDimensional</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">End</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">aeval</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">φ.charpoly</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">φ.aeval_self_charpoly</span> <span class="kd">example</span> <span class="o">[</span><span class="n">FiniteDimensional</span> <span class="n">K</span> <span class="n">V</span><span class="o">]</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="n">End</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">:</span> <span class="n">aeval</span> <span class="n">φ</span> <span class="n">φ.charpoly</span> <span class="bp">=</span> <span class="mi">0</span> <span class="o">:=</span> <span class="n">φ.aeval_self_charpoly</span> </pre></div> </div> </section> <section id="matrices-bases-and-dimension"> <span id="matrices-bases-dimension"></span><h2><span class="section-number">9.4. </span>Matrices, bases and dimension<a class="headerlink" href="#matrices-bases-and-dimension" title="Link to this heading"></a></h2> <span id="matrices-bases-dimension"></span><h2><span class="section-number">9.4. </span>Matrices, bases and dimension<a class="headerlink" href="#matrices-bases-and-dimension" title="Permalink to this heading"></a></h2> <section id="matrices"> <span id="id2"></span><h3><span class="section-number">9.4.1. </span>Matrices<a class="headerlink" href="#matrices" title="Link to this heading"></a></h3> <span id="id2"></span><h3><span class="section-number">9.4.1. </span>Matrices<a class="headerlink" href="#matrices" title="Permalink to this heading"></a></h3> <p id="index-3">Before introducing bases for abstract vector spaces, we go back to the much more elementary setup of linear algebra in <span class="math notranslate nohighlight">\(K^n\)</span> for some field <span class="math notranslate nohighlight">\(K\)</span>. Here the main objects are vectors and matrices.
-
@@ -742,16 +738,16 @@ For concrete matrices we can use the <code class="docutils literal notranslate">and components of lines are separated by colons. When entries have a computable type such as <code class="docutils literal notranslate"><span class="pre">ℕ</span></code> or <code class="docutils literal notranslate"><span class="pre">ℚ</span></code>, we can use the <code class="docutils literal notranslate"><span class="pre">eval</span></code> command to play with basic operations.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">section</span><span class="w"> </span><span class="n">matrices</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">section</span> <span class="n">matrices</span> <span class="c1">-- Adding vectors</span> <span class="k">#eval</span><span class="w"> </span><span class="bp">!!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="mi">2</span><span class="o">]</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="bp">!!</span><span class="o">[</span><span class="mi">3</span><span class="o">,</span><span class="w"> </span><span class="mi">4</span><span class="o">]</span><span class="w"> </span><span class="c1">-- !![4, 6]</span> <span class="k">#eval</span> <span class="bp">!!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span> <span class="mi">2</span><span class="o">]</span> <span class="bp">+</span> <span class="bp">!!</span><span class="o">[</span><span class="mi">3</span><span class="o">,</span> <span class="mi">4</span><span class="o">]</span> <span class="c1">-- !![4, 6]</span> <span class="c1">-- Adding matrices</span> <span class="k">#eval</span><span class="w"> </span><span class="bp">!!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="mi">2</span><span class="bp">;</span><span class="w"> </span><span class="mi">3</span><span class="o">,</span><span class="w"> </span><span class="mi">4</span><span class="o">]</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="bp">!!</span><span class="o">[</span><span class="mi">3</span><span class="o">,</span><span class="w"> </span><span class="mi">4</span><span class="bp">;</span><span class="w"> </span><span class="mi">5</span><span class="o">,</span><span class="w"> </span><span class="mi">6</span><span class="o">]</span><span class="w"> </span><span class="c1">-- !![4, 6; 8, 10]</span> <span class="k">#eval</span> <span class="bp">!!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span> <span class="mi">2</span><span class="bp">;</span> <span class="mi">3</span><span class="o">,</span> <span class="mi">4</span><span class="o">]</span> <span class="bp">+</span> <span class="bp">!!</span><span class="o">[</span><span class="mi">3</span><span class="o">,</span> <span class="mi">4</span><span class="bp">;</span> <span class="mi">5</span><span class="o">,</span> <span class="mi">6</span><span class="o">]</span> <span class="c1">-- !![4, 6; 8, 10]</span> <span class="c1">-- Multiplying matrices</span> <span class="k">#eval</span><span class="w"> </span><span class="bp">!!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="mi">2</span><span class="bp">;</span><span class="w"> </span><span class="mi">3</span><span class="o">,</span><span class="w"> </span><span class="mi">4</span><span class="o">]</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="bp">!!</span><span class="o">[</span><span class="mi">3</span><span class="o">,</span><span class="w"> </span><span class="mi">4</span><span class="bp">;</span><span class="w"> </span><span class="mi">5</span><span class="o">,</span><span class="w"> </span><span class="mi">6</span><span class="o">]</span><span class="w"> </span><span class="c1">-- !![4, 6; 8, 10]</span> <span class="k">#eval</span> <span class="bp">!!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span> <span class="mi">2</span><span class="bp">;</span> <span class="mi">3</span><span class="o">,</span> <span class="mi">4</span><span class="o">]</span> <span class="bp">*</span> <span class="bp">!!</span><span class="o">[</span><span class="mi">3</span><span class="o">,</span> <span class="mi">4</span><span class="bp">;</span> <span class="mi">5</span><span class="o">,</span> <span class="mi">6</span><span class="o">]</span> <span class="c1">-- !![4, 6; 8, 10]</span> </pre></div> </div> <p>It is important to understand that this use of <code class="docutils literal notranslate"><span class="pre">#eval</span></code> is interesting only for
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@@ -766,16 +762,16 @@ from the left (resp. right) interprets the vector as a row (resp. column) vectorThis corresponds to operations <code class="docutils literal notranslate"><span class="pre">Matrix.vecMul</span></code>, with notation <code class="docutils literal notranslate"><span class="pre">ᵥ*</span></code> and <code class="docutils literal notranslate"><span class="pre">Matrix.mulVec</span></code>, with notation ` <cite>*ᵥ`</cite>. Those notations are scoped in the <code class="docutils literal notranslate"><span class="pre">Matrix</span></code> namespace that we therefore need to open.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span><span class="w"> </span><span class="n">Matrix</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span> <span class="n">Matrix</span> <span class="c1">-- matrices acting on vectors on the left</span> <span class="k">#eval</span><span class="w"> </span><span class="bp">!!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="mi">2</span><span class="bp">;</span><span class="w"> </span><span class="mi">3</span><span class="o">,</span><span class="w"> </span><span class="mi">4</span><span class="o">]</span><span class="w"> </span><span class="bp">*ᵥ</span><span class="w"> </span><span class="bp">!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="mi">1</span><span class="o">]</span><span class="w"> </span><span class="c1">-- ![3, 7]</span> <span class="k">#eval</span> <span class="bp">!!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span> <span class="mi">2</span><span class="bp">;</span> <span class="mi">3</span><span class="o">,</span> <span class="mi">4</span><span class="o">]</span> <span class="bp">*ᵥ</span> <span class="bp">!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span> <span class="mi">1</span><span class="o">]</span> <span class="c1">-- ![3, 7]</span> <span class="c1">-- matrices acting on vectors on the left, resulting in a size one matrix</span> <span class="k">#eval</span><span class="w"> </span><span class="bp">!!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="mi">2</span><span class="o">]</span><span class="w"> </span><span class="bp">*ᵥ</span><span class="w"> </span><span class="bp">!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="mi">1</span><span class="o">]</span><span class="w"> </span><span class="c1">-- ![3]</span> <span class="k">#eval</span> <span class="bp">!!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span> <span class="mi">2</span><span class="o">]</span> <span class="bp">*ᵥ</span> <span class="bp">!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span> <span class="mi">1</span><span class="o">]</span> <span class="c1">-- ![3]</span> <span class="c1">-- matrices acting on vectors on the right</span> <span class="k">#eval</span><span class="w"> </span><span class="bp">!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="mi">1</span><span class="o">]</span><span class="w"> </span><span class="bp">ᵥ*</span><span class="w"> </span><span class="bp">!!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="mi">2</span><span class="bp">;</span><span class="w"> </span><span class="mi">3</span><span class="o">,</span><span class="w"> </span><span class="mi">4</span><span class="bp">;</span><span class="w"> </span><span class="mi">5</span><span class="o">,</span><span class="w"> </span><span class="mi">6</span><span class="o">]</span><span class="w"> </span><span class="c1">-- ![9, 12]</span> <span class="k">#eval</span> <span class="bp">!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span> <span class="mi">1</span><span class="o">,</span> <span class="mi">1</span><span class="o">]</span> <span class="bp">ᵥ*</span> <span class="bp">!!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span> <span class="mi">2</span><span class="bp">;</span> <span class="mi">3</span><span class="o">,</span> <span class="mi">4</span><span class="bp">;</span> <span class="mi">5</span><span class="o">,</span> <span class="mi">6</span><span class="o">]</span> <span class="c1">-- ![9, 12]</span> </pre></div> </div> <p>In order to generate matrices with identical rows or columns specified by a vector, we
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@@ -783,24 +779,24 @@ use <code class="docutils literal notranslate"><span class="pre">Matrix.row</sparows or columns and the vector. For instance one can get single row or single column matrixes (more precisely matrices whose rows or columns are indexed by <code class="docutils literal notranslate"><span class="pre">Fin</span> <span class="pre">1</span></code>).</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#eval</span><span class="w"> </span><span class="n">row</span><span class="w"> </span><span class="o">(</span><span class="n">Fin</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="bp">!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="mi">2</span><span class="o">]</span><span class="w"> </span><span class="c1">-- !![1, 2]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#eval</span> <span class="n">row</span> <span class="o">(</span><span class="n">Fin</span> <span class="mi">1</span><span class="o">)</span> <span class="bp">!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span> <span class="mi">2</span><span class="o">]</span> <span class="c1">-- !![1, 2]</span> <span class="k">#eval</span><span class="w"> </span><span class="n">col</span><span class="w"> </span><span class="o">(</span><span class="n">Fin</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="bp">!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="mi">2</span><span class="o">]</span><span class="w"> </span><span class="c1">-- !![1; 2]</span> <span class="k">#eval</span> <span class="n">col</span> <span class="o">(</span><span class="n">Fin</span> <span class="mi">1</span><span class="o">)</span> <span class="bp">!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span> <span class="mi">2</span><span class="o">]</span> <span class="c1">-- !![1; 2]</span> </pre></div> </div> <p>Other familiar operations include the vector dot product, matrix transpose, and, for square matrices, determinant and trace.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="c1">-- vector dot product</span> <span class="k">#eval</span><span class="w"> </span><span class="bp">!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="mi">2</span><span class="o">]</span><span class="w"> </span><span class="bp">⬝ᵥ</span><span class="w"> </span><span class="bp">!</span><span class="o">[</span><span class="mi">3</span><span class="o">,</span><span class="w"> </span><span class="mi">4</span><span class="o">]</span><span class="w"> </span><span class="c1">-- `11`</span> <span class="k">#eval</span> <span class="bp">!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span> <span class="mi">2</span><span class="o">]</span> <span class="bp">⬝ᵥ</span> <span class="bp">!</span><span class="o">[</span><span class="mi">3</span><span class="o">,</span> <span class="mi">4</span><span class="o">]</span> <span class="c1">-- `11`</span> <span class="c1">-- matrix transpose</span> <span class="k">#eval</span><span class="w"> </span><span class="bp">!!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="mi">2</span><span class="bp">;</span><span class="w"> </span><span class="mi">3</span><span class="o">,</span><span class="w"> </span><span class="mi">4</span><span class="o">]</span><span class="bp">ᵀ</span><span class="w"> </span><span class="c1">-- `!![1, 3; 2, 4]`</span> <span class="k">#eval</span> <span class="bp">!!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span> <span class="mi">2</span><span class="bp">;</span> <span class="mi">3</span><span class="o">,</span> <span class="mi">4</span><span class="o">]</span><span class="bp">ᵀ</span> <span class="c1">-- `!![1, 3; 2, 4]`</span> <span class="c1">-- determinant</span> <span class="k">#eval</span><span class="w"> </span><span class="bp">!!</span><span class="o">[(</span><span class="mi">1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℤ</span><span class="o">),</span><span class="w"> </span><span class="mi">2</span><span class="bp">;</span><span class="w"> </span><span class="mi">3</span><span class="o">,</span><span class="w"> </span><span class="mi">4</span><span class="o">]</span><span class="bp">.</span><span class="n">det</span><span class="w"> </span><span class="c1">-- `-2`</span> <span class="k">#eval</span> <span class="bp">!!</span><span class="o">[(</span><span class="mi">1</span> <span class="o">:</span> <span class="n">ℤ</span><span class="o">),</span> <span class="mi">2</span><span class="bp">;</span> <span class="mi">3</span><span class="o">,</span> <span class="mi">4</span><span class="o">]</span><span class="bp">.</span><span class="n">det</span> <span class="c1">-- `-2`</span> <span class="c1">-- trace</span> <span class="k">#eval</span><span class="w"> </span><span class="bp">!!</span><span class="o">[(</span><span class="mi">1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℤ</span><span class="o">),</span><span class="w"> </span><span class="mi">2</span><span class="bp">;</span><span class="w"> </span><span class="mi">3</span><span class="o">,</span><span class="w"> </span><span class="mi">4</span><span class="o">]</span><span class="bp">.</span><span class="n">trace</span><span class="w"> </span><span class="c1">-- `5`</span> <span class="k">#eval</span> <span class="bp">!!</span><span class="o">[(</span><span class="mi">1</span> <span class="o">:</span> <span class="n">ℤ</span><span class="o">),</span> <span class="mi">2</span><span class="bp">;</span> <span class="mi">3</span><span class="o">,</span> <span class="mi">4</span><span class="o">]</span><span class="bp">.</span><span class="n">trace</span> <span class="c1">-- `5`</span> </pre></div> </div> <p>When entries do not have a computable type, for instance if they are real numbers, we cannot
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@@ -809,14 +805,14 @@ considerably expanding the trusted code base (i.e. the part of Lean that you neechecking proofs).</p> <p>So it is good to also use the <code class="docutils literal notranslate"><span class="pre">simp</span></code> and <code class="docutils literal notranslate"><span class="pre">norm_num</span></code> tactics in proofs, or their command counter-part for quick exploration.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="bp">#</span><span class="n">simp</span><span class="w"> </span><span class="bp">!!</span><span class="o">[(</span><span class="mi">1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">),</span><span class="w"> </span><span class="mi">2</span><span class="bp">;</span><span class="w"> </span><span class="mi">3</span><span class="o">,</span><span class="w"> </span><span class="mi">4</span><span class="o">]</span><span class="bp">.</span><span class="n">det</span><span class="w"> </span><span class="c1">-- `4 - 2*3`</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="bp">#</span><span class="n">simp</span> <span class="bp">!!</span><span class="o">[(</span><span class="mi">1</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">),</span> <span class="mi">2</span><span class="bp">;</span> <span class="mi">3</span><span class="o">,</span> <span class="mi">4</span><span class="o">]</span><span class="bp">.</span><span class="n">det</span> <span class="c1">-- `4 - 2*3`</span> <span class="bp">#</span><span class="n">norm_num</span><span class="w"> </span><span class="bp">!!</span><span class="o">[(</span><span class="mi">1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">),</span><span class="w"> </span><span class="mi">2</span><span class="bp">;</span><span class="w"> </span><span class="mi">3</span><span class="o">,</span><span class="w"> </span><span class="mi">4</span><span class="o">]</span><span class="bp">.</span><span class="n">det</span><span class="w"> </span><span class="c1">-- `-2`</span> <span class="bp">#</span><span class="n">norm_num</span> <span class="bp">!!</span><span class="o">[(</span><span class="mi">1</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">),</span> <span class="mi">2</span><span class="bp">;</span> <span class="mi">3</span><span class="o">,</span> <span class="mi">4</span><span class="o">]</span><span class="bp">.</span><span class="n">det</span> <span class="c1">-- `-2`</span> <span class="bp">#</span><span class="n">norm_num</span><span class="w"> </span><span class="bp">!!</span><span class="o">[(</span><span class="mi">1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">),</span><span class="w"> </span><span class="mi">2</span><span class="bp">;</span><span class="w"> </span><span class="mi">3</span><span class="o">,</span><span class="w"> </span><span class="mi">4</span><span class="o">]</span><span class="bp">.</span><span class="n">trace</span><span class="w"> </span><span class="c1">-- `5`</span> <span class="bp">#</span><span class="n">norm_num</span> <span class="bp">!!</span><span class="o">[(</span><span class="mi">1</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">),</span> <span class="mi">2</span><span class="bp">;</span> <span class="mi">3</span><span class="o">,</span> <span class="mi">4</span><span class="o">]</span><span class="bp">.</span><span class="n">trace</span> <span class="c1">-- `5`</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="n">d</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="k">in</span> <span class="bp">#</span><span class="n">simp</span><span class="w"> </span><span class="bp">!!</span><span class="o">[</span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="n">b</span><span class="bp">;</span><span class="w"> </span><span class="n">c</span><span class="o">,</span><span class="w"> </span><span class="n">d</span><span class="o">]</span><span class="bp">.</span><span class="n">det</span><span class="w"> </span><span class="c1">-- `a * d – b * c`</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="n">d</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="k">in</span> <span class="bp">#</span><span class="n">simp</span> <span class="bp">!!</span><span class="o">[</span><span class="n">a</span><span class="o">,</span> <span class="n">b</span><span class="bp">;</span> <span class="n">c</span><span class="o">,</span> <span class="n">d</span><span class="o">]</span><span class="bp">.</span><span class="n">det</span> <span class="c1">-- `a * d – b * c`</span> </pre></div> </div> <p>The next important operation on square matrices is inversion.
-
@@ -827,7 +823,7 @@ the zero matrix for non-invertible matrices.</p>and, for any matrix <code class="docutils literal notranslate"><span class="pre">A</span></code>, <code class="docutils literal notranslate"><span class="pre">A⁻¹</span></code> is defined as <code class="docutils literal notranslate"><span class="pre">Ring.inverse</span> <span class="pre">A.det</span> <span class="pre">•</span> <span class="pre">A.adjugate</span></code>. According to Cramer’s rule, this is indeed the inverse of <code class="docutils literal notranslate"><span class="pre">A</span></code> when the determinant of <code class="docutils literal notranslate"><span class="pre">A</span></code> is not zero.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="bp">#</span><span class="n">norm_num</span><span class="w"> </span><span class="o">[</span><span class="n">Matrix.inv_def</span><span class="o">]</span><span class="w"> </span><span class="bp">!!</span><span class="o">[(</span><span class="mi">1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">),</span><span class="w"> </span><span class="mi">2</span><span class="bp">;</span><span class="w"> </span><span class="mi">3</span><span class="o">,</span><span class="w"> </span><span class="mi">4</span><span class="o">]</span><span class="bp">⁻¹</span><span class="w"> </span><span class="c1">-- !![-2, 1; 3 / 2, -(1 / 2)]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="bp">#</span><span class="n">norm_num</span> <span class="o">[</span><span class="n">Matrix.inv_def</span><span class="o">]</span> <span class="bp">!!</span><span class="o">[(</span><span class="mi">1</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">),</span> <span class="mi">2</span><span class="bp">;</span> <span class="mi">3</span><span class="o">,</span> <span class="mi">4</span><span class="o">]</span><span class="bp">⁻¹</span> <span class="c1">-- !![-2, 1; 3 / 2, -(1 / 2)]</span> </pre></div> </div> <p>Of course this definition is really useful only for invertible matrices.
-
@@ -836,18 +832,18 @@ For instance, the <code class="docutils literal notranslate"><span class="pre">slemma which has an <code class="docutils literal notranslate"><span class="pre">Invertible</span></code> type-class assumption, so it will trigger only if this can be found by the type-class synthesis system. Here we make this fact available using a <code class="docutils literal notranslate"><span class="pre">have</span></code> statement.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">!!</span><span class="o">[(</span><span class="mi">1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">),</span><span class="w"> </span><span class="mi">2</span><span class="bp">;</span><span class="w"> </span><span class="mi">3</span><span class="o">,</span><span class="w"> </span><span class="mi">4</span><span class="o">]</span><span class="bp">⁻¹</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="bp">!!</span><span class="o">[(</span><span class="mi">1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">),</span><span class="w"> </span><span class="mi">2</span><span class="bp">;</span><span class="w"> </span><span class="mi">3</span><span class="o">,</span><span class="w"> </span><span class="mi">4</span><span class="o">]</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Invertible</span><span class="w"> </span><span class="bp">!!</span><span class="o">[(</span><span class="mi">1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">),</span><span class="w"> </span><span class="mi">2</span><span class="bp">;</span><span class="w"> </span><span class="mi">3</span><span class="o">,</span><span class="w"> </span><span class="mi">4</span><span class="o">]</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">Matrix.invertibleOfIsUnitDet</span> <span class="w"> </span><span class="n">norm_num</span> <span class="w"> </span><span class="n">simp</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="bp">!!</span><span class="o">[(</span><span class="mi">1</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">),</span> <span class="mi">2</span><span class="bp">;</span> <span class="mi">3</span><span class="o">,</span> <span class="mi">4</span><span class="o">]</span><span class="bp">⁻¹</span> <span class="bp">*</span> <span class="bp">!!</span><span class="o">[(</span><span class="mi">1</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">),</span> <span class="mi">2</span><span class="bp">;</span> <span class="mi">3</span><span class="o">,</span> <span class="mi">4</span><span class="o">]</span> <span class="bp">=</span> <span class="mi">1</span> <span class="o">:=</span> <span class="kd">by</span> <span class="k">have</span> <span class="o">:</span> <span class="n">Invertible</span> <span class="bp">!!</span><span class="o">[(</span><span class="mi">1</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">),</span> <span class="mi">2</span><span class="bp">;</span> <span class="mi">3</span><span class="o">,</span> <span class="mi">4</span><span class="o">]</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">apply</span> <span class="n">Matrix.invertibleOfIsUnitDet</span> <span class="n">norm_num</span> <span class="n">simp</span> </pre></div> </div> <p>In this fully concrete case, we could also use the <code class="docutils literal notranslate"><span class="pre">norm_num</span></code> machinery, and <code class="docutils literal notranslate"><span class="pre">apply?</span></code> to find the final line:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">!!</span><span class="o">[(</span><span class="mi">1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">),</span><span class="w"> </span><span class="mi">2</span><span class="bp">;</span><span class="w"> </span><span class="mi">3</span><span class="o">,</span><span class="w"> </span><span class="mi">4</span><span class="o">]</span><span class="bp">⁻¹</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="bp">!!</span><span class="o">[(</span><span class="mi">1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">),</span><span class="w"> </span><span class="mi">2</span><span class="bp">;</span><span class="w"> </span><span class="mi">3</span><span class="o">,</span><span class="w"> </span><span class="mi">4</span><span class="o">]</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">norm_num</span><span class="w"> </span><span class="o">[</span><span class="n">Matrix.inv_def</span><span class="o">]</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">one_fin_two.symm</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="bp">!!</span><span class="o">[(</span><span class="mi">1</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">),</span> <span class="mi">2</span><span class="bp">;</span> <span class="mi">3</span><span class="o">,</span> <span class="mi">4</span><span class="o">]</span><span class="bp">⁻¹</span> <span class="bp">*</span> <span class="bp">!!</span><span class="o">[(</span><span class="mi">1</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">),</span> <span class="mi">2</span><span class="bp">;</span> <span class="mi">3</span><span class="o">,</span> <span class="mi">4</span><span class="o">]</span> <span class="bp">=</span> <span class="mi">1</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">norm_num</span> <span class="o">[</span><span class="n">Matrix.inv_def</span><span class="o">]</span> <span class="n">exact</span> <span class="n">one_fin_two.symm</span> </pre></div> </div> <p>All the concrete matrices above have their rows and columns indexed by <code class="docutils literal notranslate"><span class="pre">Fin</span> <span class="pre">n</span></code> for
-
@@ -871,32 +867,32 @@ and accept the statement as meaningful, and then prove it by checking all entrieon <code class="docutils literal notranslate"><span class="pre">Fin</span> <span class="pre">2</span> <span class="pre">→</span> <span class="pre">Fin</span> <span class="pre">2</span> <span class="pre">→</span> <span class="pre">ℤ</span></code> but the matrix multiplication on <code class="docutils literal notranslate"><span class="pre">Matrix</span> <span class="pre">(Fin</span> <span class="pre">2)</span> <span class="pre">(Fin</span> <span class="pre">2)</span> <span class="pre">ℤ</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">section</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Fin</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Fin</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℤ</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">!!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="mi">1</span><span class="bp">;</span><span class="w"> </span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="mi">1</span><span class="o">]</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">ext</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="n">j</span> <span class="w"> </span><span class="n">fin_cases</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">fin_cases</span><span class="w"> </span><span class="n">j</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">rfl</span> <span class="kd">example</span> <span class="o">:</span> <span class="o">(</span><span class="k">fun</span> <span class="n">_</span> <span class="bp">↦</span> <span class="mi">1</span> <span class="o">:</span> <span class="n">Fin</span> <span class="mi">2</span> <span class="bp">→</span> <span class="n">Fin</span> <span class="mi">2</span> <span class="bp">→</span> <span class="n">ℤ</span><span class="o">)</span> <span class="bp">=</span> <span class="bp">!!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span> <span class="mi">1</span><span class="bp">;</span> <span class="mi">1</span><span class="o">,</span> <span class="mi">1</span><span class="o">]</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">ext</span> <span class="n">i</span> <span class="n">j</span> <span class="n">fin_cases</span> <span class="n">i</span> <span class="bp"><;></span> <span class="n">fin_cases</span> <span class="n">j</span> <span class="bp"><;></span> <span class="n">rfl</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Fin</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Fin</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℤ</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Fin</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Fin</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℤ</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">!!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="mi">1</span><span class="bp">;</span><span class="w"> </span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="mi">1</span><span class="o">]</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">ext</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="n">j</span> <span class="w"> </span><span class="n">fin_cases</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">fin_cases</span><span class="w"> </span><span class="n">j</span><span class="w"> </span><span class="bp"><;></span><span class="w"> </span><span class="n">rfl</span> <span class="kd">example</span> <span class="o">:</span> <span class="o">(</span><span class="k">fun</span> <span class="n">_</span> <span class="bp">↦</span> <span class="mi">1</span> <span class="o">:</span> <span class="n">Fin</span> <span class="mi">2</span> <span class="bp">→</span> <span class="n">Fin</span> <span class="mi">2</span> <span class="bp">→</span> <span class="n">ℤ</span><span class="o">)</span> <span class="bp">*</span> <span class="o">(</span><span class="k">fun</span> <span class="n">_</span> <span class="bp">↦</span> <span class="mi">1</span> <span class="o">:</span> <span class="n">Fin</span> <span class="mi">2</span> <span class="bp">→</span> <span class="n">Fin</span> <span class="mi">2</span> <span class="bp">→</span> <span class="n">ℤ</span><span class="o">)</span> <span class="bp">=</span> <span class="bp">!!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span> <span class="mi">1</span><span class="bp">;</span> <span class="mi">1</span><span class="o">,</span> <span class="mi">1</span><span class="o">]</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">ext</span> <span class="n">i</span> <span class="n">j</span> <span class="n">fin_cases</span> <span class="n">i</span> <span class="bp"><;></span> <span class="n">fin_cases</span> <span class="n">j</span> <span class="bp"><;></span> <span class="n">rfl</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">!!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="mi">1</span><span class="bp">;</span><span class="w"> </span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="mi">1</span><span class="o">]</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="bp">!!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="mi">1</span><span class="bp">;</span><span class="w"> </span><span class="mi">1</span><span class="o">,</span><span class="w"> </span><span class="mi">1</span><span class="o">]</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">!!</span><span class="o">[</span><span class="mi">2</span><span class="o">,</span><span class="w"> </span><span class="mi">2</span><span class="bp">;</span><span class="w"> </span><span class="mi">2</span><span class="o">,</span><span class="w"> </span><span class="mi">2</span><span class="o">]</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">norm_num</span> <span class="kd">example</span> <span class="o">:</span> <span class="bp">!!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span> <span class="mi">1</span><span class="bp">;</span> <span class="mi">1</span><span class="o">,</span> <span class="mi">1</span><span class="o">]</span> <span class="bp">*</span> <span class="bp">!!</span><span class="o">[</span><span class="mi">1</span><span class="o">,</span> <span class="mi">1</span><span class="bp">;</span> <span class="mi">1</span><span class="o">,</span> <span class="mi">1</span><span class="o">]</span> <span class="bp">=</span> <span class="bp">!!</span><span class="o">[</span><span class="mi">2</span><span class="o">,</span> <span class="mi">2</span><span class="bp">;</span> <span class="mi">2</span><span class="o">,</span> <span class="mi">2</span><span class="o">]</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">norm_num</span> </pre></div> </div> <p>In order to define matrices as functions without loosing the benefits of <code class="docutils literal notranslate"><span class="pre">Matrix</span></code> <p>In order to define matrices as functions without losing the benefits of <code class="docutils literal notranslate"><span class="pre">Matrix</span></code> for type class synthesis, we can use the equivalence <code class="docutils literal notranslate"><span class="pre">Matrix.of</span></code> between functions and matrices. This equivalence is secretly defined using <code class="docutils literal notranslate"><span class="pre">Equiv.refl</span></code>.</p> <p>For instance we can define Vandermonde matrices corresponding to a vector <code class="docutils literal notranslate"><span class="pre">v</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">v</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Fin</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">Matrix.vandermonde</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">Matrix.of</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="n">j</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Fin</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="o">(</span><span class="n">j</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">))</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">}</span> <span class="o">(</span><span class="n">v</span> <span class="o">:</span> <span class="n">Fin</span> <span class="n">n</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="n">Matrix.vandermonde</span> <span class="n">v</span> <span class="bp">=</span> <span class="n">Matrix.of</span> <span class="o">(</span><span class="k">fun</span> <span class="n">i</span> <span class="n">j</span> <span class="o">:</span> <span class="n">Fin</span> <span class="n">n</span> <span class="bp">↦</span> <span class="n">v</span> <span class="n">i</span> <span class="bp">^</span> <span class="o">(</span><span class="n">j</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">))</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="kd">end</span> <span class="kd">end</span><span class="w"> </span><span class="n">matrices</span> <span class="kd">end</span> <span class="n">matrices</span> </pre></div> </div> </section> <section id="bases"> <h3><span class="section-number">9.4.2. </span>Bases<a class="headerlink" href="#bases" title="Link to this heading"></a></h3> <h3><span class="section-number">9.4.2. </span>Bases<a class="headerlink" href="#bases" title="Permalink to this heading"></a></h3> <p>We now want to discuss bases of vector spaces. Informally there are many ways to define this notion. One can use a universal property. One can say a basis is a family of vectors that is linearly independent and spanning.
-
@@ -917,23 +913,23 @@ Evaluating such a function coming from a basis <code class="docutils literal not<code class="docutils literal notranslate"><span class="pre">i</span> <span class="pre">:</span> <span class="pre">ι</span></code> returns the component (or coordinate) of <code class="docutils literal notranslate"><span class="pre">v</span></code> on the <code class="docutils literal notranslate"><span class="pre">i</span></code>-th basis vector.</p> <p>The type of bases indexed by a type <code class="docutils literal notranslate"><span class="pre">ι</span></code> of <code class="docutils literal notranslate"><span class="pre">V</span></code> as a <code class="docutils literal notranslate"><span class="pre">K</span></code> vector space is <code class="docutils literal notranslate"><span class="pre">Basis</span> <span class="pre">ι</span> <span class="pre">K</span> <span class="pre">V</span></code>. The isomorphism is called <code class="docutils literal notranslate"><span class="pre">Basis.repr</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">K</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Field</span><span class="w"> </span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">V</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">AddCommGroup</span><span class="w"> </span><span class="n">V</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Module</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">K</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Field</span> <span class="n">K</span><span class="o">]</span> <span class="o">{</span><span class="n">V</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">AddCommGroup</span> <span class="n">V</span><span class="o">]</span> <span class="o">[</span><span class="n">Module</span> <span class="n">K</span> <span class="n">V</span><span class="o">]</span> <span class="kn">section</span> <span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">ι</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">B</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Basis</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">v</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">i</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="o">)</span> <span class="kd">variable</span> <span class="o">{</span><span class="n">ι</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">(</span><span class="n">B</span> <span class="o">:</span> <span class="n">Basis</span> <span class="n">ι</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">(</span><span class="n">v</span> <span class="o">:</span> <span class="n">V</span><span class="o">)</span> <span class="o">(</span><span class="n">i</span> <span class="o">:</span> <span class="n">ι</span><span class="o">)</span> <span class="c1">-- The basis vector with index ``i``</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">B</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">B</span> <span class="n">i</span> <span class="o">:</span> <span class="n">V</span><span class="o">)</span> <span class="c1">-- the linear isomorphism with the model space given by ``B``</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">B.repr</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">≃ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="bp">→₀</span><span class="w"> </span><span class="n">K</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">B.repr</span> <span class="o">:</span> <span class="n">V</span> <span class="bp">≃ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">ι</span> <span class="bp">→₀</span> <span class="n">K</span><span class="o">)</span> <span class="c1">-- the component function of ``v``</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">B.repr</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="bp">→₀</span><span class="w"> </span><span class="n">K</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">B.repr</span> <span class="n">v</span> <span class="o">:</span> <span class="n">ι</span> <span class="bp">→₀</span> <span class="n">K</span><span class="o">)</span> <span class="c1">-- the component of ``v`` with index ``i``</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">B.repr</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">K</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">B.repr</span> <span class="n">v</span> <span class="n">i</span> <span class="o">:</span> <span class="n">K</span><span class="o">)</span> </pre></div> </div> <p>Instead of starting with such an isomorphism, one can start with a family <code class="docutils literal notranslate"><span class="pre">b</span></code> of vectors that is
-
@@ -943,15 +939,15 @@ Here <code class="docutils literal notranslate"><span class="pre">⊤</span>This spelling looks a bit tortuous, but we will see below that it is almost equivalent by definition to the more readable <code class="docutils literal notranslate"><span class="pre">∀</span> <span class="pre">v,</span> <span class="pre">v</span> <span class="pre">∈</span> <span class="pre">Submodule.span</span> <span class="pre">K</span> <span class="pre">(Set.range</span> <span class="pre">b)</span></code> (the underscores in the snippet below refers to the useless information <code class="docutils literal notranslate"><span class="pre">v</span> <span class="pre">∈</span> <span class="pre">⊤</span></code>).</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">noncomputable</span><span class="w"> </span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">b_indep</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">LinearIndependent</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">b</span><span class="o">)</span> <span class="w"> </span><span class="o">(</span><span class="n">b_spans</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">v</span><span class="o">,</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">Submodule.span</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="o">(</span><span class="n">Set.range</span><span class="w"> </span><span class="n">b</span><span class="o">))</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Basis</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Basis.mk</span><span class="w"> </span><span class="n">b_indep</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">b_spans</span><span class="w"> </span><span class="n">v</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">noncomputable</span> <span class="kd">example</span> <span class="o">(</span><span class="n">b</span> <span class="o">:</span> <span class="n">ι</span> <span class="bp">→</span> <span class="n">V</span><span class="o">)</span> <span class="o">(</span><span class="n">b_indep</span> <span class="o">:</span> <span class="n">LinearIndependent</span> <span class="n">K</span> <span class="n">b</span><span class="o">)</span> <span class="o">(</span><span class="n">b_spans</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">v</span><span class="o">,</span> <span class="n">v</span> <span class="bp">∈</span> <span class="n">Submodule.span</span> <span class="n">K</span> <span class="o">(</span><span class="n">Set.range</span> <span class="n">b</span><span class="o">))</span> <span class="o">:</span> <span class="n">Basis</span> <span class="n">ι</span> <span class="n">K</span> <span class="n">V</span> <span class="o">:=</span> <span class="n">Basis.mk</span> <span class="n">b_indep</span> <span class="o">(</span><span class="k">fun</span> <span class="n">v</span> <span class="n">_</span> <span class="bp">↦</span> <span class="n">b_spans</span> <span class="n">v</span><span class="o">)</span> <span class="c1">-- The family of vectors underlying the above basis is indeed ``b``.</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">b_indep</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">LinearIndependent</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">b</span><span class="o">)</span> <span class="w"> </span><span class="o">(</span><span class="n">b_spans</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">v</span><span class="o">,</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">Submodule.span</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="o">(</span><span class="n">Set.range</span><span class="w"> </span><span class="n">b</span><span class="o">))</span><span class="w"> </span><span class="o">(</span><span class="n">i</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">Basis.mk</span><span class="w"> </span><span class="n">b_indep</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">b_spans</span><span class="w"> </span><span class="n">v</span><span class="o">)</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Basis.mk_apply</span><span class="w"> </span><span class="n">b_indep</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">b_spans</span><span class="w"> </span><span class="n">v</span><span class="o">)</span><span class="w"> </span><span class="n">i</span> <span class="kd">example</span> <span class="o">(</span><span class="n">b</span> <span class="o">:</span> <span class="n">ι</span> <span class="bp">→</span> <span class="n">V</span><span class="o">)</span> <span class="o">(</span><span class="n">b_indep</span> <span class="o">:</span> <span class="n">LinearIndependent</span> <span class="n">K</span> <span class="n">b</span><span class="o">)</span> <span class="o">(</span><span class="n">b_spans</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">v</span><span class="o">,</span> <span class="n">v</span> <span class="bp">∈</span> <span class="n">Submodule.span</span> <span class="n">K</span> <span class="o">(</span><span class="n">Set.range</span> <span class="n">b</span><span class="o">))</span> <span class="o">(</span><span class="n">i</span> <span class="o">:</span> <span class="n">ι</span><span class="o">)</span> <span class="o">:</span> <span class="n">Basis.mk</span> <span class="n">b_indep</span> <span class="o">(</span><span class="k">fun</span> <span class="n">v</span> <span class="n">_</span> <span class="bp">↦</span> <span class="n">b_spans</span> <span class="n">v</span><span class="o">)</span> <span class="n">i</span> <span class="bp">=</span> <span class="n">b</span> <span class="n">i</span> <span class="o">:=</span> <span class="n">Basis.mk_apply</span> <span class="n">b_indep</span> <span class="o">(</span><span class="k">fun</span> <span class="n">v</span> <span class="n">_</span> <span class="bp">↦</span> <span class="n">b_spans</span> <span class="n">v</span><span class="o">)</span> <span class="n">i</span> </pre></div> </div> <p>In particular the model vector space <code class="docutils literal notranslate"><span class="pre">ι</span> <span class="pre">→₀</span> <span class="pre">K</span></code> has a so-called canonical basis whose <code class="docutils literal notranslate"><span class="pre">repr</span></code>
-
@@ -961,27 +957,27 @@ function evaluated on any vector is the identity isomorphism. It is calledvanish expect for a single input value. More precisely the basis vector indexed by <code class="docutils literal notranslate"><span class="pre">i</span> <span class="pre">:</span> <span class="pre">ι</span></code> is <code class="docutils literal notranslate"><span class="pre">Finsupp.single</span> <span class="pre">i</span> <span class="pre">1</span></code> which is the finitely supported function taking value <code class="docutils literal notranslate"><span class="pre">1</span></code> at <code class="docutils literal notranslate"><span class="pre">i</span></code> and <code class="docutils literal notranslate"><span class="pre">0</span></code> everywhere else.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">[</span><span class="n">DecidableEq</span><span class="w"> </span><span class="n">ι</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">[</span><span class="n">DecidableEq</span> <span class="n">ι</span><span class="o">]</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Finsupp.basisSingleOne.repr</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">LinearEquiv.refl</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="o">(</span><span class="n">ι</span><span class="w"> </span><span class="bp">→₀</span><span class="w"> </span><span class="n">K</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">Finsupp.basisSingleOne.repr</span> <span class="bp">=</span> <span class="n">LinearEquiv.refl</span> <span class="n">K</span> <span class="o">(</span><span class="n">ι</span> <span class="bp">→₀</span> <span class="n">K</span><span class="o">)</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">i</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Finsupp.basisSingleOne</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">Finsupp.single</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">example</span> <span class="o">(</span><span class="n">i</span> <span class="o">:</span> <span class="n">ι</span><span class="o">)</span> <span class="o">:</span> <span class="n">Finsupp.basisSingleOne</span> <span class="n">i</span> <span class="bp">=</span> <span class="n">Finsupp.single</span> <span class="n">i</span> <span class="mi">1</span> <span class="o">:=</span> <span class="n">rfl</span> </pre></div> </div> <p>The story of finitely supported functions is unneeded when the indexing type is finite. In this case we can use the simpler <code class="docutils literal notranslate"><span class="pre">Pi.basisFun</span></code> which gives a basis of the whole <code class="docutils literal notranslate"><span class="pre">ι</span> <span class="pre">→</span> <span class="pre">K</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">[</span><span class="n">Finite</span><span class="w"> </span><span class="n">ι</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">K</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">i</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="k">Pi</span><span class="bp">.</span><span class="n">basisFun</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">ι</span><span class="o">)</span><span class="bp">.</span><span class="n">repr</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">simp</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">[</span><span class="n">Finite</span> <span class="n">ι</span><span class="o">]</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">ι</span> <span class="bp">→</span> <span class="n">K</span><span class="o">)</span> <span class="o">(</span><span class="n">i</span> <span class="o">:</span> <span class="n">ι</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="k">Pi</span><span class="bp">.</span><span class="n">basisFun</span> <span class="n">K</span> <span class="n">ι</span><span class="o">)</span><span class="bp">.</span><span class="n">repr</span> <span class="n">x</span> <span class="n">i</span> <span class="bp">=</span> <span class="n">x</span> <span class="n">i</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> </pre></div> </div> <p>Going back to the general case of bases of abstract vector spaces, we can express any vector as a linear combination of basis vectors. Let us first see the easy case of finite bases.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">[</span><span class="n">Fintype</span><span class="w"> </span><span class="n">ι</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∑</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="o">,</span><span class="w"> </span><span class="n">B.repr</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="o">(</span><span class="n">B</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">B.sum_repr</span><span class="w"> </span><span class="n">v</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">[</span><span class="n">Fintype</span> <span class="n">ι</span><span class="o">]</span> <span class="o">:</span> <span class="bp">∑</span> <span class="n">i</span> <span class="o">:</span> <span class="n">ι</span><span class="o">,</span> <span class="n">B.repr</span> <span class="n">v</span> <span class="n">i</span> <span class="bp">•</span> <span class="o">(</span><span class="n">B</span> <span class="n">i</span><span class="o">)</span> <span class="bp">=</span> <span class="n">v</span> <span class="o">:=</span> <span class="n">B.sum_repr</span> <span class="n">v</span> </pre></div> </div> <p>When <code class="docutils literal notranslate"><span class="pre">ι</span></code> is not finite, the above statement makes no sense a priori: we cannot take a sum over <code class="docutils literal notranslate"><span class="pre">ι</span></code>.
-
@@ -994,24 +990,24 @@ function <code class="docutils literal notranslate"><span class="pre">f</span></sum over the support of <code class="docutils literal notranslate"><span class="pre">c</span></code> of the scalar multiplication <code class="docutils literal notranslate"><span class="pre">c</span> <span class="pre">•</span> <span class="pre">f</span></code>. In particular, we can replace it by a sum over any finite set containing the support of <code class="docutils literal notranslate"><span class="pre">c</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="bp">→₀</span><span class="w"> </span><span class="n">K</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Finset</span><span class="w"> </span><span class="n">ι</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">c.support</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">s</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">Finsupp.linearCombination</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">∑</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Finsupp.linearCombination_apply_of_mem_supported</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">h</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">c</span> <span class="o">:</span> <span class="n">ι</span> <span class="bp">→₀</span> <span class="n">K</span><span class="o">)</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">ι</span> <span class="bp">→</span> <span class="n">V</span><span class="o">)</span> <span class="o">(</span><span class="n">s</span> <span class="o">:</span> <span class="n">Finset</span> <span class="n">ι</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">c.support</span> <span class="bp">⊆</span> <span class="n">s</span><span class="o">)</span> <span class="o">:</span> <span class="n">Finsupp.linearCombination</span> <span class="n">K</span> <span class="n">f</span> <span class="n">c</span> <span class="bp">=</span> <span class="bp">∑</span> <span class="n">i</span> <span class="bp">∈</span> <span class="n">s</span><span class="o">,</span> <span class="n">c</span> <span class="n">i</span> <span class="bp">•</span> <span class="n">f</span> <span class="n">i</span> <span class="o">:=</span> <span class="n">Finsupp.linearCombination_apply_of_mem_supported</span> <span class="n">K</span> <span class="n">h</span> </pre></div> </div> <p>One could also assume that <code class="docutils literal notranslate"><span class="pre">f</span></code> is finitely supported and still get a well defined sum. But the choice made by <code class="docutils literal notranslate"><span class="pre">Finsupp.linearCombination</span></code> is the one relevant to our basis discussion since it allows to state the generalization of <code class="docutils literal notranslate"><span class="pre">Basis.sum_repr</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Finsupp.linearCombination</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="o">(</span><span class="n">B.repr</span><span class="w"> </span><span class="n">v</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">B.linearCombination_repr</span><span class="w"> </span><span class="n">v</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">Finsupp.linearCombination</span> <span class="n">K</span> <span class="n">B</span> <span class="o">(</span><span class="n">B.repr</span> <span class="n">v</span><span class="o">)</span> <span class="bp">=</span> <span class="n">v</span> <span class="o">:=</span> <span class="n">B.linearCombination_repr</span> <span class="n">v</span> </pre></div> </div> <p>One could wonder why <code class="docutils literal notranslate"><span class="pre">K</span></code> is an explicit argument here, despite the fact it can be inferred from the type of <code class="docutils literal notranslate"><span class="pre">c</span></code>. The point is that the partially applied <code class="docutils literal notranslate"><span class="pre">Finsupp.linearCombination</span> <span class="pre">K</span> <span class="pre">f</span></code> is interesting in itself. It is not a bare function from <code class="docutils literal notranslate"><span class="pre">ι</span> <span class="pre">→₀</span> <span class="pre">K</span></code> to <code class="docutils literal notranslate"><span class="pre">V</span></code> but a <code class="docutils literal notranslate"><span class="pre">K</span></code>-linear map.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="k">in</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">Finsupp.linearCombination</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">ι</span><span class="w"> </span><span class="bp">→₀</span><span class="w"> </span><span class="n">K</span><span class="o">)</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">V</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">ι</span> <span class="bp">→</span> <span class="n">V</span><span class="o">)</span> <span class="k">in</span> <span class="k">#check</span> <span class="o">(</span><span class="n">Finsupp.linearCombination</span> <span class="n">K</span> <span class="n">f</span> <span class="o">:</span> <span class="o">(</span><span class="n">ι</span> <span class="bp">→₀</span> <span class="n">K</span><span class="o">)</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">V</span><span class="o">)</span> </pre></div> </div> <p>The above subtlety also explains why dot notation cannot be used to write
-
@@ -1031,41 +1027,41 @@ This isomorphism is characterized by the fact that it sends any function <code cto a linear map sending the basis vector <code class="docutils literal notranslate"><span class="pre">B</span> <span class="pre">i</span></code> to <code class="docutils literal notranslate"><span class="pre">u</span> <span class="pre">i</span></code>, for every <code class="docutils literal notranslate"><span class="pre">i</span> <span class="pre">:</span> <span class="pre">ι</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">section</span> <span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">W</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">AddCommGroup</span><span class="w"> </span><span class="n">W</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Module</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">W</span><span class="o">]</span> <span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">W</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">u</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">W</span><span class="o">)</span> <span class="kd">variable</span> <span class="o">{</span><span class="n">W</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">AddCommGroup</span> <span class="n">W</span><span class="o">]</span> <span class="o">[</span><span class="n">Module</span> <span class="n">K</span> <span class="n">W</span><span class="o">]</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="n">V</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">W</span><span class="o">)</span> <span class="o">(</span><span class="n">u</span> <span class="o">:</span> <span class="n">ι</span> <span class="bp">→</span> <span class="n">W</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">B.constr</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">ι</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">W</span><span class="o">)</span><span class="w"> </span><span class="bp">≃ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">V</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">W</span><span class="o">))</span> <span class="k">#check</span> <span class="o">(</span><span class="n">B.constr</span> <span class="n">K</span> <span class="o">:</span> <span class="o">(</span><span class="n">ι</span> <span class="bp">→</span> <span class="n">W</span><span class="o">)</span> <span class="bp">≃ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="o">(</span><span class="n">V</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">W</span><span class="o">))</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">B.constr</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">W</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">B.constr</span> <span class="n">K</span> <span class="n">u</span> <span class="o">:</span> <span class="n">V</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">W</span><span class="o">)</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">i</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">B.constr</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="o">(</span><span class="n">B</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">B.constr_basis</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="n">i</span> <span class="kd">example</span> <span class="o">(</span><span class="n">i</span> <span class="o">:</span> <span class="n">ι</span><span class="o">)</span> <span class="o">:</span> <span class="n">B.constr</span> <span class="n">K</span> <span class="n">u</span> <span class="o">(</span><span class="n">B</span> <span class="n">i</span><span class="o">)</span> <span class="bp">=</span> <span class="n">u</span> <span class="n">i</span> <span class="o">:=</span> <span class="n">B.constr_basis</span> <span class="n">K</span> <span class="n">u</span> <span class="n">i</span> </pre></div> </div> <p>This property is indeed characteristic because linear maps are determined by their values on bases:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="n">ψ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">W</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="o">(</span><span class="n">B</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">ψ</span><span class="w"> </span><span class="o">(</span><span class="n">B</span><span class="w"> </span><span class="n">i</span><span class="o">))</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">ψ</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">B.ext</span><span class="w"> </span><span class="n">h</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">φ</span> <span class="n">ψ</span> <span class="o">:</span> <span class="n">V</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">W</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">i</span><span class="o">,</span> <span class="n">φ</span> <span class="o">(</span><span class="n">B</span> <span class="n">i</span><span class="o">)</span> <span class="bp">=</span> <span class="n">ψ</span> <span class="o">(</span><span class="n">B</span> <span class="n">i</span><span class="o">))</span> <span class="o">:</span> <span class="n">φ</span> <span class="bp">=</span> <span class="n">ψ</span> <span class="o">:=</span> <span class="n">B.ext</span> <span class="n">h</span> </pre></div> </div> <p>If we also have a basis <code class="docutils literal notranslate"><span class="pre">B'</span></code> on the target space then we can identify linear maps with matrices. This identification is a <code class="docutils literal notranslate"><span class="pre">K</span></code>-linear isomorphism.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">ι'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">B'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Basis</span><span class="w"> </span><span class="n">ι'</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">W</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">Fintype</span><span class="w"> </span><span class="n">ι</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">DecidableEq</span><span class="w"> </span><span class="n">ι</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">Fintype</span><span class="w"> </span><span class="n">ι'</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">DecidableEq</span><span class="w"> </span><span class="n">ι'</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">ι'</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">(</span><span class="n">B'</span> <span class="o">:</span> <span class="n">Basis</span> <span class="n">ι'</span> <span class="n">K</span> <span class="n">W</span><span class="o">)</span> <span class="o">[</span><span class="n">Fintype</span> <span class="n">ι</span><span class="o">]</span> <span class="o">[</span><span class="n">DecidableEq</span> <span class="n">ι</span><span class="o">]</span> <span class="o">[</span><span class="n">Fintype</span> <span class="n">ι'</span><span class="o">]</span> <span class="o">[</span><span class="n">DecidableEq</span> <span class="n">ι'</span><span class="o">]</span> <span class="kn">open</span><span class="w"> </span><span class="n">LinearMap</span> <span class="kn">open</span> <span class="n">LinearMap</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">toMatrix</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="n">B'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">V</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">W</span><span class="o">)</span><span class="w"> </span><span class="bp">≃ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">Matrix</span><span class="w"> </span><span class="n">ι'</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="n">K</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">toMatrix</span> <span class="n">B</span> <span class="n">B'</span> <span class="o">:</span> <span class="o">(</span><span class="n">V</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">W</span><span class="o">)</span> <span class="bp">≃ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">Matrix</span> <span class="n">ι'</span> <span class="n">ι</span> <span class="n">K</span><span class="o">)</span> <span class="kn">open</span><span class="w"> </span><span class="n">Matrix</span><span class="w"> </span><span class="c1">-- get access to the ``*ᵥ`` notation for multiplication between matrices and vectors.</span> <span class="kn">open</span> <span class="n">Matrix</span> <span class="c1">-- get access to the ``*ᵥ`` notation for multiplication between matrices and vectors.</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">W</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">v</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">toMatrix</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="n">B'</span><span class="w"> </span><span class="n">φ</span><span class="o">)</span><span class="w"> </span><span class="bp">*ᵥ</span><span class="w"> </span><span class="o">(</span><span class="n">B.repr</span><span class="w"> </span><span class="n">v</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">B'.repr</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="n">v</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">toMatrix_mulVec_repr</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="n">B'</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">v</span> <span class="kd">example</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="n">V</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">W</span><span class="o">)</span> <span class="o">(</span><span class="n">v</span> <span class="o">:</span> <span class="n">V</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">toMatrix</span> <span class="n">B</span> <span class="n">B'</span> <span class="n">φ</span><span class="o">)</span> <span class="bp">*ᵥ</span> <span class="o">(</span><span class="n">B.repr</span> <span class="n">v</span><span class="o">)</span> <span class="bp">=</span> <span class="n">B'.repr</span> <span class="o">(</span><span class="n">φ</span> <span class="n">v</span><span class="o">)</span> <span class="o">:=</span> <span class="n">toMatrix_mulVec_repr</span> <span class="n">B</span> <span class="n">B'</span> <span class="n">φ</span> <span class="n">v</span> <span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">ι''</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">B''</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Basis</span><span class="w"> </span><span class="n">ι''</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">W</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">Fintype</span><span class="w"> </span><span class="n">ι''</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">DecidableEq</span><span class="w"> </span><span class="n">ι''</span><span class="o">]</span> <span class="kd">variable</span> <span class="o">{</span><span class="n">ι''</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">(</span><span class="n">B''</span> <span class="o">:</span> <span class="n">Basis</span> <span class="n">ι''</span> <span class="n">K</span> <span class="n">W</span><span class="o">)</span> <span class="o">[</span><span class="n">Fintype</span> <span class="n">ι''</span><span class="o">]</span> <span class="o">[</span><span class="n">DecidableEq</span> <span class="n">ι''</span><span class="o">]</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span><span class="w"> </span><span class="n">W</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">toMatrix</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="n">B''</span><span class="w"> </span><span class="n">φ</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">(</span><span class="n">toMatrix</span><span class="w"> </span><span class="n">B'</span><span class="w"> </span><span class="n">B''</span><span class="w"> </span><span class="bp">.</span><span class="n">id</span><span class="o">)</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="o">(</span><span class="n">toMatrix</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="n">B'</span><span class="w"> </span><span class="n">φ</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">simp</span> <span class="kd">example</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="n">V</span> <span class="bp">→ₗ</span><span class="o">[</span><span class="n">K</span><span class="o">]</span> <span class="n">W</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">toMatrix</span> <span class="n">B</span> <span class="n">B''</span> <span class="n">φ</span><span class="o">)</span> <span class="bp">=</span> <span class="o">(</span><span class="n">toMatrix</span> <span class="n">B'</span> <span class="n">B''</span> <span class="bp">.</span><span class="n">id</span><span class="o">)</span> <span class="bp">*</span> <span class="o">(</span><span class="n">toMatrix</span> <span class="n">B</span> <span class="n">B'</span> <span class="n">φ</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> <span class="kd">end</span> </pre></div>
-
@@ -1078,31 +1074,31 @@ This would then need to be complemented using that bases all have isomorphic indget the full result.</p> <p>Of course Mathlib already knows this, and <code class="docutils literal notranslate"><span class="pre">simp</span></code> can close the goal immediately, so you shouldn’t use it too soon, but rather use the provided lemmas.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span><span class="w"> </span><span class="n">Module</span><span class="w"> </span><span class="n">LinearMap</span><span class="w"> </span><span class="n">Matrix</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span> <span class="n">Module</span> <span class="n">LinearMap</span> <span class="n">Matrix</span> <span class="c1">-- Some lemmas coming from the fact that `LinearMap.toMatrix` is an algebra morphism.</span> <span class="k">#check</span><span class="w"> </span><span class="n">toMatrix_comp</span> <span class="k">#check</span><span class="w"> </span><span class="n">id_comp</span> <span class="k">#check</span><span class="w"> </span><span class="n">comp_id</span> <span class="k">#check</span><span class="w"> </span><span class="n">toMatrix_id</span> <span class="k">#check</span> <span class="n">toMatrix_comp</span> <span class="k">#check</span> <span class="n">id_comp</span> <span class="k">#check</span> <span class="n">comp_id</span> <span class="k">#check</span> <span class="n">toMatrix_id</span> <span class="c1">-- Some lemmas coming from the fact that ``Matrix.det`` is a multiplicative monoid morphism.</span> <span class="k">#check</span><span class="w"> </span><span class="n">Matrix.det_mul</span> <span class="k">#check</span><span class="w"> </span><span class="n">Matrix.det_one</span> <span class="kd">example</span><span class="w"> </span><span class="o">[</span><span class="n">Fintype</span><span class="w"> </span><span class="n">ι</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">B'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Basis</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">End</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="o">(</span><span class="n">toMatrix</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="n">φ</span><span class="o">)</span><span class="bp">.</span><span class="n">det</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">(</span><span class="n">toMatrix</span><span class="w"> </span><span class="n">B'</span><span class="w"> </span><span class="n">B'</span><span class="w"> </span><span class="n">φ</span><span class="o">)</span><span class="bp">.</span><span class="n">det</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">set</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">toMatrix</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="n">φ</span> <span class="w"> </span><span class="n">set</span><span class="w"> </span><span class="n">M'</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">toMatrix</span><span class="w"> </span><span class="n">B'</span><span class="w"> </span><span class="n">B'</span><span class="w"> </span><span class="n">φ</span> <span class="w"> </span><span class="n">set</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">(</span><span class="n">toMatrix</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="n">B'</span><span class="o">)</span><span class="w"> </span><span class="n">LinearMap.id</span> <span class="w"> </span><span class="n">set</span><span class="w"> </span><span class="n">P'</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">(</span><span class="n">toMatrix</span><span class="w"> </span><span class="n">B'</span><span class="w"> </span><span class="n">B</span><span class="o">)</span><span class="w"> </span><span class="n">LinearMap.id</span> <span class="w"> </span><span class="gr">sorry</span> <span class="k">#check</span> <span class="n">Matrix.det_mul</span> <span class="k">#check</span> <span class="n">Matrix.det_one</span> <span class="kd">example</span> <span class="o">[</span><span class="n">Fintype</span> <span class="n">ι</span><span class="o">]</span> <span class="o">(</span><span class="n">B'</span> <span class="o">:</span> <span class="n">Basis</span> <span class="n">ι</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">(</span><span class="n">φ</span> <span class="o">:</span> <span class="n">End</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="n">toMatrix</span> <span class="n">B</span> <span class="n">B</span> <span class="n">φ</span><span class="o">)</span><span class="bp">.</span><span class="n">det</span> <span class="bp">=</span> <span class="o">(</span><span class="n">toMatrix</span> <span class="n">B'</span> <span class="n">B'</span> <span class="n">φ</span><span class="o">)</span><span class="bp">.</span><span class="n">det</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">set</span> <span class="n">M</span> <span class="o">:=</span> <span class="n">toMatrix</span> <span class="n">B</span> <span class="n">B</span> <span class="n">φ</span> <span class="n">set</span> <span class="n">M'</span> <span class="o">:=</span> <span class="n">toMatrix</span> <span class="n">B'</span> <span class="n">B'</span> <span class="n">φ</span> <span class="n">set</span> <span class="n">P</span> <span class="o">:=</span> <span class="o">(</span><span class="n">toMatrix</span> <span class="n">B</span> <span class="n">B'</span><span class="o">)</span> <span class="n">LinearMap.id</span> <span class="n">set</span> <span class="n">P'</span> <span class="o">:=</span> <span class="o">(</span><span class="n">toMatrix</span> <span class="n">B'</span> <span class="n">B</span><span class="o">)</span> <span class="n">LinearMap.id</span> <span class="gr">sorry</span> <span class="kd">end</span> </pre></div> </div> </section> <section id="dimension"> <h3><span class="section-number">9.4.3. </span>Dimension<a class="headerlink" href="#dimension" title="Link to this heading"></a></h3> <h3><span class="section-number">9.4.3. </span>Dimension<a class="headerlink" href="#dimension" title="Permalink to this heading"></a></h3> <p>Returning to the case of a single vector space, bases are also useful to define the concept of dimension. Here again, there is the elementary case of finite-dimensional vector spaces.
-
@@ -1110,19 +1106,19 @@ For such spaces we expect a dimension which is a natural number.This is <code class="docutils literal notranslate"><span class="pre">Module.finrank</span></code>. It takes the base field as an explicit argument since a given abelian group can be a vector space over different fields.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">section</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">Module.finrank</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">Module.finrank</span> <span class="n">K</span> <span class="n">V</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="c1">-- `Fin n → K` is the archetypical space with dimension `n` over `K`.</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Module.finrank</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="o">(</span><span class="n">Fin</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">K</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Module.finrank_fin_fun</span><span class="w"> </span><span class="n">K</span> <span class="kd">example</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">:</span> <span class="n">Module.finrank</span> <span class="n">K</span> <span class="o">(</span><span class="n">Fin</span> <span class="n">n</span> <span class="bp">→</span> <span class="n">K</span><span class="o">)</span> <span class="bp">=</span> <span class="n">n</span> <span class="o">:=</span> <span class="n">Module.finrank_fin_fun</span> <span class="n">K</span> <span class="c1">-- Seen as a vector space over itself, `ℂ` has dimension one.</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Module.finrank</span><span class="w"> </span><span class="n">ℂ</span><span class="w"> </span><span class="n">ℂ</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Module.finrank_self</span><span class="w"> </span><span class="n">ℂ</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">Module.finrank</span> <span class="n">ℂ</span> <span class="n">ℂ</span> <span class="bp">=</span> <span class="mi">1</span> <span class="o">:=</span> <span class="n">Module.finrank_self</span> <span class="n">ℂ</span> <span class="c1">-- But as a real vector space it has dimension two.</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Module.finrank</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="n">ℂ</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Complex.finrank_real_complex</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">Module.finrank</span> <span class="n">ℝ</span> <span class="n">ℂ</span> <span class="bp">=</span> <span class="mi">2</span> <span class="o">:=</span> <span class="n">Complex.finrank_real_complex</span> </pre></div> </div> <p>Note that <code class="docutils literal notranslate"><span class="pre">Module.finrank</span></code> is defined for any vector space. It returns
-
@@ -1130,8 +1126,8 @@ zero for infinite dimensional vector spaces, just as division by zero returns ze<p>Of course many lemmas require a finite dimension assumption. This is the role of the <code class="docutils literal notranslate"><span class="pre">FiniteDimensional</span></code> typeclass. For instance, think about how the next example fails without this assumption.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">[</span><span class="n">FiniteDimensional</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">Module.finrank</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">Nontrivial</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Module.finrank_pos_iff</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">[</span><span class="n">FiniteDimensional</span> <span class="n">K</span> <span class="n">V</span><span class="o">]</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp"><</span> <span class="n">Module.finrank</span> <span class="n">K</span> <span class="n">V</span> <span class="bp">↔</span> <span class="n">Nontrivial</span> <span class="n">V</span> <span class="o">:=</span> <span class="n">Module.finrank_pos_iff</span> </pre></div> </div> <p>In the above statement, <code class="docutils literal notranslate"><span class="pre">Nontrivial</span> <span class="pre">V</span></code> means <code class="docutils literal notranslate"><span class="pre">V</span></code> has at least two different elements.
-
@@ -1140,44 +1136,44 @@ This is fine when using it from left to right, but not when using it from rightbecause Lean has no way to guess <code class="docutils literal notranslate"><span class="pre">K</span></code> from the statement <code class="docutils literal notranslate"><span class="pre">Nontrivial</span> <span class="pre">V</span></code>. In that case it is useful to use the name argument syntax, after checking that the lemma is stated over a ring named <code class="docutils literal notranslate"><span class="pre">R</span></code>. So we can write:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">[</span><span class="n">FiniteDimensional</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">Module.finrank</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Nontrivial</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="o">(</span><span class="n">Module.finrank_pos_iff</span><span class="w"> </span><span class="o">(</span><span class="n">R</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">K</span><span class="o">))</span><span class="bp">.</span><span class="mi">1</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">h</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">[</span><span class="n">FiniteDimensional</span> <span class="n">K</span> <span class="n">V</span><span class="o">]</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp"><</span> <span class="n">Module.finrank</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">:</span> <span class="n">Nontrivial</span> <span class="n">V</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">apply</span> <span class="o">(</span><span class="n">Module.finrank_pos_iff</span> <span class="o">(</span><span class="n">R</span> <span class="o">:=</span> <span class="n">K</span><span class="o">))</span><span class="bp">.</span><span class="mi">1</span> <span class="n">exact</span> <span class="n">h</span> </pre></div> </div> <p>The above spelling is strange because we already have <code class="docutils literal notranslate"><span class="pre">h</span></code> as an assumption, so we could just as well give the full proof <code class="docutils literal notranslate"><span class="pre">Module.finrank_pos_iff.1</span> <span class="pre">h</span></code> but it is good to know for more complicated cases.</p> <p>By definition, <code class="docutils literal notranslate"><span class="pre">FiniteDimensional</span> <span class="pre">K</span> <span class="pre">V</span></code> can be read from any basis.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">ι</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">B</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Basis</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">ι</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">(</span><span class="n">B</span> <span class="o">:</span> <span class="n">Basis</span> <span class="n">ι</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="kd">example</span><span class="w"> </span><span class="o">[</span><span class="n">Finite</span><span class="w"> </span><span class="n">ι</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">FiniteDimensional</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">FiniteDimensional.of_fintype_basis</span><span class="w"> </span><span class="n">B</span> <span class="kd">example</span> <span class="o">[</span><span class="n">Finite</span> <span class="n">ι</span><span class="o">]</span> <span class="o">:</span> <span class="n">FiniteDimensional</span> <span class="n">K</span> <span class="n">V</span> <span class="o">:=</span> <span class="n">FiniteDimensional.of_fintype_basis</span> <span class="n">B</span> <span class="kd">example</span><span class="w"> </span><span class="o">[</span><span class="n">FiniteDimensional</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Finite</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">(</span><span class="n">FiniteDimensional.fintypeBasisIndex</span><span class="w"> </span><span class="n">B</span><span class="o">)</span><span class="bp">.</span><span class="n">finite</span> <span class="kd">example</span> <span class="o">[</span><span class="n">FiniteDimensional</span> <span class="n">K</span> <span class="n">V</span><span class="o">]</span> <span class="o">:</span> <span class="n">Finite</span> <span class="n">ι</span> <span class="o">:=</span> <span class="o">(</span><span class="n">FiniteDimensional.fintypeBasisIndex</span> <span class="n">B</span><span class="o">)</span><span class="bp">.</span><span class="n">finite</span> <span class="kd">end</span> </pre></div> </div> <p>Using that the subtype corresponding to a linear subspace has a vector space structure, we can talk about the dimension of a subspace.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">section</span> <span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">E</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">FiniteDimensional</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">]</span> <span class="kd">variable</span> <span class="o">(</span><span class="n">E</span> <span class="n">F</span> <span class="o">:</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">[</span><span class="n">FiniteDimensional</span> <span class="n">K</span> <span class="n">V</span><span class="o">]</span> <span class="kn">open</span><span class="w"> </span><span class="n">Module</span> <span class="kn">open</span> <span class="n">Module</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">finrank</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="o">(</span><span class="n">E</span><span class="w"> </span><span class="bp">⊔</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">finrank</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="o">(</span><span class="n">E</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span> <span class="w"> </span><span class="n">finrank</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">finrank</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Submodule.finrank_sup_add_finrank_inf_eq</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="n">F</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">finrank</span> <span class="n">K</span> <span class="o">(</span><span class="n">E</span> <span class="bp">⊔</span> <span class="n">F</span> <span class="o">:</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="bp">+</span> <span class="n">finrank</span> <span class="n">K</span> <span class="o">(</span><span class="n">E</span> <span class="bp">⊓</span> <span class="n">F</span> <span class="o">:</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="bp">=</span> <span class="n">finrank</span> <span class="n">K</span> <span class="n">E</span> <span class="bp">+</span> <span class="n">finrank</span> <span class="n">K</span> <span class="n">F</span> <span class="o">:=</span> <span class="n">Submodule.finrank_sup_add_finrank_inf_eq</span> <span class="n">E</span> <span class="n">F</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">finrank</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">finrank</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">Submodule.finrank_le</span><span class="w"> </span><span class="n">E</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">finrank</span> <span class="n">K</span> <span class="n">E</span> <span class="bp">≤</span> <span class="n">finrank</span> <span class="n">K</span> <span class="n">V</span> <span class="o">:=</span> <span class="n">Submodule.finrank_le</span> <span class="n">E</span> </pre></div> </div> <p>In the first statement above, the purpose of the type ascriptions is to make sure that coercion to <code class="docutils literal notranslate"><span class="pre">Type*</span></code> does not trigger too early.</p> <p>We are now ready for an exercise about <code class="docutils literal notranslate"><span class="pre">finrank</span></code> and subspaces.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">finrank</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">finrank</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">finrank</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">F</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">Nontrivial</span><span class="w"> </span><span class="o">(</span><span class="n">E</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Submodule</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">finrank</span> <span class="n">K</span> <span class="n">V</span> <span class="bp"><</span> <span class="n">finrank</span> <span class="n">K</span> <span class="n">E</span> <span class="bp">+</span> <span class="n">finrank</span> <span class="n">K</span> <span class="n">F</span><span class="o">)</span> <span class="o">:</span> <span class="n">Nontrivial</span> <span class="o">(</span><span class="n">E</span> <span class="bp">⊓</span> <span class="n">F</span> <span class="o">:</span> <span class="n">Submodule</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="kd">end</span> </pre></div> </div>
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@@ -1216,28 +1212,28 @@ a basis of <code class="docutils literal notranslate"><span class="pre">V</span>So instead it is defined as the supremum <code class="docutils literal notranslate"><span class="pre">Module.rank</span> <span class="pre">K</span> <span class="pre">V</span></code> of cardinals of all linearly independent sets in <code class="docutils literal notranslate"><span class="pre">V</span></code>. If <code class="docutils literal notranslate"><span class="pre">V</span></code> has universe level <code class="docutils literal notranslate"><span class="pre">u</span></code> then its rank has type <code class="docutils literal notranslate"><span class="pre">Cardinal.{u}</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="c1">-- Type u_2</span> <span class="k">#check</span><span class="w"> </span><span class="n">Module.rank</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="c1">-- Cardinal.{u_2}</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="n">V</span> <span class="c1">-- Type u_2</span> <span class="k">#check</span> <span class="n">Module.rank</span> <span class="n">K</span> <span class="n">V</span> <span class="c1">-- Cardinal.{u_2}</span> </pre></div> </div> <p>One can still relate this definition to bases. Indeed there is also a commutative <code class="docutils literal notranslate"><span class="pre">max</span></code> operation on universe levels, and given two universe levels <code class="docutils literal notranslate"><span class="pre">u</span></code> and <code class="docutils literal notranslate"><span class="pre">v</span></code> there is an operation <code class="docutils literal notranslate"><span class="pre">Cardinal.lift.{u,</span> <span class="pre">v}</span> <span class="pre">:</span> <span class="pre">Cardinal.{v}</span> <span class="pre">→</span> <span class="pre">Cardinal.{max</span> <span class="pre">v</span> <span class="pre">u}</span></code> that allows to put cardinals in a common universe and state the dimension theorem.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">universe</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="c1">-- `u` and `v` will denote universe levels</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">universe</span> <span class="n">u</span> <span class="n">v</span> <span class="c1">-- `u` and `v` will denote universe levels</span> <span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">ι</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="w"> </span><span class="n">u</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">B</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Basis</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span> <span class="w"> </span><span class="o">{</span><span class="n">ι'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="w"> </span><span class="n">v</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">B'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Basis</span><span class="w"> </span><span class="n">ι'</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">)</span> <span class="kd">variable</span> <span class="o">{</span><span class="n">ι</span> <span class="o">:</span> <span class="kt">Type</span> <span class="n">u</span><span class="o">}</span> <span class="o">(</span><span class="n">B</span> <span class="o">:</span> <span class="n">Basis</span> <span class="n">ι</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="o">{</span><span class="n">ι'</span> <span class="o">:</span> <span class="kt">Type</span> <span class="n">v</span><span class="o">}</span> <span class="o">(</span><span class="n">B'</span> <span class="o">:</span> <span class="n">Basis</span> <span class="n">ι'</span> <span class="n">K</span> <span class="n">V</span><span class="o">)</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Cardinal.lift</span><span class="bp">.</span><span class="o">{</span><span class="n">v</span><span class="o">,</span><span class="w"> </span><span class="n">u</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="bp">.</span><span class="n">mk</span><span class="w"> </span><span class="n">ι</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">Cardinal.lift</span><span class="bp">.</span><span class="o">{</span><span class="n">u</span><span class="o">,</span><span class="w"> </span><span class="n">v</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="bp">.</span><span class="n">mk</span><span class="w"> </span><span class="n">ι'</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">mk_eq_mk_of_basis</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="n">B'</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">Cardinal.lift.</span><span class="o">{</span><span class="n">v</span><span class="o">,</span> <span class="n">u</span><span class="o">}</span> <span class="o">(</span><span class="bp">.</span><span class="n">mk</span> <span class="n">ι</span><span class="o">)</span> <span class="bp">=</span> <span class="n">Cardinal.lift.</span><span class="o">{</span><span class="n">u</span><span class="o">,</span> <span class="n">v</span><span class="o">}</span> <span class="o">(</span><span class="bp">.</span><span class="n">mk</span> <span class="n">ι'</span><span class="o">)</span> <span class="o">:=</span> <span class="n">mk_eq_mk_of_basis</span> <span class="n">B</span> <span class="n">B'</span> </pre></div> </div> <p>We can relate the finite dimensional case to this discussion using the coercion from natural numbers to finite cardinals (or more precisely the finite cardinals which live in <code class="docutils literal notranslate"><span class="pre">Cardinal.{v}</span></code> where <code class="docutils literal notranslate"><span class="pre">v</span></code> is the universe level of <code class="docutils literal notranslate"><span class="pre">V</span></code>).</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">[</span><span class="n">FiniteDimensional</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="o">]</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="o">(</span><span class="n">Module.finrank</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Cardinal</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">Module.rank</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Module.finrank_eq_rank</span><span class="w"> </span><span class="n">K</span><span class="w"> </span><span class="n">V</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">[</span><span class="n">FiniteDimensional</span> <span class="n">K</span> <span class="n">V</span><span class="o">]</span> <span class="o">:</span> <span class="o">(</span><span class="n">Module.finrank</span> <span class="n">K</span> <span class="n">V</span> <span class="o">:</span> <span class="n">Cardinal</span><span class="o">)</span> <span class="bp">=</span> <span class="n">Module.rank</span> <span class="n">K</span> <span class="n">V</span> <span class="o">:=</span> <span class="n">Module.finrank_eq_rank</span> <span class="n">K</span> <span class="n">V</span> </pre></div> </div> </section>
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@@ -1,24 +1,24 @@<!DOCTYPE html> <html class="writer-html5" lang="en" data-content_root="./"> <html class="writer-html5" lang="en" > <head> <meta charset="utf-8" /><meta name="viewport" content="width=device-width, initial-scale=1" /> <meta charset="utf-8" /><meta name="generator" content="Docutils 0.17.1: http://docutils.sourceforge.net/" /> <meta name="viewport" content="width=device-width, initial-scale=1.0" /> <title>10. Topology — Mathematics in Lean 0.1 documentation</title> <link rel="stylesheet" type="text/css" href="_static/pygments.css?v=80d5e7a1" /> <link rel="stylesheet" type="text/css" href="_static/css/theme.css?v=e59714d7" /> <link rel="stylesheet" type="text/css" href="_static/css/custom.css?v=0731ccc3" /> <link rel="stylesheet" href="_static/pygments.css" type="text/css" /> <link rel="stylesheet" href="_static/css/theme.css" type="text/css" /> <link rel="stylesheet" href="_static/css/custom.css" type="text/css" /> <link rel="shortcut icon" href="_static/favicon.ico"/> <script src="_static/jquery.js?v=5d32c60e"></script> <script src="_static/_sphinx_javascript_frameworks_compat.js?v=2cd50e6c"></script> <script src="_static/documentation_options.js?v=2709fde1"></script> <script src="_static/doctools.js?v=9bcbadda"></script> <script src="_static/sphinx_highlight.js?v=dc90522c"></script> <script async="async" src="https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js"></script> <!--[if lt IE 9]> <script src="_static/js/html5shiv.min.js"></script> <![endif]--> <script data-url_root="./" id="documentation_options" src="_static/documentation_options.js"></script> <script src="_static/jquery.js"></script> <script src="_static/underscore.js"></script> <script src="_static/_sphinx_javascript_frameworks_compat.js"></script> <script src="_static/doctools.js"></script> <script async="async" src="https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js"></script> <script src="_static/js/theme.js"></script> <link rel="index" title="Index" href="genindex.html" /> <link rel="search" title="Search" href="search.html" />
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@@ -31,15 +31,11 @@<nav data-toggle="wy-nav-shift" class="wy-nav-side"> <div class="wy-side-scroll"> <div class="wy-side-nav-search" > <a href="index.html" class="icon icon-home"> Mathematics in Lean <a href="index.html" class="icon icon-home"> Mathematics in Lean </a> <div role="search"> <form id="rtd-search-form" class="wy-form" action="search.html" method="get"> <input type="text" name="q" placeholder="Search docs" aria-label="Search docs" /> <input type="text" name="q" placeholder="Search docs" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form>
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@@ -93,8 +89,8 @@<div class="rst-content"> <div role="navigation" aria-label="Page navigation"> <ul class="wy-breadcrumbs"> <li><a href="index.html" class="icon icon-home" aria-label="Home"></a></li> <li class="breadcrumb-item active"><span class="section-number">10. </span>Topology</li> <li><a href="index.html" class="icon icon-home"></a> »</li> <li><span class="section-number">10. </span>Topology</li> <li class="wy-breadcrumbs-aside"> <a href="_sources/C10_Topology.rst.txt" rel="nofollow"> View page source</a> </li>
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@@ -104,8 +100,8 @@<div role="main" class="document" itemscope="itemscope" itemtype="http://schema.org/Article"> <div itemprop="articleBody"> <section id="index-0"> <span id="topology"></span><span id="id1"></span><h1><span class="section-number">10. </span>Topology<a class="headerlink" href="#index-0" title="Link to this heading"></a></h1> <span class="target" id="topology"></span><section id="index-0"> <span id="id1"></span><h1><span class="section-number">10. </span>Topology<a class="headerlink" href="#index-0" title="Permalink to this heading"></a></h1> <p>Calculus is based on the concept of a function, which is used to model quantities that depend on one another. For example, it is common to study quantities that change over time.
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@@ -173,7 +169,7 @@ Formalizing mathematics requires making the relevant notion of “sameness&#fully explicit, and that is exactly what Bourbaki’s theory of filters manages to do.</p> <section id="filters"> <span id="index-1"></span><span id="id2"></span><h2><span class="section-number">10.1. </span>Filters<a class="headerlink" href="#filters" title="Link to this heading"></a></h2> <span id="index-1"></span><span id="id2"></span><h2><span class="section-number">10.1. </span>Filters<a class="headerlink" href="#filters" title="Permalink to this heading"></a></h2> <p>A <em>filter</em> on a type <code class="docutils literal notranslate"><span class="pre">X</span></code> is a collection of sets of <code class="docutils literal notranslate"><span class="pre">X</span></code> that satisfies three conditions that we will spell out below. The notion supports two related ideas:</p>
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@@ -209,28 +205,28 @@ that mention <code class="docutils literal notranslate"><span class="pre">U</spacondition then says that <code class="docutils literal notranslate"><span class="pre">univ</span></code> is sufficiently large, the second one says that a set containing a sufficiently large set is sufficiently large and the third one says that the intersection of two sufficiently large sets is sufficiently large.</p> <p>It may be even more useful to think of a filter on a type <code class="docutils literal notranslate"><span class="pre">X</span></code> <p>It may be even more useful to think of a filter on a type <code class="docutils literal notranslate"><span class="pre">X</span></code> as a generalized element of <code class="docutils literal notranslate"><span class="pre">Set</span> <span class="pre">X</span></code>. For instance, <code class="docutils literal notranslate"><span class="pre">atTop</span></code> is the “set of very large numbers” and <code class="docutils literal notranslate"><span class="pre">𝓝</span> <span class="pre">x₀</span></code> is the “set of points very close to <code class="docutils literal notranslate"><span class="pre">x₀</span></code>.” One manifestation of this view is that we can associate to any <code class="docutils literal notranslate"><span class="pre">s</span> <span class="pre">:</span> <span class="pre">Set</span> <span class="pre">X</span></code> the so-called <em>principal filter</em> consisting of all sets that contain <code class="docutils literal notranslate"><span class="pre">s</span></code>. This definition is already in Mathlib and has a notation <code class="docutils literal notranslate"><span class="pre">𝓟</span></code> (localized in the <code class="docutils literal notranslate"><span class="pre">Filter</span></code> namespace). For the purpose of demonstration, we ask you to take this opportunity to work out the definition here.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">principal</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">α</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Filter</span><span class="w"> </span><span class="n">α</span> <span class="w"> </span><span class="n">where</span> <span class="w"> </span><span class="n">sets</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="o">}</span> <span class="w"> </span><span class="n">univ_sets</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">sets_of_superset</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">inter_sets</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">principal</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">(</span><span class="n">s</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">α</span><span class="o">)</span> <span class="o">:</span> <span class="n">Filter</span> <span class="n">α</span> <span class="n">where</span> <span class="n">sets</span> <span class="o">:=</span> <span class="o">{</span> <span class="n">t</span> <span class="bp">|</span> <span class="n">s</span> <span class="bp">⊆</span> <span class="n">t</span> <span class="o">}</span> <span class="n">univ_sets</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="n">sets_of_superset</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="n">inter_sets</span> <span class="o">:=</span> <span class="gr">sorry</span> </pre></div> </div> <p>For our second example, we ask you to define the filter <code class="docutils literal notranslate"><span class="pre">atTop</span> <span class="pre">:</span> <span class="pre">Filter</span> <span class="pre">ℕ</span></code>. (We could use any type with a preorder instead of <code class="docutils literal notranslate"><span class="pre">ℕ</span></code>.)</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Filter</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">sets</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">b</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">}</span> <span class="w"> </span><span class="n">univ_sets</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">sets_of_superset</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">inter_sets</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span><span class="w"> </span><span class="o">}</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">Filter</span> <span class="n">ℕ</span> <span class="o">:=</span> <span class="o">{</span> <span class="n">sets</span> <span class="o">:=</span> <span class="o">{</span> <span class="n">s</span> <span class="bp">|</span> <span class="bp">∃</span> <span class="n">a</span><span class="o">,</span> <span class="bp">∀</span> <span class="n">b</span><span class="o">,</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">b</span> <span class="bp">→</span> <span class="n">b</span> <span class="bp">∈</span> <span class="n">s</span> <span class="o">}</span> <span class="n">univ_sets</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="n">sets_of_superset</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="n">inter_sets</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="o">}</span> </pre></div> </div> <p>We can also directly define the filter <code class="docutils literal notranslate"><span class="pre">𝓝</span> <span class="pre">x</span></code> of neighborhoods of any <code class="docutils literal notranslate"><span class="pre">x</span> <span class="pre">:</span> <span class="pre">ℝ</span></code>.
-
@@ -241,8 +237,8 @@ defined in Mathlib as <code class="docutils literal notranslate"><span class="pr<p>With these examples, we can already define what is means for a function <code class="docutils literal notranslate"><span class="pre">f</span> <span class="pre">:</span> <span class="pre">X</span> <span class="pre">→</span> <span class="pre">Y</span></code> to converge to some <code class="docutils literal notranslate"><span class="pre">G</span> <span class="pre">:</span> <span class="pre">Filter</span> <span class="pre">Y</span></code> along some <code class="docutils literal notranslate"><span class="pre">F</span> <span class="pre">:</span> <span class="pre">Filter</span> <span class="pre">X</span></code>, as follows:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">Tendsto₁</span><span class="w"> </span><span class="o">{</span><span class="n">X</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Y</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">F</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Filter</span><span class="w"> </span><span class="n">X</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Filter</span><span class="w"> </span><span class="n">Y</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">G</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">⁻¹'</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">F</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">Tendsto₁</span> <span class="o">{</span><span class="n">X</span> <span class="n">Y</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">→</span> <span class="n">Y</span><span class="o">)</span> <span class="o">(</span><span class="n">F</span> <span class="o">:</span> <span class="n">Filter</span> <span class="n">X</span><span class="o">)</span> <span class="o">(</span><span class="n">G</span> <span class="o">:</span> <span class="n">Filter</span> <span class="n">Y</span><span class="o">)</span> <span class="o">:=</span> <span class="bp">∀</span> <span class="n">V</span> <span class="bp">∈</span> <span class="n">G</span><span class="o">,</span> <span class="n">f</span> <span class="bp">⁻¹'</span> <span class="n">V</span> <span class="bp">∈</span> <span class="n">F</span> </pre></div> </div> <p>When <code class="docutils literal notranslate"><span class="pre">X</span></code> is <code class="docutils literal notranslate"><span class="pre">ℕ</span></code> and <code class="docutils literal notranslate"><span class="pre">Y</span></code> is <code class="docutils literal notranslate"><span class="pre">ℝ</span></code>, <code class="docutils literal notranslate"><span class="pre">Tendsto₁</span> <span class="pre">u</span> <span class="pre">atTop</span> <span class="pre">(𝓝</span> <span class="pre">x)</span></code> is equivalent to saying that the sequence <code class="docutils literal notranslate"><span class="pre">u</span> <span class="pre">:</span> <span class="pre">ℕ</span> <span class="pre">→</span> <span class="pre">ℝ</span></code>
-
@@ -262,12 +258,12 @@ In this examples file we’ve opened the <code class="docutils literal notra<code class="docutils literal notranslate"><span class="pre">Filter.map</span></code> can be written as <code class="docutils literal notranslate"><span class="pre">map</span></code>. This means that we can rewrite the definition of <code class="docutils literal notranslate"><span class="pre">Tendsto</span></code> using the order relation on <code class="docutils literal notranslate"><span class="pre">Filter</span> <span class="pre">Y</span></code>, which is reversed inclusion of the set of members. In other words, given <code class="docutils literal notranslate"><span class="pre">G</span> <span class="pre">H</span> <span class="pre">:</span> <span class="pre">Filter</span> <span class="pre">Y</span></code>, we have <code class="docutils literal notranslate"><span class="pre">G</span> <span class="pre">≤</span> <span class="pre">H</span> <span class="pre">↔</span> <span class="pre">∀</span> <span class="pre">V</span> <span class="pre">:</span> <span class="pre">Set</span> <span class="pre">Y,</span> <span class="pre">V</span> <span class="pre">∈</span> <span class="pre">H</span> <span class="pre">→</span> <span class="pre">V</span> <span class="pre">∈</span> <span class="pre">G</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span><span class="w"> </span><span class="n">Tendsto₂</span><span class="w"> </span><span class="o">{</span><span class="n">X</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Y</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">F</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Filter</span><span class="w"> </span><span class="n">X</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Filter</span><span class="w"> </span><span class="n">Y</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">map</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">G</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">def</span> <span class="n">Tendsto₂</span> <span class="o">{</span><span class="n">X</span> <span class="n">Y</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">→</span> <span class="n">Y</span><span class="o">)</span> <span class="o">(</span><span class="n">F</span> <span class="o">:</span> <span class="n">Filter</span> <span class="n">X</span><span class="o">)</span> <span class="o">(</span><span class="n">G</span> <span class="o">:</span> <span class="n">Filter</span> <span class="n">Y</span><span class="o">)</span> <span class="o">:=</span> <span class="n">map</span> <span class="n">f</span> <span class="n">F</span> <span class="bp">≤</span> <span class="n">G</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">X</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Y</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">F</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Filter</span><span class="w"> </span><span class="n">X</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Filter</span><span class="w"> </span><span class="n">Y</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">Tendsto₂</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">Tendsto₁</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Iff.rfl</span> <span class="kd">example</span> <span class="o">{</span><span class="n">X</span> <span class="n">Y</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">→</span> <span class="n">Y</span><span class="o">)</span> <span class="o">(</span><span class="n">F</span> <span class="o">:</span> <span class="n">Filter</span> <span class="n">X</span><span class="o">)</span> <span class="o">(</span><span class="n">G</span> <span class="o">:</span> <span class="n">Filter</span> <span class="n">Y</span><span class="o">)</span> <span class="o">:</span> <span class="n">Tendsto₂</span> <span class="n">f</span> <span class="n">F</span> <span class="n">G</span> <span class="bp">↔</span> <span class="n">Tendsto₁</span> <span class="n">f</span> <span class="n">F</span> <span class="n">G</span> <span class="o">:=</span> <span class="n">Iff.rfl</span> </pre></div> </div> <p>It may seem that the order relation on filters is backward. But recall that we can view filters on <code class="docutils literal notranslate"><span class="pre">X</span></code> as
-
@@ -283,11 +279,11 @@ The inequality means the “direct image under <code class="docutils literalIt also leverages the algebraic properties of the pushforward operation. First, each <code class="docutils literal notranslate"><span class="pre">Filter.map</span> <span class="pre">f</span></code> is monotone. And, second, <code class="docutils literal notranslate"><span class="pre">Filter.map</span></code> is compatible with composition.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="bp">@</span><span class="n">Filter.map_mono</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="n">β</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">m</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">β</span><span class="o">},</span><span class="w"> </span><span class="n">Monotone</span><span class="w"> </span><span class="o">(</span><span class="n">map</span><span class="w"> </span><span class="n">m</span><span class="o">))</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="o">(</span><span class="bp">@</span><span class="n">Filter.map_mono</span> <span class="o">:</span> <span class="bp">∀</span> <span class="o">{</span><span class="n">α</span> <span class="n">β</span><span class="o">}</span> <span class="o">{</span><span class="n">m</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">β</span><span class="o">},</span> <span class="n">Monotone</span> <span class="o">(</span><span class="n">map</span> <span class="n">m</span><span class="o">))</span> <span class="k">#check</span> <span class="w"> </span><span class="o">(</span><span class="bp">@</span><span class="n">Filter.map_map</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="n">β</span><span class="w"> </span><span class="n">γ</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Filter</span><span class="w"> </span><span class="n">α</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">m</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">β</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">m'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">β</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">γ</span><span class="o">},</span><span class="w"> </span><span class="n">map</span><span class="w"> </span><span class="n">m'</span><span class="w"> </span><span class="o">(</span><span class="n">map</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">map</span><span class="w"> </span><span class="o">(</span><span class="n">m'</span><span class="w"> </span><span class="bp">∘</span><span class="w"> </span><span class="n">m</span><span class="o">)</span><span class="w"> </span><span class="n">f</span><span class="o">)</span> <span class="o">(</span><span class="bp">@</span><span class="n">Filter.map_map</span> <span class="o">:</span> <span class="bp">∀</span> <span class="o">{</span><span class="n">α</span> <span class="n">β</span> <span class="n">γ</span><span class="o">}</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">Filter</span> <span class="n">α</span><span class="o">}</span> <span class="o">{</span><span class="n">m</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">β</span><span class="o">}</span> <span class="o">{</span><span class="n">m'</span> <span class="o">:</span> <span class="n">β</span> <span class="bp">→</span> <span class="n">γ</span><span class="o">},</span> <span class="n">map</span> <span class="n">m'</span> <span class="o">(</span><span class="n">map</span> <span class="n">m</span> <span class="n">f</span><span class="o">)</span> <span class="bp">=</span> <span class="n">map</span> <span class="o">(</span><span class="n">m'</span> <span class="bp">∘</span> <span class="n">m</span><span class="o">)</span> <span class="n">f</span><span class="o">)</span> </pre></div> </div> <p>Together these two properties allow us to prove that limits compose, yielding in one shot all 512 variants
-
@@ -296,9 +292,9 @@ You can practice proving the following statement using either the definitionof <code class="docutils literal notranslate"><span class="pre">Tendsto₁</span></code> in terms of the universal quantifier or the algebraic definition, together with the two lemmas above.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">X</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="n">Z</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">F</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Filter</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Filter</span><span class="w"> </span><span class="n">Y</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">H</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Filter</span><span class="w"> </span><span class="n">Z</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Y</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">g</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Z</span><span class="o">}</span> <span class="w"> </span><span class="o">(</span><span class="n">hf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Tendsto₁</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hg</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Tendsto₁</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="n">H</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Tendsto₁</span><span class="w"> </span><span class="o">(</span><span class="n">g</span><span class="w"> </span><span class="bp">∘</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">X</span> <span class="n">Y</span> <span class="n">Z</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">{</span><span class="n">F</span> <span class="o">:</span> <span class="n">Filter</span> <span class="n">X</span><span class="o">}</span> <span class="o">{</span><span class="n">G</span> <span class="o">:</span> <span class="n">Filter</span> <span class="n">Y</span><span class="o">}</span> <span class="o">{</span><span class="n">H</span> <span class="o">:</span> <span class="n">Filter</span> <span class="n">Z</span><span class="o">}</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">→</span> <span class="n">Y</span><span class="o">}</span> <span class="o">{</span><span class="n">g</span> <span class="o">:</span> <span class="n">Y</span> <span class="bp">→</span> <span class="n">Z</span><span class="o">}</span> <span class="o">(</span><span class="n">hf</span> <span class="o">:</span> <span class="n">Tendsto₁</span> <span class="n">f</span> <span class="n">F</span> <span class="n">G</span><span class="o">)</span> <span class="o">(</span><span class="n">hg</span> <span class="o">:</span> <span class="n">Tendsto₁</span> <span class="n">g</span> <span class="n">G</span> <span class="n">H</span><span class="o">)</span> <span class="o">:</span> <span class="n">Tendsto₁</span> <span class="o">(</span><span class="n">g</span> <span class="bp">∘</span> <span class="n">f</span><span class="o">)</span> <span class="n">F</span> <span class="n">H</span> <span class="o">:=</span> <span class="gr">sorry</span> </pre></div> </div> <p>The pushforward construction uses a map to push filters from the map source to the map target.
-
@@ -317,19 +313,19 @@ This operation could be used to provided another formulation of <code class="doc<code class="docutils literal notranslate"><span class="pre">x₀</span> <span class="pre">:</span> <span class="pre">ℝ</span></code> and <code class="docutils literal notranslate"><span class="pre">y₀</span> <span class="pre">:</span> <span class="pre">ℝ</span></code>, and suppose we want to state that <code class="docutils literal notranslate"><span class="pre">f</span> <span class="pre">x</span></code> approaches <code class="docutils literal notranslate"><span class="pre">y₀</span></code> when <code class="docutils literal notranslate"><span class="pre">x</span></code> approaches <code class="docutils literal notranslate"><span class="pre">x₀</span></code> within the rational numbers. We can pull the filter <code class="docutils literal notranslate"><span class="pre">𝓝</span> <span class="pre">x₀</span></code> back to <code class="docutils literal notranslate"><span class="pre">ℚ</span></code> using the coercion map <code class="docutils literal notranslate"><span class="pre">(↑)</span> <span class="pre">:</span> <span class="pre">ℚ</span> <span class="pre">→</span> <span class="pre">ℝ</span></code> and state <code class="docutils literal notranslate"><span class="pre">Tendsto</span> <span class="pre">(f</span> <span class="pre">∘</span> <span class="pre">(↑)</span> <span class="pre">:</span> <span class="pre">ℚ</span> <span class="pre">→</span> <span class="pre">ℝ)</span> <span class="pre">(comap</span> <span class="pre">(↑)</span> <span class="pre">(𝓝</span> <span class="pre">x₀))</span> <span class="pre">(𝓝</span> <span class="pre">y₀)</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">x₀</span><span class="w"> </span><span class="n">y₀</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">x₀</span> <span class="n">y₀</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="n">comap</span><span class="w"> </span><span class="o">((</span><span class="bp">↑</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℚ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">𝓝</span><span class="w"> </span><span class="n">x₀</span><span class="o">)</span> <span class="k">#check</span> <span class="n">comap</span> <span class="o">((</span><span class="bp">↑</span><span class="o">)</span> <span class="o">:</span> <span class="n">ℚ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="bp">𝓝</span> <span class="n">x₀</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="n">Tendsto</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="bp">∘</span><span class="w"> </span><span class="o">(</span><span class="bp">↑</span><span class="o">))</span><span class="w"> </span><span class="o">(</span><span class="n">comap</span><span class="w"> </span><span class="o">((</span><span class="bp">↑</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℚ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">𝓝</span><span class="w"> </span><span class="n">x₀</span><span class="o">))</span><span class="w"> </span><span class="o">(</span><span class="n">𝓝</span><span class="w"> </span><span class="n">y₀</span><span class="o">)</span> <span class="k">#check</span> <span class="n">Tendsto</span> <span class="o">(</span><span class="n">f</span> <span class="bp">∘</span> <span class="o">(</span><span class="bp">↑</span><span class="o">))</span> <span class="o">(</span><span class="n">comap</span> <span class="o">((</span><span class="bp">↑</span><span class="o">)</span> <span class="o">:</span> <span class="n">ℚ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="bp">𝓝</span> <span class="n">x₀</span><span class="o">))</span> <span class="o">(</span><span class="bp">𝓝</span> <span class="n">y₀</span><span class="o">)</span> </pre></div> </div> <p>The pullback operation is also compatible with composition, but it is <em>contravariant</em>, which is to say, it reverses the order of the arguments.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">section</span> <span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="n">β</span><span class="w"> </span><span class="n">γ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">F</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Filter</span><span class="w"> </span><span class="n">α</span><span class="o">)</span><span class="w"> </span><span class="o">{</span><span class="n">m</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">γ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">β</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">β</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">α</span><span class="o">}</span> <span class="kd">variable</span> <span class="o">{</span><span class="n">α</span> <span class="n">β</span> <span class="n">γ</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">(</span><span class="n">F</span> <span class="o">:</span> <span class="n">Filter</span> <span class="n">α</span><span class="o">)</span> <span class="o">{</span><span class="n">m</span> <span class="o">:</span> <span class="n">γ</span> <span class="bp">→</span> <span class="n">β</span><span class="o">}</span> <span class="o">{</span><span class="n">n</span> <span class="o">:</span> <span class="n">β</span> <span class="bp">→</span> <span class="n">α</span><span class="o">}</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">comap_comap</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">comap</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="o">(</span><span class="n">comap</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">F</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">comap</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="bp">∘</span><span class="w"> </span><span class="n">m</span><span class="o">)</span><span class="w"> </span><span class="n">F</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">comap_comap</span> <span class="o">:</span> <span class="n">comap</span> <span class="n">m</span> <span class="o">(</span><span class="n">comap</span> <span class="n">n</span> <span class="n">F</span><span class="o">)</span> <span class="bp">=</span> <span class="n">comap</span> <span class="o">(</span><span class="n">n</span> <span class="bp">∘</span> <span class="n">m</span><span class="o">)</span> <span class="n">F</span><span class="o">)</span> <span class="kd">end</span> </pre></div>
-
@@ -337,8 +333,8 @@ which is to say, it reverses the order of the arguments.</p><p>Let’s now shift attention to the plane <code class="docutils literal notranslate"><span class="pre">ℝ</span> <span class="pre">×</span> <span class="pre">ℝ</span></code> and try to understand how the neighborhoods of a point <code class="docutils literal notranslate"><span class="pre">(x₀,</span> <span class="pre">y₀)</span></code> are related to <code class="docutils literal notranslate"><span class="pre">𝓝</span> <span class="pre">x₀</span></code> and <code class="docutils literal notranslate"><span class="pre">𝓝</span> <span class="pre">y₀</span></code>. There is a product operation <code class="docutils literal notranslate"><span class="pre">Filter.prod</span> <span class="pre">:</span> <span class="pre">Filter</span> <span class="pre">X</span> <span class="pre">→</span> <span class="pre">Filter</span> <span class="pre">Y</span> <span class="pre">→</span> <span class="pre">Filter</span> <span class="pre">(X</span> <span class="pre">×</span> <span class="pre">Y)</span></code>, denoted by <code class="docutils literal notranslate"><span class="pre">×ˢ</span></code>, which answers this question:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">𝓝</span><span class="w"> </span><span class="o">(</span><span class="n">x₀</span><span class="o">,</span><span class="w"> </span><span class="n">y₀</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">𝓝</span><span class="w"> </span><span class="n">x₀</span><span class="w"> </span><span class="bp">×ˢ</span><span class="w"> </span><span class="n">𝓝</span><span class="w"> </span><span class="n">y₀</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">nhds_prod_eq</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="bp">𝓝</span> <span class="o">(</span><span class="n">x₀</span><span class="o">,</span> <span class="n">y₀</span><span class="o">)</span> <span class="bp">=</span> <span class="bp">𝓝</span> <span class="n">x₀</span> <span class="bp">×ˢ</span> <span class="bp">𝓝</span> <span class="n">y₀</span> <span class="o">:=</span> <span class="n">nhds_prod_eq</span> </pre></div> </div> <p>The product operation is defined in terms of the pullback operation and the <code class="docutils literal notranslate"><span class="pre">inf</span></code> operation:</p>
-
@@ -352,12 +348,12 @@ Thus the <code class="docutils literal notranslate"><span class="pre">inf</span>to give algebraic proofs about convergence without ever referring to members of filters. You can practice doing this in a proof of the following lemma, unfolding the definition of <code class="docutils literal notranslate"><span class="pre">Tendsto</span></code> and <code class="docutils literal notranslate"><span class="pre">Filter.prod</span></code> if needed.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="n">le_inf_iff</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="n">le_inf_iff</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">×</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">x₀</span><span class="w"> </span><span class="n">y₀</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">Tendsto</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">atTop</span><span class="w"> </span><span class="o">(</span><span class="n">𝓝</span><span class="w"> </span><span class="o">(</span><span class="n">x₀</span><span class="o">,</span><span class="w"> </span><span class="n">y₀</span><span class="o">))</span><span class="w"> </span><span class="bp">↔</span> <span class="w"> </span><span class="n">Tendsto</span><span class="w"> </span><span class="o">(</span><span class="n">Prod.fst</span><span class="w"> </span><span class="bp">∘</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="n">atTop</span><span class="w"> </span><span class="o">(</span><span class="n">𝓝</span><span class="w"> </span><span class="n">x₀</span><span class="o">)</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">Tendsto</span><span class="w"> </span><span class="o">(</span><span class="n">Prod.snd</span><span class="w"> </span><span class="bp">∘</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="n">atTop</span><span class="w"> </span><span class="o">(</span><span class="n">𝓝</span><span class="w"> </span><span class="n">y₀</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">ℝ</span> <span class="bp">×</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">x₀</span> <span class="n">y₀</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="n">Tendsto</span> <span class="n">f</span> <span class="n">atTop</span> <span class="o">(</span><span class="bp">𝓝</span> <span class="o">(</span><span class="n">x₀</span><span class="o">,</span> <span class="n">y₀</span><span class="o">))</span> <span class="bp">↔</span> <span class="n">Tendsto</span> <span class="o">(</span><span class="n">Prod.fst</span> <span class="bp">∘</span> <span class="n">f</span><span class="o">)</span> <span class="n">atTop</span> <span class="o">(</span><span class="bp">𝓝</span> <span class="n">x₀</span><span class="o">)</span> <span class="bp">∧</span> <span class="n">Tendsto</span> <span class="o">(</span><span class="n">Prod.snd</span> <span class="bp">∘</span> <span class="n">f</span><span class="o">)</span> <span class="n">atTop</span> <span class="o">(</span><span class="bp">𝓝</span> <span class="n">y₀</span><span class="o">)</span> <span class="o">:=</span> <span class="gr">sorry</span> </pre></div> </div> <p>The ordered type <code class="docutils literal notranslate"><span class="pre">Filter</span> <span class="pre">X</span></code> is actually a <em>complete</em> lattice,
-
@@ -410,8 +406,8 @@ a predicate on <code class="docutils literal notranslate"><span class="pre">_In the case of <code class="docutils literal notranslate"><span class="pre">𝓝</span> <span class="pre">x₀</span></code>, we want <code class="docutils literal notranslate"><span class="pre">ι</span></code> to be <code class="docutils literal notranslate"><span class="pre">ℝ</span></code>, we write <code class="docutils literal notranslate"><span class="pre">ε</span></code> for <code class="docutils literal notranslate"><span class="pre">i</span></code>, and the predicate should select the positive values of <code class="docutils literal notranslate"><span class="pre">ε</span></code>. So the fact that the sets <code class="docutils literal notranslate"><span class="pre">Ioo</span>  <span class="pre">(x₀</span> <span class="pre">-</span> <span class="pre">ε)</span> <span class="pre">(x₀</span> <span class="pre">+</span> <span class="pre">ε)</span></code> form a basis for the neighborhood topology on <code class="docutils literal notranslate"><span class="pre">ℝ</span></code> is stated as follows:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">x₀</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">HasBasis</span><span class="w"> </span><span class="o">(</span><span class="n">𝓝</span><span class="w"> </span><span class="n">x₀</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span><span class="o">)</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">Ioo</span><span class="w"> </span><span class="o">(</span><span class="n">x₀</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">ε</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">x₀</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">ε</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">nhds_basis_Ioo_pos</span><span class="w"> </span><span class="n">x₀</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">x₀</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="n">HasBasis</span> <span class="o">(</span><span class="bp">𝓝</span> <span class="n">x₀</span><span class="o">)</span> <span class="o">(</span><span class="k">fun</span> <span class="n">ε</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">↦</span> <span class="mi">0</span> <span class="bp"><</span> <span class="n">ε</span><span class="o">)</span> <span class="k">fun</span> <span class="n">ε</span> <span class="bp">↦</span> <span class="n">Ioo</span> <span class="o">(</span><span class="n">x₀</span> <span class="bp">-</span> <span class="n">ε</span><span class="o">)</span> <span class="o">(</span><span class="n">x₀</span> <span class="bp">+</span> <span class="n">ε</span><span class="o">)</span> <span class="o">:=</span> <span class="n">nhds_basis_Ioo_pos</span> <span class="n">x₀</span> </pre></div> </div> <p>There is also a nice basis for the filter <code class="docutils literal notranslate"><span class="pre">atTop</span></code>. The lemma
-
@@ -420,11 +416,11 @@ us to reformulate a statement of the form <code class="docutils literal notranslgiven bases for <code class="docutils literal notranslate"><span class="pre">F</span></code> and <code class="docutils literal notranslate"><span class="pre">G</span></code>. Putting these pieces together gives us essentially the notion of convergence that we used in <a class="reference internal" href="C03_Logic.html#sequences-and-convergence"><span class="std std-numref">Section 3.6</span></a>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">u</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">x₀</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">Tendsto</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="n">atTop</span><span class="w"> </span><span class="o">(</span><span class="n">𝓝</span><span class="w"> </span><span class="n">x₀</span><span class="o">)</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span><span class="o">,</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">N</span><span class="o">,</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">≥</span><span class="w"> </span><span class="n">N</span><span class="o">,</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">Ioo</span><span class="w"> </span><span class="o">(</span><span class="n">x₀</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">ε</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">x₀</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">ε</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">atTop.HasBasis</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">True</span><span class="o">)</span><span class="w"> </span><span class="n">Ici</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">atTop_basis</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">this.tendsto_iff</span><span class="w"> </span><span class="o">(</span><span class="n">nhds_basis_Ioo_pos</span><span class="w"> </span><span class="n">x₀</span><span class="o">)]</span> <span class="w"> </span><span class="n">simp</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">u</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">x₀</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="n">Tendsto</span> <span class="n">u</span> <span class="n">atTop</span> <span class="o">(</span><span class="bp">𝓝</span> <span class="n">x₀</span><span class="o">)</span> <span class="bp">↔</span> <span class="bp">∀</span> <span class="n">ε</span> <span class="bp">></span> <span class="mi">0</span><span class="o">,</span> <span class="bp">∃</span> <span class="n">N</span><span class="o">,</span> <span class="bp">∀</span> <span class="n">n</span> <span class="bp">≥</span> <span class="n">N</span><span class="o">,</span> <span class="n">u</span> <span class="n">n</span> <span class="bp">∈</span> <span class="n">Ioo</span> <span class="o">(</span><span class="n">x₀</span> <span class="bp">-</span> <span class="n">ε</span><span class="o">)</span> <span class="o">(</span><span class="n">x₀</span> <span class="bp">+</span> <span class="n">ε</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="k">have</span> <span class="o">:</span> <span class="n">atTop.HasBasis</span> <span class="o">(</span><span class="k">fun</span> <span class="n">_</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">↦</span> <span class="n">True</span><span class="o">)</span> <span class="n">Ici</span> <span class="o">:=</span> <span class="n">atTop_basis</span> <span class="n">rw</span> <span class="o">[</span><span class="n">this.tendsto_iff</span> <span class="o">(</span><span class="n">nhds_basis_Ioo_pos</span> <span class="n">x₀</span><span class="o">)]</span> <span class="n">simp</span> </pre></div> </div> <p>We now show how filters facilitate working with properties that hold for sufficiently large numbers
-
@@ -444,9 +440,9 @@ but we can use the more suggestive notation <code class="docutils literal notranHere the superscripted <code class="docutils literal notranslate"><span class="pre">f</span></code> stands for “Filter.” You can think of the notation as saying that for all <code class="docutils literal notranslate"><span class="pre">n</span></code> in the “set of very large numbers,” <code class="docutils literal notranslate"><span class="pre">P</span> <span class="pre">n</span></code> holds. The <code class="docutils literal notranslate"><span class="pre">∀ᶠ</span></code> notation stands for <code class="docutils literal notranslate"><span class="pre">Filter.Eventually</span></code>, and the lemma <code class="docutils literal notranslate"><span class="pre">Filter.Eventually.and</span></code> uses the intersection property of filters to do what we just described:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">P</span><span class="w"> </span><span class="n">Q</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="kt">Prop</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hP</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀ᶠ</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">atTop</span><span class="o">,</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hQ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀ᶠ</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">atTop</span><span class="o">,</span><span class="w"> </span><span class="n">Q</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="bp">∀ᶠ</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">atTop</span><span class="o">,</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">Q</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">hP.and</span><span class="w"> </span><span class="n">hQ</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">P</span> <span class="n">Q</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="kt">Prop</span><span class="o">)</span> <span class="o">(</span><span class="n">hP</span> <span class="o">:</span> <span class="bp">∀ᶠ</span> <span class="n">n</span> <span class="k">in</span> <span class="n">atTop</span><span class="o">,</span> <span class="n">P</span> <span class="n">n</span><span class="o">)</span> <span class="o">(</span><span class="n">hQ</span> <span class="o">:</span> <span class="bp">∀ᶠ</span> <span class="n">n</span> <span class="k">in</span> <span class="n">atTop</span><span class="o">,</span> <span class="n">Q</span> <span class="n">n</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∀ᶠ</span> <span class="n">n</span> <span class="k">in</span> <span class="n">atTop</span><span class="o">,</span> <span class="n">P</span> <span class="n">n</span> <span class="bp">∧</span> <span class="n">Q</span> <span class="n">n</span> <span class="o">:=</span> <span class="n">hP.and</span> <span class="n">hQ</span> </pre></div> </div> <p>This notation is so convenient and intuitive that we also have specializations
-
@@ -457,13 +453,13 @@ two sequences of real numbers, and let us show that ifFirst we’ll use the generic <code class="docutils literal notranslate"><span class="pre">Eventually</span></code> and then the one specialized for the equality predicate, <code class="docutils literal notranslate"><span class="pre">EventuallyEq</span></code>. The two statements are definitionally equivalent so the same proof work in both cases.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">u</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀ᶠ</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">atTop</span><span class="o">,</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">x₀</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">Tendsto</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="n">atTop</span><span class="w"> </span><span class="o">(</span><span class="n">𝓝</span><span class="w"> </span><span class="n">x₀</span><span class="o">)</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">Tendsto</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="n">atTop</span><span class="w"> </span><span class="o">(</span><span class="n">𝓝</span><span class="w"> </span><span class="n">x₀</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">tendsto_congr'</span><span class="w"> </span><span class="n">h</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">u</span> <span class="n">v</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="bp">∀ᶠ</span> <span class="n">n</span> <span class="k">in</span> <span class="n">atTop</span><span class="o">,</span> <span class="n">u</span> <span class="n">n</span> <span class="bp">=</span> <span class="n">v</span> <span class="n">n</span><span class="o">)</span> <span class="o">(</span><span class="n">x₀</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="n">Tendsto</span> <span class="n">u</span> <span class="n">atTop</span> <span class="o">(</span><span class="bp">𝓝</span> <span class="n">x₀</span><span class="o">)</span> <span class="bp">↔</span> <span class="n">Tendsto</span> <span class="n">v</span> <span class="n">atTop</span> <span class="o">(</span><span class="bp">𝓝</span> <span class="n">x₀</span><span class="o">)</span> <span class="o">:=</span> <span class="n">tendsto_congr'</span> <span class="n">h</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">u</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="bp">=ᶠ</span><span class="o">[</span><span class="n">atTop</span><span class="o">]</span><span class="w"> </span><span class="n">v</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">x₀</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">Tendsto</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="n">atTop</span><span class="w"> </span><span class="o">(</span><span class="n">𝓝</span><span class="w"> </span><span class="n">x₀</span><span class="o">)</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">Tendsto</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="n">atTop</span><span class="w"> </span><span class="o">(</span><span class="n">𝓝</span><span class="w"> </span><span class="n">x₀</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">tendsto_congr'</span><span class="w"> </span><span class="n">h</span> <span class="kd">example</span> <span class="o">(</span><span class="n">u</span> <span class="n">v</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">u</span> <span class="bp">=ᶠ</span><span class="o">[</span><span class="n">atTop</span><span class="o">]</span> <span class="n">v</span><span class="o">)</span> <span class="o">(</span><span class="n">x₀</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="n">Tendsto</span> <span class="n">u</span> <span class="n">atTop</span> <span class="o">(</span><span class="bp">𝓝</span> <span class="n">x₀</span><span class="o">)</span> <span class="bp">↔</span> <span class="n">Tendsto</span> <span class="n">v</span> <span class="n">atTop</span> <span class="o">(</span><span class="bp">𝓝</span> <span class="n">x₀</span><span class="o">)</span> <span class="o">:=</span> <span class="n">tendsto_congr'</span> <span class="n">h</span> </pre></div> </div> <p>It is instructive to review the definition of filters in terms of <code class="docutils literal notranslate"><span class="pre">Eventually</span></code>.
-
@@ -473,25 +469,25 @@ Given <code class="docutils literal notranslate"><span class="pre">F</span> <spa<li><p>the condition <code class="docutils literal notranslate"><span class="pre">U</span> <span class="pre">∈</span> <span class="pre">F</span> <span class="pre">→</span> <span class="pre">U</span> <span class="pre">⊆</span> <span class="pre">V</span> <span class="pre">→</span> <span class="pre">V</span> <span class="pre">∈</span> <span class="pre">F</span></code> ensures <code class="docutils literal notranslate"><span class="pre">(∀ᶠ</span> <span class="pre">x</span> <span class="pre">in</span> <span class="pre">F,</span> <span class="pre">P</span> <span class="pre">x)</span> <span class="pre">→</span> <span class="pre">(∀</span> <span class="pre">x,</span> <span class="pre">P</span> <span class="pre">x</span> <span class="pre">→</span> <span class="pre">Q</span> <span class="pre">x)</span> <span class="pre">→</span> <span class="pre">∀ᶠ</span> <span class="pre">x</span> <span class="pre">in</span> <span class="pre">F,</span> <span class="pre">Q</span> <span class="pre">x</span></code>, and</p></li> <li><p>the condition <code class="docutils literal notranslate"><span class="pre">U</span> <span class="pre">∈</span> <span class="pre">F</span> <span class="pre">→</span> <span class="pre">V</span> <span class="pre">∈</span> <span class="pre">F</span> <span class="pre">→</span> <span class="pre">U</span> <span class="pre">∩</span> <span class="pre">V</span> <span class="pre">∈</span> <span class="pre">F</span></code> ensures <code class="docutils literal notranslate"><span class="pre">(∀ᶠ</span> <span class="pre">x</span> <span class="pre">in</span> <span class="pre">F,</span> <span class="pre">P</span> <span class="pre">x)</span> <span class="pre">→</span> <span class="pre">(∀ᶠ</span> <span class="pre">x</span> <span class="pre">in</span> <span class="pre">F,</span> <span class="pre">Q</span> <span class="pre">x)</span> <span class="pre">→</span> <span class="pre">∀ᶠ</span> <span class="pre">x</span> <span class="pre">in</span> <span class="pre">F,</span> <span class="pre">P</span> <span class="pre">x</span> <span class="pre">∧</span> <span class="pre">Q</span> <span class="pre">x</span></code>.</p></li> </ul> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="n">Eventually.of_forall</span> <span class="k">#check</span><span class="w"> </span><span class="n">Eventually.mono</span> <span class="k">#check</span><span class="w"> </span><span class="n">Eventually.and</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="n">Eventually.of_forall</span> <span class="k">#check</span> <span class="n">Eventually.mono</span> <span class="k">#check</span> <span class="n">Eventually.and</span> </pre></div> </div> <p>The second item, corresponding to <code class="docutils literal notranslate"><span class="pre">Eventually.mono</span></code>, supports nice ways of using filters, especially when combined with <code class="docutils literal notranslate"><span class="pre">Eventually.and</span></code>. The <code class="docutils literal notranslate"><span class="pre">filter_upwards</span></code> tactic allows us to combine them. Compare:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">P</span><span class="w"> </span><span class="n">Q</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="kt">Prop</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hP</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀ᶠ</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">atTop</span><span class="o">,</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hQ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀ᶠ</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">atTop</span><span class="o">,</span><span class="w"> </span><span class="n">Q</span><span class="w"> </span><span class="n">n</span><span class="o">)</span> <span class="w"> </span><span class="o">(</span><span class="n">hR</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀ᶠ</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">atTop</span><span class="o">,</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">Q</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀ᶠ</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">atTop</span><span class="o">,</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="o">(</span><span class="n">hP.and</span><span class="w"> </span><span class="o">(</span><span class="n">hQ.and</span><span class="w"> </span><span class="n">hR</span><span class="o">))</span><span class="bp">.</span><span class="n">mono</span> <span class="w"> </span><span class="n">rintro</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">⟨</span><span class="n">h</span><span class="o">,</span><span class="w"> </span><span class="n">h'</span><span class="o">,</span><span class="w"> </span><span class="n">h''</span><span class="o">⟩</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">h''</span><span class="w"> </span><span class="o">⟨</span><span class="n">h</span><span class="o">,</span><span class="w"> </span><span class="n">h'</span><span class="o">⟩</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">P</span> <span class="n">Q</span> <span class="n">R</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="kt">Prop</span><span class="o">)</span> <span class="o">(</span><span class="n">hP</span> <span class="o">:</span> <span class="bp">∀ᶠ</span> <span class="n">n</span> <span class="k">in</span> <span class="n">atTop</span><span class="o">,</span> <span class="n">P</span> <span class="n">n</span><span class="o">)</span> <span class="o">(</span><span class="n">hQ</span> <span class="o">:</span> <span class="bp">∀ᶠ</span> <span class="n">n</span> <span class="k">in</span> <span class="n">atTop</span><span class="o">,</span> <span class="n">Q</span> <span class="n">n</span><span class="o">)</span> <span class="o">(</span><span class="n">hR</span> <span class="o">:</span> <span class="bp">∀ᶠ</span> <span class="n">n</span> <span class="k">in</span> <span class="n">atTop</span><span class="o">,</span> <span class="n">P</span> <span class="n">n</span> <span class="bp">∧</span> <span class="n">Q</span> <span class="n">n</span> <span class="bp">→</span> <span class="n">R</span> <span class="n">n</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∀ᶠ</span> <span class="n">n</span> <span class="k">in</span> <span class="n">atTop</span><span class="o">,</span> <span class="n">R</span> <span class="n">n</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">apply</span> <span class="o">(</span><span class="n">hP.and</span> <span class="o">(</span><span class="n">hQ.and</span> <span class="n">hR</span><span class="o">))</span><span class="bp">.</span><span class="n">mono</span> <span class="n">rintro</span> <span class="n">n</span> <span class="o">⟨</span><span class="n">h</span><span class="o">,</span> <span class="n">h'</span><span class="o">,</span> <span class="n">h''</span><span class="o">⟩</span> <span class="n">exact</span> <span class="n">h''</span> <span class="o">⟨</span><span class="n">h</span><span class="o">,</span> <span class="n">h'</span><span class="o">⟩</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">P</span><span class="w"> </span><span class="n">Q</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="kt">Prop</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hP</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀ᶠ</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">atTop</span><span class="o">,</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hQ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀ᶠ</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">atTop</span><span class="o">,</span><span class="w"> </span><span class="n">Q</span><span class="w"> </span><span class="n">n</span><span class="o">)</span> <span class="w"> </span><span class="o">(</span><span class="n">hR</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀ᶠ</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">atTop</span><span class="o">,</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">Q</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀ᶠ</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">atTop</span><span class="o">,</span><span class="w"> </span><span class="n">R</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">filter_upwards</span><span class="w"> </span><span class="o">[</span><span class="n">hP</span><span class="o">,</span><span class="w"> </span><span class="n">hQ</span><span class="o">,</span><span class="w"> </span><span class="n">hR</span><span class="o">]</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="n">h'</span><span class="w"> </span><span class="n">h''</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">h''</span><span class="w"> </span><span class="o">⟨</span><span class="n">h</span><span class="o">,</span><span class="w"> </span><span class="n">h'</span><span class="o">⟩</span> <span class="kd">example</span> <span class="o">(</span><span class="n">P</span> <span class="n">Q</span> <span class="n">R</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="kt">Prop</span><span class="o">)</span> <span class="o">(</span><span class="n">hP</span> <span class="o">:</span> <span class="bp">∀ᶠ</span> <span class="n">n</span> <span class="k">in</span> <span class="n">atTop</span><span class="o">,</span> <span class="n">P</span> <span class="n">n</span><span class="o">)</span> <span class="o">(</span><span class="n">hQ</span> <span class="o">:</span> <span class="bp">∀ᶠ</span> <span class="n">n</span> <span class="k">in</span> <span class="n">atTop</span><span class="o">,</span> <span class="n">Q</span> <span class="n">n</span><span class="o">)</span> <span class="o">(</span><span class="n">hR</span> <span class="o">:</span> <span class="bp">∀ᶠ</span> <span class="n">n</span> <span class="k">in</span> <span class="n">atTop</span><span class="o">,</span> <span class="n">P</span> <span class="n">n</span> <span class="bp">∧</span> <span class="n">Q</span> <span class="n">n</span> <span class="bp">→</span> <span class="n">R</span> <span class="n">n</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∀ᶠ</span> <span class="n">n</span> <span class="k">in</span> <span class="n">atTop</span><span class="o">,</span> <span class="n">R</span> <span class="n">n</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">filter_upwards</span> <span class="o">[</span><span class="n">hP</span><span class="o">,</span> <span class="n">hQ</span><span class="o">,</span> <span class="n">hR</span><span class="o">]</span> <span class="k">with</span> <span class="n">n</span> <span class="n">h</span> <span class="n">h'</span> <span class="n">h''</span> <span class="n">exact</span> <span class="n">h''</span> <span class="o">⟨</span><span class="n">h</span><span class="o">,</span> <span class="n">h'</span><span class="o">⟩</span> </pre></div> </div> <p>Readers who know about measure theory will note that the filter <code class="docutils literal notranslate"><span class="pre">μ.ae</span></code> of sets whose complement has measure zero
-
@@ -516,29 +512,29 @@ topology library.See if you can prove it using the quoted lemmas, using the fact that <code class="docutils literal notranslate"><span class="pre">ClusterPt</span> <span class="pre">x</span> <span class="pre">F</span></code> means <code class="docutils literal notranslate"><span class="pre">(𝓝</span> <span class="pre">x</span> <span class="pre">⊓</span> <span class="pre">F).NeBot</span></code> and that, by definition, the assumption <code class="docutils literal notranslate"><span class="pre">∀ᶠ</span> <span class="pre">n</span> <span class="pre">in</span> <span class="pre">atTop,</span> <span class="pre">u</span> <span class="pre">n</span> <span class="pre">∈</span> <span class="pre">M</span></code> means <code class="docutils literal notranslate"><span class="pre">M</span> <span class="pre">∈</span> <span class="pre">map</span> <span class="pre">u</span> <span class="pre">atTop</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span><span class="w"> </span><span class="n">mem_closure_iff_clusterPt</span> <span class="k">#check</span><span class="w"> </span><span class="n">le_principal_iff</span> <span class="k">#check</span><span class="w"> </span><span class="n">neBot_of_le</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="k">#check</span> <span class="n">mem_closure_iff_clusterPt</span> <span class="k">#check</span> <span class="n">le_principal_iff</span> <span class="k">#check</span> <span class="n">neBot_of_le</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">u</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">M</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hux</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Tendsto</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="n">atTop</span><span class="w"> </span><span class="o">(</span><span class="n">𝓝</span><span class="w"> </span><span class="n">x</span><span class="o">))</span> <span class="w"> </span><span class="o">(</span><span class="n">huM</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀ᶠ</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">atTop</span><span class="o">,</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">M</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">closure</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <span class="kd">example</span> <span class="o">(</span><span class="n">u</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">M</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">hux</span> <span class="o">:</span> <span class="n">Tendsto</span> <span class="n">u</span> <span class="n">atTop</span> <span class="o">(</span><span class="bp">𝓝</span> <span class="n">x</span><span class="o">))</span> <span class="o">(</span><span class="n">huM</span> <span class="o">:</span> <span class="bp">∀ᶠ</span> <span class="n">n</span> <span class="k">in</span> <span class="n">atTop</span><span class="o">,</span> <span class="n">u</span> <span class="n">n</span> <span class="bp">∈</span> <span class="n">M</span><span class="o">)</span> <span class="o">:</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">closure</span> <span class="n">M</span> <span class="o">:=</span> <span class="gr">sorry</span> </pre></div> </div> </section> <section id="metric-spaces"> <span id="index-2"></span><span id="id3"></span><h2><span class="section-number">10.2. </span>Metric spaces<a class="headerlink" href="#metric-spaces" title="Link to this heading"></a></h2> <span id="index-2"></span><span id="id3"></span><h2><span class="section-number">10.2. </span>Metric spaces<a class="headerlink" href="#metric-spaces" title="Permalink to this heading"></a></h2> <p>Examples in the previous section focus on sequences of real numbers. In this section we will go up a bit in generality and focus on metric spaces. A metric space is a type <code class="docutils literal notranslate"><span class="pre">X</span></code> equipped with a distance function <code class="docutils literal notranslate"><span class="pre">dist</span> <span class="pre">:</span> <span class="pre">X</span> <span class="pre">→</span> <span class="pre">X</span> <span class="pre">→</span> <span class="pre">ℝ</span></code> which is a generalization of the function <code class="docutils literal notranslate"><span class="pre">fun</span> <span class="pre">x</span> <span class="pre">y</span> <span class="pre">↦</span> <span class="pre">|x</span> <span class="pre">-</span> <span class="pre">y|</span></code> from the case where <code class="docutils literal notranslate"><span class="pre">X</span> <span class="pre">=</span> <span class="pre">ℝ</span></code>.</p> <p>Introducing such a space is easy and we will check all properties required from the distance function.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">X</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">MetricSpace</span><span class="w"> </span><span class="n">X</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">X</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">MetricSpace</span> <span class="n">X</span><span class="o">]</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">X</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">dist</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">dist_nonneg</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">dist_eq_zero</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">b</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">dist_comm</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">a</span><span class="o">)</span> <span class="k">#check</span><span class="w"> </span><span class="o">(</span><span class="n">dist_triangle</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">c</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">dist</span> <span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">dist_nonneg</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp">≤</span> <span class="n">dist</span> <span class="n">a</span> <span class="n">b</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">dist_eq_zero</span> <span class="o">:</span> <span class="n">dist</span> <span class="n">a</span> <span class="n">b</span> <span class="bp">=</span> <span class="mi">0</span> <span class="bp">↔</span> <span class="n">a</span> <span class="bp">=</span> <span class="n">b</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">dist_comm</span> <span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">dist</span> <span class="n">a</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">dist</span> <span class="n">b</span> <span class="n">a</span><span class="o">)</span> <span class="k">#check</span> <span class="o">(</span><span class="n">dist_triangle</span> <span class="n">a</span> <span class="n">b</span> <span class="n">c</span> <span class="o">:</span> <span class="n">dist</span> <span class="n">a</span> <span class="n">c</span> <span class="bp">≤</span> <span class="n">dist</span> <span class="n">a</span> <span class="n">b</span> <span class="bp">+</span> <span class="n">dist</span> <span class="n">b</span> <span class="n">c</span><span class="o">)</span> </pre></div> </div> <p>Note we also have variants where the distance can be infinite or where <code class="docutils literal notranslate"><span class="pre">dist</span> <span class="pre">a</span> <span class="pre">b</span></code> can be zero without having <code class="docutils literal notranslate"><span class="pre">a</span> <span class="pre">=</span> <span class="pre">b</span></code> or both.
-
@@ -546,18 +542,18 @@ They are called <code class="docutils literal notranslate"><span class="pre">EMe<p>Note that our journey from <code class="docutils literal notranslate"><span class="pre">ℝ</span></code> to metric spaces jumped over the special case of normed spaces that also require linear algebra and will be explained as part of the calculus chapter.</p> <section id="convergence-and-continuity"> <h3><span class="section-number">10.2.1. </span>Convergence and continuity<a class="headerlink" href="#convergence-and-continuity" title="Link to this heading"></a></h3> <h3><span class="section-number">10.2.1. </span>Convergence and continuity<a class="headerlink" href="#convergence-and-continuity" title="Permalink to this heading"></a></h3> <p>Using distance functions, we can already define convergent sequences and continuous functions between metric spaces. They are actually defined in a more general setting covered in the next section, but we have lemmas recasting the definition in terms of distances.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">u</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">Tendsto</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="n">atTop</span><span class="w"> </span><span class="o">(</span><span class="n">𝓝</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span><span class="o">,</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">N</span><span class="o">,</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">≥</span><span class="w"> </span><span class="n">N</span><span class="o">,</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="o">(</span><span class="n">u</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Metric.tendsto_atTop</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">u</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">X</span><span class="o">}</span> <span class="o">{</span><span class="n">a</span> <span class="o">:</span> <span class="n">X</span><span class="o">}</span> <span class="o">:</span> <span class="n">Tendsto</span> <span class="n">u</span> <span class="n">atTop</span> <span class="o">(</span><span class="bp">𝓝</span> <span class="n">a</span><span class="o">)</span> <span class="bp">↔</span> <span class="bp">∀</span> <span class="n">ε</span> <span class="bp">></span> <span class="mi">0</span><span class="o">,</span> <span class="bp">∃</span> <span class="n">N</span><span class="o">,</span> <span class="bp">∀</span> <span class="n">n</span> <span class="bp">≥</span> <span class="n">N</span><span class="o">,</span> <span class="n">dist</span> <span class="o">(</span><span class="n">u</span> <span class="n">n</span><span class="o">)</span> <span class="n">a</span> <span class="bp"><</span> <span class="n">ε</span> <span class="o">:=</span> <span class="n">Metric.tendsto_atTop</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">X</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">MetricSpace</span><span class="w"> </span><span class="n">X</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">MetricSpace</span><span class="w"> </span><span class="n">Y</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Y</span><span class="o">}</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">Continuous</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">↔</span> <span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="o">,</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span><span class="o">,</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">δ</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span><span class="o">,</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x'</span><span class="o">,</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="n">x'</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">δ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">x'</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Metric.continuous_iff</span> <span class="kd">example</span> <span class="o">{</span><span class="n">X</span> <span class="n">Y</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">MetricSpace</span> <span class="n">X</span><span class="o">]</span> <span class="o">[</span><span class="n">MetricSpace</span> <span class="n">Y</span><span class="o">]</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">→</span> <span class="n">Y</span><span class="o">}</span> <span class="o">:</span> <span class="n">Continuous</span> <span class="n">f</span> <span class="bp">↔</span> <span class="bp">∀</span> <span class="n">x</span> <span class="o">:</span> <span class="n">X</span><span class="o">,</span> <span class="bp">∀</span> <span class="n">ε</span> <span class="bp">></span> <span class="mi">0</span><span class="o">,</span> <span class="bp">∃</span> <span class="n">δ</span> <span class="bp">></span> <span class="mi">0</span><span class="o">,</span> <span class="bp">∀</span> <span class="n">x'</span><span class="o">,</span> <span class="n">dist</span> <span class="n">x'</span> <span class="n">x</span> <span class="bp"><</span> <span class="n">δ</span> <span class="bp">→</span> <span class="n">dist</span> <span class="o">(</span><span class="n">f</span> <span class="n">x'</span><span class="o">)</span> <span class="o">(</span><span class="n">f</span> <span class="n">x</span><span class="o">)</span> <span class="bp"><</span> <span class="n">ε</span> <span class="o">:=</span> <span class="n">Metric.continuous_iff</span> </pre></div> </div> <p id="index-3">A <em>lot</em> of lemmas have some continuity assumptions, so we end up proving a lot of continuity results and there
-
@@ -565,8 +561,8 @@ is a <code class="docutils literal notranslate"><span class="pre">continuity</spin an exercise below. Notice that Lean knows how to treat a product of two metric spaces as a metric space, so it makes sense to consider continuous functions from <code class="docutils literal notranslate"><span class="pre">X</span> <span class="pre">×</span> <span class="pre">X</span></code> to <code class="docutils literal notranslate"><span class="pre">ℝ</span></code>. In particular the (uncurried version of the) distance function is such a function.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">X</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">MetricSpace</span><span class="w"> </span><span class="n">X</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">MetricSpace</span><span class="w"> </span><span class="n">Y</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Y</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Continuous</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">Continuous</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">×</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">p</span><span class="bp">.</span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">p</span><span class="bp">.</span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">continuity</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">X</span> <span class="n">Y</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">MetricSpace</span> <span class="n">X</span><span class="o">]</span> <span class="o">[</span><span class="n">MetricSpace</span> <span class="n">Y</span><span class="o">]</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">→</span> <span class="n">Y</span><span class="o">}</span> <span class="o">(</span><span class="n">hf</span> <span class="o">:</span> <span class="n">Continuous</span> <span class="n">f</span><span class="o">)</span> <span class="o">:</span> <span class="n">Continuous</span> <span class="k">fun</span> <span class="n">p</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">×</span> <span class="n">X</span> <span class="bp">↦</span> <span class="n">dist</span> <span class="o">(</span><span class="n">f</span> <span class="n">p.1</span><span class="o">)</span> <span class="o">(</span><span class="n">f</span> <span class="n">p.2</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">continuity</span> </pre></div> </div> <p>This tactic is a bit slow, so it is also useful to know
-
@@ -580,9 +576,9 @@ We can do the same for the second component to get continuity of <code class="dothose two continuities using <code class="docutils literal notranslate"><span class="pre">Continuous.prod_mk</span></code> to get <code class="docutils literal notranslate"><span class="pre">(hf.comp</span> <span class="pre">continuous_fst).prod_mk</span> <span class="pre">(hf.comp</span> <span class="pre">continuous_snd)</span> <span class="pre">:</span> <span class="pre">Continuous</span> <span class="pre">(fun</span> <span class="pre">p</span> <span class="pre">:</span> <span class="pre">X</span> <span class="pre">×</span> <span class="pre">X</span> <span class="pre">↦</span> <span class="pre">(f</span> <span class="pre">p.1,</span> <span class="pre">f</span> <span class="pre">p.2))</span></code> and compose once more to get our full proof.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">X</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">MetricSpace</span><span class="w"> </span><span class="n">X</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">MetricSpace</span><span class="w"> </span><span class="n">Y</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Y</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Continuous</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">Continuous</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">×</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">p</span><span class="bp">.</span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">p</span><span class="bp">.</span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">continuous_dist.comp</span><span class="w"> </span><span class="o">((</span><span class="n">hf.comp</span><span class="w"> </span><span class="n">continuous_fst</span><span class="o">)</span><span class="bp">.</span><span class="n">prod_mk</span><span class="w"> </span><span class="o">(</span><span class="n">hf.comp</span><span class="w"> </span><span class="n">continuous_snd</span><span class="o">))</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">X</span> <span class="n">Y</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">MetricSpace</span> <span class="n">X</span><span class="o">]</span> <span class="o">[</span><span class="n">MetricSpace</span> <span class="n">Y</span><span class="o">]</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">→</span> <span class="n">Y</span><span class="o">}</span> <span class="o">(</span><span class="n">hf</span> <span class="o">:</span> <span class="n">Continuous</span> <span class="n">f</span><span class="o">)</span> <span class="o">:</span> <span class="n">Continuous</span> <span class="k">fun</span> <span class="n">p</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">×</span> <span class="n">X</span> <span class="bp">↦</span> <span class="n">dist</span> <span class="o">(</span><span class="n">f</span> <span class="n">p.1</span><span class="o">)</span> <span class="o">(</span><span class="n">f</span> <span class="n">p.2</span><span class="o">)</span> <span class="o">:=</span> <span class="n">continuous_dist.comp</span> <span class="o">((</span><span class="n">hf.comp</span> <span class="n">continuous_fst</span><span class="o">)</span><span class="bp">.</span><span class="n">prod_mk</span> <span class="o">(</span><span class="n">hf.comp</span> <span class="n">continuous_snd</span><span class="o">))</span> </pre></div> </div> <p>The combination of <code class="docutils literal notranslate"><span class="pre">Continuous.prod_mk</span></code> and <code class="docutils literal notranslate"><span class="pre">continuous_dist</span></code> via <code class="docutils literal notranslate"><span class="pre">Continuous.comp</span></code> feels clunky,
-
@@ -598,15 +594,15 @@ composition and refuse to apply this lemma. It is especially bad at this when pr<code class="docutils literal notranslate"><span class="pre">Continuous.dist</span> <span class="pre">{f</span> <span class="pre">g</span> <span class="pre">:</span> <span class="pre">X</span> <span class="pre">→</span> <span class="pre">Y}</span> <span class="pre">:</span> <span class="pre">Continuous</span> <span class="pre">f</span> <span class="pre">→</span> <span class="pre">Continuous</span> <span class="pre">g</span> <span class="pre">→</span> <span class="pre">Continuous</span> <span class="pre">(fun</span> <span class="pre">x</span> <span class="pre">↦</span> <span class="pre">dist</span> <span class="pre">(f</span> <span class="pre">x)</span> <span class="pre">(g</span> <span class="pre">x))</span></code> which is nicer to Lean’s elaborator and also provides a shorter proof when directly providing a full proof term, as can be seen from the following two new proofs of the above statement:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">X</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">MetricSpace</span><span class="w"> </span><span class="n">X</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">MetricSpace</span><span class="w"> </span><span class="n">Y</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Y</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Continuous</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">Continuous</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">×</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">p</span><span class="bp">.</span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">p</span><span class="bp">.</span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">apply</span><span class="w"> </span><span class="n">Continuous.dist</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">hf.comp</span><span class="w"> </span><span class="n">continuous_fst</span> <span class="w"> </span><span class="n">exact</span><span class="w"> </span><span class="n">hf.comp</span><span class="w"> </span><span class="n">continuous_snd</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">X</span> <span class="n">Y</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">MetricSpace</span> <span class="n">X</span><span class="o">]</span> <span class="o">[</span><span class="n">MetricSpace</span> <span class="n">Y</span><span class="o">]</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">→</span> <span class="n">Y</span><span class="o">}</span> <span class="o">(</span><span class="n">hf</span> <span class="o">:</span> <span class="n">Continuous</span> <span class="n">f</span><span class="o">)</span> <span class="o">:</span> <span class="n">Continuous</span> <span class="k">fun</span> <span class="n">p</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">×</span> <span class="n">X</span> <span class="bp">↦</span> <span class="n">dist</span> <span class="o">(</span><span class="n">f</span> <span class="n">p.1</span><span class="o">)</span> <span class="o">(</span><span class="n">f</span> <span class="n">p.2</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">apply</span> <span class="n">Continuous.dist</span> <span class="n">exact</span> <span class="n">hf.comp</span> <span class="n">continuous_fst</span> <span class="n">exact</span> <span class="n">hf.comp</span> <span class="n">continuous_snd</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">X</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">MetricSpace</span><span class="w"> </span><span class="n">X</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">MetricSpace</span><span class="w"> </span><span class="n">Y</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Y</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Continuous</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">Continuous</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">×</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">p</span><span class="bp">.</span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">p</span><span class="bp">.</span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">(</span><span class="n">hf.comp</span><span class="w"> </span><span class="n">continuous_fst</span><span class="o">)</span><span class="bp">.</span><span class="n">dist</span><span class="w"> </span><span class="o">(</span><span class="n">hf.comp</span><span class="w"> </span><span class="n">continuous_snd</span><span class="o">)</span> <span class="kd">example</span> <span class="o">{</span><span class="n">X</span> <span class="n">Y</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">MetricSpace</span> <span class="n">X</span><span class="o">]</span> <span class="o">[</span><span class="n">MetricSpace</span> <span class="n">Y</span><span class="o">]</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">→</span> <span class="n">Y</span><span class="o">}</span> <span class="o">(</span><span class="n">hf</span> <span class="o">:</span> <span class="n">Continuous</span> <span class="n">f</span><span class="o">)</span> <span class="o">:</span> <span class="n">Continuous</span> <span class="k">fun</span> <span class="n">p</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">×</span> <span class="n">X</span> <span class="bp">↦</span> <span class="n">dist</span> <span class="o">(</span><span class="n">f</span> <span class="n">p.1</span><span class="o">)</span> <span class="o">(</span><span class="n">f</span> <span class="n">p.2</span><span class="o">)</span> <span class="o">:=</span> <span class="o">(</span><span class="n">hf.comp</span> <span class="n">continuous_fst</span><span class="o">)</span><span class="bp">.</span><span class="n">dist</span> <span class="o">(</span><span class="n">hf.comp</span> <span class="n">continuous_snd</span><span class="o">)</span> </pre></div> </div> <p>Note that, without the elaboration issue coming from composition, another way to compress
-
@@ -616,66 +612,66 @@ as an alternate proof term <code class="docutils literal notranslate"><span clasto type, let us wrap this discussion with a last bit of compression offered by <code class="docutils literal notranslate"><span class="pre">Continuous.fst'</span></code> which allows to compress <code class="docutils literal notranslate"><span class="pre">hf.comp</span> <span class="pre">continuous_fst</span></code> to <code class="docutils literal notranslate"><span class="pre">hf.fst'</span></code> (and the same with <code class="docutils literal notranslate"><span class="pre">snd</span></code>) and get our final proof, now bordering obfuscation.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">X</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">MetricSpace</span><span class="w"> </span><span class="n">X</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">MetricSpace</span><span class="w"> </span><span class="n">Y</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Y</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Continuous</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">Continuous</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">×</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">p</span><span class="bp">.</span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">p</span><span class="bp">.</span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">hf.fst'.dist</span><span class="w"> </span><span class="n">hf.snd'</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">X</span> <span class="n">Y</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">MetricSpace</span> <span class="n">X</span><span class="o">]</span> <span class="o">[</span><span class="n">MetricSpace</span> <span class="n">Y</span><span class="o">]</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">→</span> <span class="n">Y</span><span class="o">}</span> <span class="o">(</span><span class="n">hf</span> <span class="o">:</span> <span class="n">Continuous</span> <span class="n">f</span><span class="o">)</span> <span class="o">:</span> <span class="n">Continuous</span> <span class="k">fun</span> <span class="n">p</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">×</span> <span class="n">X</span> <span class="bp">↦</span> <span class="n">dist</span> <span class="o">(</span><span class="n">f</span> <span class="n">p.1</span><span class="o">)</span> <span class="o">(</span><span class="n">f</span> <span class="n">p.2</span><span class="o">)</span> <span class="o">:=</span> <span class="n">hf.fst'.dist</span> <span class="n">hf.snd'</span> </pre></div> </div> <p>It’s your turn now to prove some continuity lemma. After trying the continuity tactic, you will need <code class="docutils literal notranslate"><span class="pre">Continuous.add</span></code>, <code class="docutils literal notranslate"><span class="pre">continuous_pow</span></code> and <code class="docutils literal notranslate"><span class="pre">continuous_id</span></code> to do it by hand.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Continuous</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Continuous</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">→</span> <span class="n">X</span><span class="o">}</span> <span class="o">(</span><span class="n">hf</span> <span class="o">:</span> <span class="n">Continuous</span> <span class="n">f</span><span class="o">)</span> <span class="o">:</span> <span class="n">Continuous</span> <span class="k">fun</span> <span class="n">x</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">↦</span> <span class="n">f</span> <span class="o">(</span><span class="n">x</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">+</span> <span class="n">x</span><span class="o">)</span> <span class="o">:=</span> <span class="gr">sorry</span> </pre></div> </div> <p>So far we saw continuity as a global notion, but one can also define continuity at a point.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">X</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">MetricSpace</span><span class="w"> </span><span class="n">X</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">MetricSpace</span><span class="w"> </span><span class="n">Y</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Y</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">ContinuousAt</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span><span class="o">,</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">δ</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span><span class="o">,</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="o">},</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">δ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Metric.continuousAt_iff</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">X</span> <span class="n">Y</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">MetricSpace</span> <span class="n">X</span><span class="o">]</span> <span class="o">[</span><span class="n">MetricSpace</span> <span class="n">Y</span><span class="o">]</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">→</span> <span class="n">Y</span><span class="o">)</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">X</span><span class="o">)</span> <span class="o">:</span> <span class="n">ContinuousAt</span> <span class="n">f</span> <span class="n">a</span> <span class="bp">↔</span> <span class="bp">∀</span> <span class="n">ε</span> <span class="bp">></span> <span class="mi">0</span><span class="o">,</span> <span class="bp">∃</span> <span class="n">δ</span> <span class="bp">></span> <span class="mi">0</span><span class="o">,</span> <span class="bp">∀</span> <span class="o">{</span><span class="n">x</span><span class="o">},</span> <span class="n">dist</span> <span class="n">x</span> <span class="n">a</span> <span class="bp"><</span> <span class="n">δ</span> <span class="bp">→</span> <span class="n">dist</span> <span class="o">(</span><span class="n">f</span> <span class="n">x</span><span class="o">)</span> <span class="o">(</span><span class="n">f</span> <span class="n">a</span><span class="o">)</span> <span class="bp"><</span> <span class="n">ε</span> <span class="o">:=</span> <span class="n">Metric.continuousAt_iff</span> </pre></div> </div> </section> <section id="balls-open-sets-and-closed-sets"> <h3><span class="section-number">10.2.2. </span>Balls, open sets and closed sets<a class="headerlink" href="#balls-open-sets-and-closed-sets" title="Link to this heading"></a></h3> <h3><span class="section-number">10.2.2. </span>Balls, open sets and closed sets<a class="headerlink" href="#balls-open-sets-and-closed-sets" title="Permalink to this heading"></a></h3> <p>Once we have a distance function, the most important geometric definitions are (open) balls and closed balls.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">r</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">(</span><span class="n">r</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Metric.ball</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="o">}</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">Metric.ball</span> <span class="n">a</span> <span class="n">r</span> <span class="bp">=</span> <span class="o">{</span> <span class="n">b</span> <span class="bp">|</span> <span class="n">dist</span> <span class="n">b</span> <span class="n">a</span> <span class="bp"><</span> <span class="n">r</span> <span class="o">}</span> <span class="o">:=</span> <span class="n">rfl</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Metric.closedBall</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="o">}</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">Metric.closedBall</span> <span class="n">a</span> <span class="n">r</span> <span class="bp">=</span> <span class="o">{</span> <span class="n">b</span> <span class="bp">|</span> <span class="n">dist</span> <span class="n">b</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">r</span> <span class="o">}</span> <span class="o">:=</span> <span class="n">rfl</span> </pre></div> </div> <p>Note that <cite>r</cite> is any real number here, there is no sign restriction. Of course some statements do require a radius condition.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">hr</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">r</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">Metric.ball</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Metric.mem_ball_self</span><span class="w"> </span><span class="n">hr</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">hr</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp"><</span> <span class="n">r</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">∈</span> <span class="n">Metric.ball</span> <span class="n">a</span> <span class="n">r</span> <span class="o">:=</span> <span class="n">Metric.mem_ball_self</span> <span class="n">hr</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">hr</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">r</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">Metric.closedBall</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Metric.mem_closedBall_self</span><span class="w"> </span><span class="n">hr</span> <span class="kd">example</span> <span class="o">(</span><span class="n">hr</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp">≤</span> <span class="n">r</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">∈</span> <span class="n">Metric.closedBall</span> <span class="n">a</span> <span class="n">r</span> <span class="o">:=</span> <span class="n">Metric.mem_closedBall_self</span> <span class="n">hr</span> </pre></div> </div> <p>Once we have balls, we can define open sets. They are actually defined in a more general setting covered in the next section, but we have lemmas recasting the definition in terms of balls.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">X</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">IsOpen</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span><span class="o">,</span><span class="w"> </span><span class="n">Metric.ball</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Metric.isOpen_iff</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">s</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">X</span><span class="o">)</span> <span class="o">:</span> <span class="n">IsOpen</span> <span class="n">s</span> <span class="bp">↔</span> <span class="bp">∀</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">s</span><span class="o">,</span> <span class="bp">∃</span> <span class="n">ε</span> <span class="bp">></span> <span class="mi">0</span><span class="o">,</span> <span class="n">Metric.ball</span> <span class="n">x</span> <span class="n">ε</span> <span class="bp">⊆</span> <span class="n">s</span> <span class="o">:=</span> <span class="n">Metric.isOpen_iff</span> </pre></div> </div> <p>Then closed sets are sets whose complement is open. Their important property is they are closed under limits. The closure of a set is the smallest closed set containing it.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">IsClosed</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">IsOpen</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="bp">ᶜ</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">isOpen_compl_iff.symm</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">s</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">X</span><span class="o">}</span> <span class="o">:</span> <span class="n">IsClosed</span> <span class="n">s</span> <span class="bp">↔</span> <span class="n">IsOpen</span> <span class="o">(</span><span class="n">s</span><span class="bp">ᶜ</span><span class="o">)</span> <span class="o">:=</span> <span class="n">isOpen_compl_iff.symm</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hs</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">IsClosed</span><span class="w"> </span><span class="n">s</span><span class="o">)</span><span class="w"> </span><span class="o">{</span><span class="n">u</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hu</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Tendsto</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="n">atTop</span><span class="w"> </span><span class="o">(</span><span class="n">𝓝</span><span class="w"> </span><span class="n">a</span><span class="o">))</span> <span class="w"> </span><span class="o">(</span><span class="n">hus</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">hs.mem_of_tendsto</span><span class="w"> </span><span class="n">hu</span><span class="w"> </span><span class="o">(</span><span class="n">Eventually.of_forall</span><span class="w"> </span><span class="n">hus</span><span class="o">)</span> <span class="kd">example</span> <span class="o">{</span><span class="n">s</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">X</span><span class="o">}</span> <span class="o">(</span><span class="n">hs</span> <span class="o">:</span> <span class="n">IsClosed</span> <span class="n">s</span><span class="o">)</span> <span class="o">{</span><span class="n">u</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">X</span><span class="o">}</span> <span class="o">(</span><span class="n">hu</span> <span class="o">:</span> <span class="n">Tendsto</span> <span class="n">u</span> <span class="n">atTop</span> <span class="o">(</span><span class="bp">𝓝</span> <span class="n">a</span><span class="o">))</span> <span class="o">(</span><span class="n">hus</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">n</span><span class="o">,</span> <span class="n">u</span> <span class="n">n</span> <span class="bp">∈</span> <span class="n">s</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">∈</span> <span class="n">s</span> <span class="o">:=</span> <span class="n">hs.mem_of_tendsto</span> <span class="n">hu</span> <span class="o">(</span><span class="n">Eventually.of_forall</span> <span class="n">hus</span><span class="o">)</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">closure</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span><span class="o">,</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">Metric.ball</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Metric.mem_closure_iff</span> <span class="kd">example</span> <span class="o">{</span><span class="n">s</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">X</span><span class="o">}</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">∈</span> <span class="n">closure</span> <span class="n">s</span> <span class="bp">↔</span> <span class="bp">∀</span> <span class="n">ε</span> <span class="bp">></span> <span class="mi">0</span><span class="o">,</span> <span class="bp">∃</span> <span class="n">b</span> <span class="bp">∈</span> <span class="n">s</span><span class="o">,</span> <span class="n">a</span> <span class="bp">∈</span> <span class="n">Metric.ball</span> <span class="n">b</span> <span class="n">ε</span> <span class="o">:=</span> <span class="n">Metric.mem_closure_iff</span> </pre></div> </div> <p>Do the next exercise without using <cite>mem_closure_iff_seq_limit</cite></p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">u</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hu</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Tendsto</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="n">atTop</span><span class="w"> </span><span class="o">(</span><span class="n">𝓝</span><span class="w"> </span><span class="n">a</span><span class="o">))</span><span class="w"> </span><span class="o">{</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hs</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">closure</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">u</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">X</span><span class="o">}</span> <span class="o">(</span><span class="n">hu</span> <span class="o">:</span> <span class="n">Tendsto</span> <span class="n">u</span> <span class="n">atTop</span> <span class="o">(</span><span class="bp">𝓝</span> <span class="n">a</span><span class="o">))</span> <span class="o">{</span><span class="n">s</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">X</span><span class="o">}</span> <span class="o">(</span><span class="n">hs</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">n</span><span class="o">,</span> <span class="n">u</span> <span class="n">n</span> <span class="bp">∈</span> <span class="n">s</span><span class="o">)</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">∈</span> <span class="n">closure</span> <span class="n">s</span> <span class="o">:=</span> <span class="gr">sorry</span> </pre></div> </div> <p>Remember from the filters sections that neighborhood filters play a big role in Mathlib.
-
@@ -683,16 +679,16 @@ In the metric space context, the crucial point is that balls provide bases for tThe main lemmas here are <code class="docutils literal notranslate"><span class="pre">Metric.nhds_basis_ball</span></code> and <code class="docutils literal notranslate"><span class="pre">Metric.nhds_basis_closedBall</span></code> that claim this for open and closed balls with positive radius. The center point is an implicit argument so we can invoke <code class="docutils literal notranslate"><span class="pre">Filter.HasBasis.mem_iff</span></code> as in the following example.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">𝓝</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span><span class="o">,</span><span class="w"> </span><span class="n">Metric.ball</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Metric.nhds_basis_ball.mem_iff</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">x</span> <span class="o">:</span> <span class="n">X</span><span class="o">}</span> <span class="o">{</span><span class="n">s</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">X</span><span class="o">}</span> <span class="o">:</span> <span class="n">s</span> <span class="bp">∈</span> <span class="bp">𝓝</span> <span class="n">x</span> <span class="bp">↔</span> <span class="bp">∃</span> <span class="n">ε</span> <span class="bp">></span> <span class="mi">0</span><span class="o">,</span> <span class="n">Metric.ball</span> <span class="n">x</span> <span class="n">ε</span> <span class="bp">⊆</span> <span class="n">s</span> <span class="o">:=</span> <span class="n">Metric.nhds_basis_ball.mem_iff</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">𝓝</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span><span class="o">,</span><span class="w"> </span><span class="n">Metric.closedBall</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Metric.nhds_basis_closedBall.mem_iff</span> <span class="kd">example</span> <span class="o">{</span><span class="n">x</span> <span class="o">:</span> <span class="n">X</span><span class="o">}</span> <span class="o">{</span><span class="n">s</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">X</span><span class="o">}</span> <span class="o">:</span> <span class="n">s</span> <span class="bp">∈</span> <span class="bp">𝓝</span> <span class="n">x</span> <span class="bp">↔</span> <span class="bp">∃</span> <span class="n">ε</span> <span class="bp">></span> <span class="mi">0</span><span class="o">,</span> <span class="n">Metric.closedBall</span> <span class="n">x</span> <span class="n">ε</span> <span class="bp">⊆</span> <span class="n">s</span> <span class="o">:=</span> <span class="n">Metric.nhds_basis_closedBall.mem_iff</span> </pre></div> </div> </section> <section id="compactness"> <h3><span class="section-number">10.2.3. </span>Compactness<a class="headerlink" href="#compactness" title="Link to this heading"></a></h3> <h3><span class="section-number">10.2.3. </span>Compactness<a class="headerlink" href="#compactness" title="Permalink to this heading"></a></h3> <p>Compactness is an important topological notion. It distinguishes subsets of a metric space that enjoy the same kind of properties as segments in reals compared to other intervals:</p> <ul class="simple">
-
@@ -706,43 +702,43 @@ claims for compact sets in general metric spaces. In the second statement we onlneed continuity on the given set so we will use <code class="docutils literal notranslate"><span class="pre">ContinuousOn</span></code> instead of <code class="docutils literal notranslate"><span class="pre">Continuous</span></code>, and we will give separate statements for the minimum and the maximum. Of course all these results are deduced from more general versions, some of which will be discussed in later sections.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">IsCompact</span><span class="w"> </span><span class="o">(</span><span class="n">Set.Icc</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">isCompact_Icc</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">IsCompact</span> <span class="o">(</span><span class="n">Set.Icc</span> <span class="mi">0</span> <span class="mi">1</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:=</span> <span class="n">isCompact_Icc</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hs</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">IsCompact</span><span class="w"> </span><span class="n">s</span><span class="o">)</span><span class="w"> </span><span class="o">{</span><span class="n">u</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hu</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℕ</span><span class="o">,</span><span class="w"> </span><span class="n">StrictMono</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">Tendsto</span><span class="w"> </span><span class="o">(</span><span class="n">u</span><span class="w"> </span><span class="bp">∘</span><span class="w"> </span><span class="n">φ</span><span class="o">)</span><span class="w"> </span><span class="n">atTop</span><span class="w"> </span><span class="o">(</span><span class="n">𝓝</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">hs.tendsto_subseq</span><span class="w"> </span><span class="n">hu</span> <span class="kd">example</span> <span class="o">{</span><span class="n">s</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">X</span><span class="o">}</span> <span class="o">(</span><span class="n">hs</span> <span class="o">:</span> <span class="n">IsCompact</span> <span class="n">s</span><span class="o">)</span> <span class="o">{</span><span class="n">u</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">X</span><span class="o">}</span> <span class="o">(</span><span class="n">hu</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">n</span><span class="o">,</span> <span class="n">u</span> <span class="n">n</span> <span class="bp">∈</span> <span class="n">s</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">a</span> <span class="bp">∈</span> <span class="n">s</span><span class="o">,</span> <span class="bp">∃</span> <span class="n">φ</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">ℕ</span><span class="o">,</span> <span class="n">StrictMono</span> <span class="n">φ</span> <span class="bp">∧</span> <span class="n">Tendsto</span> <span class="o">(</span><span class="n">u</span> <span class="bp">∘</span> <span class="n">φ</span><span class="o">)</span> <span class="n">atTop</span> <span class="o">(</span><span class="bp">𝓝</span> <span class="n">a</span><span class="o">)</span> <span class="o">:=</span> <span class="n">hs.tendsto_subseq</span> <span class="n">hu</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hs</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">IsCompact</span><span class="w"> </span><span class="n">s</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hs'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s.Nonempty</span><span class="o">)</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span> <span class="w"> </span><span class="o">(</span><span class="n">hfs</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ContinuousOn</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">s</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">hs.exists_isMinOn</span><span class="w"> </span><span class="n">hs'</span><span class="w"> </span><span class="n">hfs</span> <span class="kd">example</span> <span class="o">{</span><span class="n">s</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">X</span><span class="o">}</span> <span class="o">(</span><span class="n">hs</span> <span class="o">:</span> <span class="n">IsCompact</span> <span class="n">s</span><span class="o">)</span> <span class="o">(</span><span class="n">hs'</span> <span class="o">:</span> <span class="n">s.Nonempty</span><span class="o">)</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">hfs</span> <span class="o">:</span> <span class="n">ContinuousOn</span> <span class="n">f</span> <span class="n">s</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">s</span><span class="o">,</span> <span class="bp">∀</span> <span class="n">y</span> <span class="bp">∈</span> <span class="n">s</span><span class="o">,</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">≤</span> <span class="n">f</span> <span class="n">y</span> <span class="o">:=</span> <span class="n">hs.exists_isMinOn</span> <span class="n">hs'</span> <span class="n">hfs</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hs</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">IsCompact</span><span class="w"> </span><span class="n">s</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hs'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s.Nonempty</span><span class="o">)</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span> <span class="w"> </span><span class="o">(</span><span class="n">hfs</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ContinuousOn</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">s</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">hs.exists_isMaxOn</span><span class="w"> </span><span class="n">hs'</span><span class="w"> </span><span class="n">hfs</span> <span class="kd">example</span> <span class="o">{</span><span class="n">s</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">X</span><span class="o">}</span> <span class="o">(</span><span class="n">hs</span> <span class="o">:</span> <span class="n">IsCompact</span> <span class="n">s</span><span class="o">)</span> <span class="o">(</span><span class="n">hs'</span> <span class="o">:</span> <span class="n">s.Nonempty</span><span class="o">)</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">hfs</span> <span class="o">:</span> <span class="n">ContinuousOn</span> <span class="n">f</span> <span class="n">s</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">s</span><span class="o">,</span> <span class="bp">∀</span> <span class="n">y</span> <span class="bp">∈</span> <span class="n">s</span><span class="o">,</span> <span class="n">f</span> <span class="n">y</span> <span class="bp">≤</span> <span class="n">f</span> <span class="n">x</span> <span class="o">:=</span> <span class="n">hs.exists_isMaxOn</span> <span class="n">hs'</span> <span class="n">hfs</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hs</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">IsCompact</span><span class="w"> </span><span class="n">s</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">IsClosed</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">hs.isClosed</span> <span class="kd">example</span> <span class="o">{</span><span class="n">s</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">X</span><span class="o">}</span> <span class="o">(</span><span class="n">hs</span> <span class="o">:</span> <span class="n">IsCompact</span> <span class="n">s</span><span class="o">)</span> <span class="o">:</span> <span class="n">IsClosed</span> <span class="n">s</span> <span class="o">:=</span> <span class="n">hs.isClosed</span> </pre></div> </div> <p>We can also specify that a metric spaces is globally compact, using an extra <code class="docutils literal notranslate"><span class="pre">Prop</span></code>-valued type class:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">X</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">MetricSpace</span><span class="w"> </span><span class="n">X</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">CompactSpace</span><span class="w"> </span><span class="n">X</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">IsCompact</span><span class="w"> </span><span class="o">(</span><span class="n">univ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">X</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">isCompact_univ</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">X</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">MetricSpace</span> <span class="n">X</span><span class="o">]</span> <span class="o">[</span><span class="n">CompactSpace</span> <span class="n">X</span><span class="o">]</span> <span class="o">:</span> <span class="n">IsCompact</span> <span class="o">(</span><span class="n">univ</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">X</span><span class="o">)</span> <span class="o">:=</span> <span class="n">isCompact_univ</span> </pre></div> </div> <p>In a compact metric space any closed set is compact, this is <code class="docutils literal notranslate"><span class="pre">IsClosed.isCompact</span></code>.</p> </section> <section id="uniformly-continuous-functions"> <h3><span class="section-number">10.2.4. </span>Uniformly continuous functions<a class="headerlink" href="#uniformly-continuous-functions" title="Link to this heading"></a></h3> <h3><span class="section-number">10.2.4. </span>Uniformly continuous functions<a class="headerlink" href="#uniformly-continuous-functions" title="Permalink to this heading"></a></h3> <p>We now turn to uniformity notions on metric spaces : uniformly continuous functions, Cauchy sequences and completeness. Again those are defined in a more general context but we have lemmas in the metric name space to access their elementary definitions. We start with uniform continuity.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">X</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">MetricSpace</span><span class="w"> </span><span class="n">X</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">Y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">MetricSpace</span><span class="w"> </span><span class="n">Y</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Y</span><span class="o">}</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">UniformContinuous</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">↔</span> <span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span><span class="o">,</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">δ</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span><span class="o">,</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="o">},</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">δ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Metric.uniformContinuous_iff</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">X</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">MetricSpace</span> <span class="n">X</span><span class="o">]</span> <span class="o">{</span><span class="n">Y</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">MetricSpace</span> <span class="n">Y</span><span class="o">]</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">→</span> <span class="n">Y</span><span class="o">}</span> <span class="o">:</span> <span class="n">UniformContinuous</span> <span class="n">f</span> <span class="bp">↔</span> <span class="bp">∀</span> <span class="n">ε</span> <span class="bp">></span> <span class="mi">0</span><span class="o">,</span> <span class="bp">∃</span> <span class="n">δ</span> <span class="bp">></span> <span class="mi">0</span><span class="o">,</span> <span class="bp">∀</span> <span class="o">{</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">X</span><span class="o">},</span> <span class="n">dist</span> <span class="n">a</span> <span class="n">b</span> <span class="bp"><</span> <span class="n">δ</span> <span class="bp">→</span> <span class="n">dist</span> <span class="o">(</span><span class="n">f</span> <span class="n">a</span><span class="o">)</span> <span class="o">(</span><span class="n">f</span> <span class="n">b</span><span class="o">)</span> <span class="bp"><</span> <span class="n">ε</span> <span class="o">:=</span> <span class="n">Metric.uniformContinuous_iff</span> </pre></div> </div> <p>In order to practice manipulating all those definitions, we will prove that continuous
-
@@ -758,109 +754,109 @@ And <code class="docutils literal notranslate"><span class="pre">K</span></code>If <code class="docutils literal notranslate"><span class="pre">K</span></code> is empty then we are clearly done (we can set <code class="docutils literal notranslate"><span class="pre">δ</span> <span class="pre">=</span> <span class="pre">1</span></code> for instance). So let’s assume <code class="docutils literal notranslate"><span class="pre">K</span></code> is not empty, and use the extreme value theorem to choose <code class="docutils literal notranslate"><span class="pre">(x₀,</span> <span class="pre">x₁)</span></code> attaining the infimum of the distance function on <code class="docutils literal notranslate"><span class="pre">K</span></code>. We can then set <code class="docutils literal notranslate"><span class="pre">δ</span> <span class="pre">=</span> <span class="pre">dist</span> <span class="pre">x₀</span> <span class="pre">x₁</span></code> and check everything works.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">X</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">MetricSpace</span><span class="w"> </span><span class="n">X</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">CompactSpace</span><span class="w"> </span><span class="n">X</span><span class="o">]</span> <span class="w"> </span><span class="o">{</span><span class="n">Y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">MetricSpace</span><span class="w"> </span><span class="n">Y</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Y</span><span class="o">}</span> <span class="w"> </span><span class="o">(</span><span class="n">hf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Continuous</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">UniformContinuous</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">X</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">MetricSpace</span> <span class="n">X</span><span class="o">]</span> <span class="o">[</span><span class="n">CompactSpace</span> <span class="n">X</span><span class="o">]</span> <span class="o">{</span><span class="n">Y</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">MetricSpace</span> <span class="n">Y</span><span class="o">]</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">→</span> <span class="n">Y</span><span class="o">}</span> <span class="o">(</span><span class="n">hf</span> <span class="o">:</span> <span class="n">Continuous</span> <span class="n">f</span><span class="o">)</span> <span class="o">:</span> <span class="n">UniformContinuous</span> <span class="n">f</span> <span class="o">:=</span> <span class="gr">sorry</span> </pre></div> </div> </section> <section id="completeness"> <h3><span class="section-number">10.2.5. </span>Completeness<a class="headerlink" href="#completeness" title="Link to this heading"></a></h3> <h3><span class="section-number">10.2.5. </span>Completeness<a class="headerlink" href="#completeness" title="Permalink to this heading"></a></h3> <p>A Cauchy sequence in a metric space is a sequence whose terms get closer and closer to each other. There are a couple of equivalent ways to state that idea. In particular converging sequences are Cauchy. The converse is true only in so-called <em>complete</em> spaces.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">u</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">X</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">CauchySeq</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span><span class="o">,</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">,</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">≥</span><span class="w"> </span><span class="n">N</span><span class="o">,</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">≥</span><span class="w"> </span><span class="n">N</span><span class="o">,</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="o">(</span><span class="n">u</span><span class="w"> </span><span class="n">m</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">u</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Metric.cauchySeq_iff</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">u</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">X</span><span class="o">)</span> <span class="o">:</span> <span class="n">CauchySeq</span> <span class="n">u</span> <span class="bp">↔</span> <span class="bp">∀</span> <span class="n">ε</span> <span class="bp">></span> <span class="mi">0</span><span class="o">,</span> <span class="bp">∃</span> <span class="n">N</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">,</span> <span class="bp">∀</span> <span class="n">m</span> <span class="bp">≥</span> <span class="n">N</span><span class="o">,</span> <span class="bp">∀</span> <span class="n">n</span> <span class="bp">≥</span> <span class="n">N</span><span class="o">,</span> <span class="n">dist</span> <span class="o">(</span><span class="n">u</span> <span class="n">m</span><span class="o">)</span> <span class="o">(</span><span class="n">u</span> <span class="n">n</span><span class="o">)</span> <span class="bp"><</span> <span class="n">ε</span> <span class="o">:=</span> <span class="n">Metric.cauchySeq_iff</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">u</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">X</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">CauchySeq</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span><span class="o">,</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">,</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">≥</span><span class="w"> </span><span class="n">N</span><span class="o">,</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="o">(</span><span class="n">u</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">u</span><span class="w"> </span><span class="n">N</span><span class="o">)</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Metric.cauchySeq_iff'</span> <span class="kd">example</span> <span class="o">(</span><span class="n">u</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">X</span><span class="o">)</span> <span class="o">:</span> <span class="n">CauchySeq</span> <span class="n">u</span> <span class="bp">↔</span> <span class="bp">∀</span> <span class="n">ε</span> <span class="bp">></span> <span class="mi">0</span><span class="o">,</span> <span class="bp">∃</span> <span class="n">N</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">,</span> <span class="bp">∀</span> <span class="n">n</span> <span class="bp">≥</span> <span class="n">N</span><span class="o">,</span> <span class="n">dist</span> <span class="o">(</span><span class="n">u</span> <span class="n">n</span><span class="o">)</span> <span class="o">(</span><span class="n">u</span> <span class="n">N</span><span class="o">)</span> <span class="bp"><</span> <span class="n">ε</span> <span class="o">:=</span> <span class="n">Metric.cauchySeq_iff'</span> <span class="kd">example</span><span class="w"> </span><span class="o">[</span><span class="n">CompleteSpace</span><span class="w"> </span><span class="n">X</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">u</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">X</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hu</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">CauchySeq</span><span class="w"> </span><span class="n">u</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">Tendsto</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="n">atTop</span><span class="w"> </span><span class="o">(</span><span class="n">𝓝</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">cauchySeq_tendsto_of_complete</span><span class="w"> </span><span class="n">hu</span> <span class="kd">example</span> <span class="o">[</span><span class="n">CompleteSpace</span> <span class="n">X</span><span class="o">]</span> <span class="o">(</span><span class="n">u</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">X</span><span class="o">)</span> <span class="o">(</span><span class="n">hu</span> <span class="o">:</span> <span class="n">CauchySeq</span> <span class="n">u</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">x</span><span class="o">,</span> <span class="n">Tendsto</span> <span class="n">u</span> <span class="n">atTop</span> <span class="o">(</span><span class="bp">𝓝</span> <span class="n">x</span><span class="o">)</span> <span class="o">:=</span> <span class="n">cauchySeq_tendsto_of_complete</span> <span class="n">hu</span> </pre></div> </div> <p>We’ll practice using this definition by proving a convenient criterion which is a special case of a criterion appearing in Mathlib. This is also a good opportunity to practice using big sums in a geometric context. In addition to the explanations from the filters section, you will probably need <code class="docutils literal notranslate"><span class="pre">tendsto_pow_atTop_nhds_zero_of_lt_one</span></code>, <code class="docutils literal notranslate"><span class="pre">Tendsto.mul</span></code> and <code class="docutils literal notranslate"><span class="pre">dist_le_range_sum_dist</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">cauchySeq_of_le_geometric_two'</span><span class="w"> </span><span class="o">{</span><span class="n">u</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">X</span><span class="o">}</span> <span class="w"> </span><span class="o">(</span><span class="n">hu</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">,</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="o">(</span><span class="n">u</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">u</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="o">))</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="o">(</span><span class="mi">1</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">CauchySeq</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">Metric.cauchySeq_iff'</span><span class="o">]</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="n">ε_pos</span> <span class="w"> </span><span class="n">obtain</span><span class="w"> </span><span class="o">⟨</span><span class="n">N</span><span class="o">,</span><span class="w"> </span><span class="n">hN</span><span class="o">⟩</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">,</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">N</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">hn</span> <span class="w"> </span><span class="n">obtain</span><span class="w"> </span><span class="o">⟨</span><span class="n">k</span><span class="o">,</span><span class="w"> </span><span class="n">rfl</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">k</span><span class="o">⟩</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">le_iff_exists_add.mp</span><span class="w"> </span><span class="n">hn</span> <span class="w"> </span><span class="k">calc</span> <span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="o">(</span><span class="n">u</span><span class="w"> </span><span class="o">(</span><span class="n">N</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">k</span><span class="o">))</span><span class="w"> </span><span class="o">(</span><span class="n">u</span><span class="w"> </span><span class="n">N</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="o">(</span><span class="n">u</span><span class="w"> </span><span class="o">(</span><span class="n">N</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">0</span><span class="o">))</span><span class="w"> </span><span class="o">(</span><span class="n">u</span><span class="w"> </span><span class="o">(</span><span class="n">N</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">k</span><span class="o">))</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="bp">∑</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">range</span><span class="w"> </span><span class="n">k</span><span class="o">,</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="o">(</span><span class="n">u</span><span class="w"> </span><span class="o">(</span><span class="n">N</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">i</span><span class="o">))</span><span class="w"> </span><span class="o">(</span><span class="n">u</span><span class="w"> </span><span class="o">(</span><span class="n">N</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="o">(</span><span class="n">i</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="o">)))</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="bp">∑</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">range</span><span class="w"> </span><span class="n">k</span><span class="o">,</span><span class="w"> </span><span class="o">(</span><span class="mi">1</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="o">(</span><span class="n">N</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="bp">∑</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">range</span><span class="w"> </span><span class="n">k</span><span class="o">,</span><span class="w"> </span><span class="o">(</span><span class="mi">1</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="n">N</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">cauchySeq_of_le_geometric_two'</span> <span class="o">{</span><span class="n">u</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">X</span><span class="o">}</span> <span class="o">(</span><span class="n">hu</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">,</span> <span class="n">dist</span> <span class="o">(</span><span class="n">u</span> <span class="n">n</span><span class="o">)</span> <span class="o">(</span><span class="n">u</span> <span class="o">(</span><span class="n">n</span> <span class="bp">+</span> <span class="mi">1</span><span class="o">))</span> <span class="bp">≤</span> <span class="o">(</span><span class="mi">1</span> <span class="bp">/</span> <span class="mi">2</span><span class="o">)</span> <span class="bp">^</span> <span class="n">n</span><span class="o">)</span> <span class="o">:</span> <span class="n">CauchySeq</span> <span class="n">u</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">Metric.cauchySeq_iff'</span><span class="o">]</span> <span class="n">intro</span> <span class="n">ε</span> <span class="n">ε_pos</span> <span class="n">obtain</span> <span class="o">⟨</span><span class="n">N</span><span class="o">,</span> <span class="n">hN</span><span class="o">⟩</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">N</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">,</span> <span class="mi">1</span> <span class="bp">/</span> <span class="mi">2</span> <span class="bp">^</span> <span class="n">N</span> <span class="bp">*</span> <span class="mi">2</span> <span class="bp"><</span> <span class="n">ε</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="n">use</span> <span class="n">N</span> <span class="n">intro</span> <span class="n">n</span> <span class="n">hn</span> <span class="n">obtain</span> <span class="o">⟨</span><span class="n">k</span><span class="o">,</span> <span class="n">rfl</span> <span class="o">:</span> <span class="n">n</span> <span class="bp">=</span> <span class="n">N</span> <span class="bp">+</span> <span class="n">k</span><span class="o">⟩</span> <span class="o">:=</span> <span class="n">le_iff_exists_add.mp</span> <span class="n">hn</span> <span class="k">calc</span> <span class="n">dist</span> <span class="o">(</span><span class="n">u</span> <span class="o">(</span><span class="n">N</span> <span class="bp">+</span> <span class="n">k</span><span class="o">))</span> <span class="o">(</span><span class="n">u</span> <span class="n">N</span><span class="o">)</span> <span class="bp">=</span> <span class="n">dist</span> <span class="o">(</span><span class="n">u</span> <span class="o">(</span><span class="n">N</span> <span class="bp">+</span> <span class="mi">0</span><span class="o">))</span> <span class="o">(</span><span class="n">u</span> <span class="o">(</span><span class="n">N</span> <span class="bp">+</span> <span class="n">k</span><span class="o">))</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="n">_</span> <span class="bp">≤</span> <span class="bp">∑</span> <span class="n">i</span> <span class="k">in</span> <span class="n">range</span> <span class="n">k</span><span class="o">,</span> <span class="n">dist</span> <span class="o">(</span><span class="n">u</span> <span class="o">(</span><span class="n">N</span> <span class="bp">+</span> <span class="n">i</span><span class="o">))</span> <span class="o">(</span><span class="n">u</span> <span class="o">(</span><span class="n">N</span> <span class="bp">+</span> <span class="o">(</span><span class="n">i</span> <span class="bp">+</span> <span class="mi">1</span><span class="o">)))</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="n">_</span> <span class="bp">≤</span> <span class="bp">∑</span> <span class="n">i</span> <span class="k">in</span> <span class="n">range</span> <span class="n">k</span><span class="o">,</span> <span class="o">(</span><span class="mi">1</span> <span class="bp">/</span> <span class="mi">2</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="bp">^</span> <span class="o">(</span><span class="n">N</span> <span class="bp">+</span> <span class="n">i</span><span class="o">)</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="n">_</span> <span class="bp">=</span> <span class="mi">1</span> <span class="bp">/</span> <span class="mi">2</span> <span class="bp">^</span> <span class="n">N</span> <span class="bp">*</span> <span class="bp">∑</span> <span class="n">i</span> <span class="k">in</span> <span class="n">range</span> <span class="n">k</span><span class="o">,</span> <span class="o">(</span><span class="mi">1</span> <span class="bp">/</span> <span class="mi">2</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="bp">^</span> <span class="n">i</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="n">_</span> <span class="bp">≤</span> <span class="mi">1</span> <span class="bp">/</span> <span class="mi">2</span> <span class="bp">^</span> <span class="n">N</span> <span class="bp">*</span> <span class="mi">2</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="n">_</span> <span class="bp"><</span> <span class="n">ε</span> <span class="o">:=</span> <span class="gr">sorry</span> </pre></div> </div> <p>We are ready for the final boss of this section: Baire’s theorem for complete metric spaces! The proof skeleton below shows interesting techniques. It uses the <code class="docutils literal notranslate"><span class="pre">choose</span></code> tactic in its exclamation mark variant (you should experiment with removing this exclamation mark) and it shows how to define something inductively in the middle of a proof using <code class="docutils literal notranslate"><span class="pre">Nat.rec_on</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span><span class="w"> </span><span class="n">Metric</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span> <span class="n">Metric</span> <span class="kd">example</span><span class="w"> </span><span class="o">[</span><span class="n">CompleteSpace</span><span class="w"> </span><span class="n">X</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">X</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">ho</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="n">IsOpen</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">n</span><span class="o">))</span><span class="w"> </span><span class="o">(</span><span class="n">hd</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="n">Dense</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">n</span><span class="o">))</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">Dense</span><span class="w"> </span><span class="o">(</span><span class="bp">⋂</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="k">let</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="o">(</span><span class="mi">1</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="n">n</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">Bpos</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="n">n</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="c">/-</span><span class="cm"> Translate the density assumption into two functions `center` and `radius` associating</span> <span class="kd">example</span> <span class="o">[</span><span class="n">CompleteSpace</span> <span class="n">X</span><span class="o">]</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">Set</span> <span class="n">X</span><span class="o">)</span> <span class="o">(</span><span class="n">ho</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">n</span><span class="o">,</span> <span class="n">IsOpen</span> <span class="o">(</span><span class="n">f</span> <span class="n">n</span><span class="o">))</span> <span class="o">(</span><span class="n">hd</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">n</span><span class="o">,</span> <span class="n">Dense</span> <span class="o">(</span><span class="n">f</span> <span class="n">n</span><span class="o">))</span> <span class="o">:</span> <span class="n">Dense</span> <span class="o">(</span><span class="bp">⋂</span> <span class="n">n</span><span class="o">,</span> <span class="n">f</span> <span class="n">n</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="k">let</span> <span class="n">B</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">ℝ</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">n</span> <span class="bp">↦</span> <span class="o">(</span><span class="mi">1</span> <span class="bp">/</span> <span class="mi">2</span><span class="o">)</span> <span class="bp">^</span> <span class="n">n</span> <span class="k">have</span> <span class="n">Bpos</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">n</span><span class="o">,</span> <span class="mi">0</span> <span class="bp"><</span> <span class="n">B</span> <span class="n">n</span> <span class="gr">sorry</span> <span class="c">/-</span><span class="cm"> Translate the density assumption into two functions `center` and `radius` associating</span> <span class="cm"> to any n, x, δ, δpos a center and a positive radius such that</span> <span class="cm"> `closedBall center radius` is included both in `f n` and in `closedBall x δ`.</span> <span class="cm"> We can also require `radius ≤ (1/2)^(n+1)`, to ensure we get a Cauchy sequence later. -/</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="o">),</span> <span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">δ</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span><span class="o">,</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="o">,</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span><span class="o">,</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="o">)</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">closedBall</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">closedBall</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">δ</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">choose</span><span class="bp">!</span><span class="w"> </span><span class="n">center</span><span class="w"> </span><span class="n">radius</span><span class="w"> </span><span class="n">Hpos</span><span class="w"> </span><span class="n">HB</span><span class="w"> </span><span class="n">Hball</span><span class="w"> </span><span class="n">using</span><span class="w"> </span><span class="n">this</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">x</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">mem_closure_iff_nhds_basis</span><span class="w"> </span><span class="n">nhds_basis_closedBall</span><span class="o">]</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="n">εpos</span> <span class="w"> </span><span class="c">/-</span><span class="cm"> `ε` is positive. We have to find a point in the ball of radius `ε` around `x`</span> <span class="k">have</span> <span class="o">:</span> <span class="bp">∀</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">X</span><span class="o">),</span> <span class="bp">∀</span> <span class="n">δ</span> <span class="bp">></span> <span class="mi">0</span><span class="o">,</span> <span class="bp">∃</span> <span class="n">y</span> <span class="o">:</span> <span class="n">X</span><span class="o">,</span> <span class="bp">∃</span> <span class="n">r</span> <span class="bp">></span> <span class="mi">0</span><span class="o">,</span> <span class="n">r</span> <span class="bp">≤</span> <span class="n">B</span> <span class="o">(</span><span class="n">n</span> <span class="bp">+</span> <span class="mi">1</span><span class="o">)</span> <span class="bp">∧</span> <span class="n">closedBall</span> <span class="n">y</span> <span class="n">r</span> <span class="bp">⊆</span> <span class="n">closedBall</span> <span class="n">x</span> <span class="n">δ</span> <span class="bp">∩</span> <span class="n">f</span> <span class="n">n</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="n">choose</span><span class="bp">!</span> <span class="n">center</span> <span class="n">radius</span> <span class="n">Hpos</span> <span class="n">HB</span> <span class="n">Hball</span> <span class="n">using</span> <span class="n">this</span> <span class="n">intro</span> <span class="n">x</span> <span class="n">rw</span> <span class="o">[</span><span class="n">mem_closure_iff_nhds_basis</span> <span class="n">nhds_basis_closedBall</span><span class="o">]</span> <span class="n">intro</span> <span class="n">ε</span> <span class="n">εpos</span> <span class="c">/-</span><span class="cm"> `ε` is positive. We have to find a point in the ball of radius `ε` around `x`</span> <span class="cm"> belonging to all `f n`. For this, we construct inductively a sequence</span> <span class="cm"> `F n = (c n, r n)` such that the closed ball `closedBall (c n) (r n)` is included</span> <span class="cm"> in the previous ball and in `f n`, and such that `r n` is small enough to ensure</span> <span class="cm"> that `c n` is a Cauchy sequence. Then `c n` converges to a limit which belongs</span> <span class="cm"> to all the `f n`. -/</span> <span class="w"> </span><span class="k">let</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">×</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">↦</span> <span class="w"> </span><span class="n">Nat.recOn</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">(</span><span class="n">Prod.mk</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">(</span><span class="n">min</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="o">(</span><span class="n">B</span><span class="w"> </span><span class="mi">0</span><span class="o">)))</span> <span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">Prod.mk</span><span class="w"> </span><span class="o">(</span><span class="n">center</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">p</span><span class="bp">.</span><span class="mi">1</span><span class="w"> </span><span class="n">p</span><span class="bp">.</span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">radius</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">p</span><span class="bp">.</span><span class="mi">1</span><span class="w"> </span><span class="n">p</span><span class="bp">.</span><span class="mi">2</span><span class="o">)</span> <span class="w"> </span><span class="k">let</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="o">(</span><span class="n">F</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="bp">.</span><span class="mi">1</span> <span class="w"> </span><span class="k">let</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="o">(</span><span class="n">F</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="bp">.</span><span class="mi">2</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">rpos</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">rB</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="n">r</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">incl</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="n">closedBall</span><span class="w"> </span><span class="o">(</span><span class="n">c</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="o">))</span><span class="w"> </span><span class="o">(</span><span class="n">r</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="o">))</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">closedBall</span><span class="w"> </span><span class="o">(</span><span class="n">c</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">r</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="bp">∩</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">cdist</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="n">dist</span><span class="w"> </span><span class="o">(</span><span class="n">c</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">c</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="mi">1</span><span class="o">))</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">CauchySeq</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">cauchySeq_of_le_geometric_two'</span><span class="w"> </span><span class="n">cdist</span> <span class="w"> </span><span class="c1">-- as the sequence `c n` is Cauchy in a complete space, it converges to a limit `y`.</span> <span class="w"> </span><span class="n">rcases</span><span class="w"> </span><span class="n">cauchySeq_tendsto_of_complete</span><span class="w"> </span><span class="n">this</span><span class="w"> </span><span class="k">with</span><span class="w"> </span><span class="o">⟨</span><span class="n">y</span><span class="o">,</span><span class="w"> </span><span class="n">ylim</span><span class="o">⟩</span> <span class="w"> </span><span class="c1">-- this point `y` will be the desired point. We will check that it belongs to all</span> <span class="w"> </span><span class="c1">-- `f n` and to `ball x ε`.</span> <span class="w"> </span><span class="n">use</span><span class="w"> </span><span class="n">y</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">I</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="bp">≥</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="n">closedBall</span><span class="w"> </span><span class="o">(</span><span class="n">c</span><span class="w"> </span><span class="n">m</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">r</span><span class="w"> </span><span class="n">m</span><span class="o">)</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">closedBall</span><span class="w"> </span><span class="o">(</span><span class="n">c</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">r</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">yball</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">closedBall</span><span class="w"> </span><span class="o">(</span><span class="n">c</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">r</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="gr">sorry</span> <span class="k">let</span> <span class="n">F</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">X</span> <span class="bp">×</span> <span class="n">ℝ</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">n</span> <span class="bp">↦</span> <span class="n">Nat.recOn</span> <span class="n">n</span> <span class="o">(</span><span class="n">Prod.mk</span> <span class="n">x</span> <span class="o">(</span><span class="n">min</span> <span class="n">ε</span> <span class="o">(</span><span class="n">B</span> <span class="mi">0</span><span class="o">)))</span> <span class="k">fun</span> <span class="n">n</span> <span class="n">p</span> <span class="bp">↦</span> <span class="n">Prod.mk</span> <span class="o">(</span><span class="n">center</span> <span class="n">n</span> <span class="n">p.1</span> <span class="n">p.2</span><span class="o">)</span> <span class="o">(</span><span class="n">radius</span> <span class="n">n</span> <span class="n">p.1</span> <span class="n">p.2</span><span class="o">)</span> <span class="k">let</span> <span class="n">c</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">X</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">n</span> <span class="bp">↦</span> <span class="o">(</span><span class="n">F</span> <span class="n">n</span><span class="o">)</span><span class="bp">.</span><span class="mi">1</span> <span class="k">let</span> <span class="n">r</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">ℝ</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">n</span> <span class="bp">↦</span> <span class="o">(</span><span class="n">F</span> <span class="n">n</span><span class="o">)</span><span class="bp">.</span><span class="mi">2</span> <span class="k">have</span> <span class="n">rpos</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">n</span><span class="o">,</span> <span class="mi">0</span> <span class="bp"><</span> <span class="n">r</span> <span class="n">n</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="k">have</span> <span class="n">rB</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">n</span><span class="o">,</span> <span class="n">r</span> <span class="n">n</span> <span class="bp">≤</span> <span class="n">B</span> <span class="n">n</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="k">have</span> <span class="n">incl</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">n</span><span class="o">,</span> <span class="n">closedBall</span> <span class="o">(</span><span class="n">c</span> <span class="o">(</span><span class="n">n</span> <span class="bp">+</span> <span class="mi">1</span><span class="o">))</span> <span class="o">(</span><span class="n">r</span> <span class="o">(</span><span class="n">n</span> <span class="bp">+</span> <span class="mi">1</span><span class="o">))</span> <span class="bp">⊆</span> <span class="n">closedBall</span> <span class="o">(</span><span class="n">c</span> <span class="n">n</span><span class="o">)</span> <span class="o">(</span><span class="n">r</span> <span class="n">n</span><span class="o">)</span> <span class="bp">∩</span> <span class="n">f</span> <span class="n">n</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="k">have</span> <span class="n">cdist</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">n</span><span class="o">,</span> <span class="n">dist</span> <span class="o">(</span><span class="n">c</span> <span class="n">n</span><span class="o">)</span> <span class="o">(</span><span class="n">c</span> <span class="o">(</span><span class="n">n</span> <span class="bp">+</span> <span class="mi">1</span><span class="o">))</span> <span class="bp">≤</span> <span class="n">B</span> <span class="n">n</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="k">have</span> <span class="o">:</span> <span class="n">CauchySeq</span> <span class="n">c</span> <span class="o">:=</span> <span class="n">cauchySeq_of_le_geometric_two'</span> <span class="n">cdist</span> <span class="c1">-- as the sequence `c n` is Cauchy in a complete space, it converges to a limit `y`.</span> <span class="n">rcases</span> <span class="n">cauchySeq_tendsto_of_complete</span> <span class="n">this</span> <span class="k">with</span> <span class="o">⟨</span><span class="n">y</span><span class="o">,</span> <span class="n">ylim</span><span class="o">⟩</span> <span class="c1">-- this point `y` will be the desired point. We will check that it belongs to all</span> <span class="c1">-- `f n` and to `ball x ε`.</span> <span class="n">use</span> <span class="n">y</span> <span class="k">have</span> <span class="n">I</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">n</span><span class="o">,</span> <span class="bp">∀</span> <span class="n">m</span> <span class="bp">≥</span> <span class="n">n</span><span class="o">,</span> <span class="n">closedBall</span> <span class="o">(</span><span class="n">c</span> <span class="n">m</span><span class="o">)</span> <span class="o">(</span><span class="n">r</span> <span class="n">m</span><span class="o">)</span> <span class="bp">⊆</span> <span class="n">closedBall</span> <span class="o">(</span><span class="n">c</span> <span class="n">n</span><span class="o">)</span> <span class="o">(</span><span class="n">r</span> <span class="n">n</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="k">have</span> <span class="n">yball</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">n</span><span class="o">,</span> <span class="n">y</span> <span class="bp">∈</span> <span class="n">closedBall</span> <span class="o">(</span><span class="n">c</span> <span class="n">n</span><span class="o">)</span> <span class="o">(</span><span class="n">r</span> <span class="n">n</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="gr">sorry</span> </pre></div> </div> </section> </section> <section id="topological-spaces"> <span id="index-4"></span><span id="id4"></span><h2><span class="section-number">10.3. </span>Topological spaces<a class="headerlink" href="#topological-spaces" title="Link to this heading"></a></h2> <span id="index-4"></span><span id="id4"></span><h2><span class="section-number">10.3. </span>Topological spaces<a class="headerlink" href="#topological-spaces" title="Permalink to this heading"></a></h2> <section id="fundamentals"> <h3><span class="section-number">10.3.1. </span>Fundamentals<a class="headerlink" href="#fundamentals" title="Link to this heading"></a></h3> <h3><span class="section-number">10.3.1. </span>Fundamentals<a class="headerlink" href="#fundamentals" title="Permalink to this heading"></a></h3> <p>We now go up in generality and introduce topological spaces. We will review the two main ways to define topological spaces and then explain how the category of topological spaces is much better behaved than the category of metric spaces. Note that we won’t be using Mathlib category theory here, only having
-
@@ -870,28 +866,28 @@ remember the notion of open sets (or equivalently the notion of closed sets). Fra topological space is a type equipped with a collection of sets that are called open sets. This collection has to satisfy a number of axioms presented below (this collection is slightly redundant but we will ignore that).</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">section</span> <span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">X</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">TopologicalSpace</span><span class="w"> </span><span class="n">X</span><span class="o">]</span> <span class="kd">variable</span> <span class="o">{</span><span class="n">X</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">TopologicalSpace</span> <span class="n">X</span><span class="o">]</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">IsOpen</span><span class="w"> </span><span class="o">(</span><span class="n">univ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">X</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">isOpen_univ</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">IsOpen</span> <span class="o">(</span><span class="n">univ</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">X</span><span class="o">)</span> <span class="o">:=</span> <span class="n">isOpen_univ</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">IsOpen</span><span class="w"> </span><span class="o">(</span><span class="bp">∅</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">X</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">isOpen_empty</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">IsOpen</span> <span class="o">(</span><span class="bp">∅</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">X</span><span class="o">)</span> <span class="o">:=</span> <span class="n">isOpen_empty</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">ι</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hs</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">IsOpen</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="n">i</span><span class="o">))</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">IsOpen</span><span class="w"> </span><span class="o">(</span><span class="bp">⋃</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">isOpen_iUnion</span><span class="w"> </span><span class="n">hs</span> <span class="kd">example</span> <span class="o">{</span><span class="n">ι</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">{</span><span class="n">s</span> <span class="o">:</span> <span class="n">ι</span> <span class="bp">→</span> <span class="n">Set</span> <span class="n">X</span><span class="o">}</span> <span class="o">(</span><span class="n">hs</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">i</span><span class="o">,</span> <span class="n">IsOpen</span> <span class="o">(</span><span class="n">s</span> <span class="n">i</span><span class="o">))</span> <span class="o">:</span> <span class="n">IsOpen</span> <span class="o">(</span><span class="bp">⋃</span> <span class="n">i</span><span class="o">,</span> <span class="n">s</span> <span class="n">i</span><span class="o">)</span> <span class="o">:=</span> <span class="n">isOpen_iUnion</span> <span class="n">hs</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">ι</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Fintype</span><span class="w"> </span><span class="n">ι</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hs</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">IsOpen</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="n">i</span><span class="o">))</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">IsOpen</span><span class="w"> </span><span class="o">(</span><span class="bp">⋂</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">isOpen_iInter_of_finite</span><span class="w"> </span><span class="n">hs</span> <span class="kd">example</span> <span class="o">{</span><span class="n">ι</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Fintype</span> <span class="n">ι</span><span class="o">]</span> <span class="o">{</span><span class="n">s</span> <span class="o">:</span> <span class="n">ι</span> <span class="bp">→</span> <span class="n">Set</span> <span class="n">X</span><span class="o">}</span> <span class="o">(</span><span class="n">hs</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">i</span><span class="o">,</span> <span class="n">IsOpen</span> <span class="o">(</span><span class="n">s</span> <span class="n">i</span><span class="o">))</span> <span class="o">:</span> <span class="n">IsOpen</span> <span class="o">(</span><span class="bp">⋂</span> <span class="n">i</span><span class="o">,</span> <span class="n">s</span> <span class="n">i</span><span class="o">)</span> <span class="o">:=</span> <span class="n">isOpen_iInter_of_finite</span> <span class="n">hs</span> </pre></div> </div> <p>Closed sets are then defined as sets whose complement is open. A function between topological spaces <p>Closed sets are then defined as sets whose complement is open. A function between topological spaces is (globally) continuous if all preimages of open sets are open.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">Y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">TopologicalSpace</span><span class="w"> </span><span class="n">Y</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">Y</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">TopologicalSpace</span> <span class="n">Y</span><span class="o">]</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Y</span><span class="o">}</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Continuous</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="n">IsOpen</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">IsOpen</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="bp">⁻¹'</span><span class="w"> </span><span class="n">s</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">continuous_def</span> <span class="kd">example</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">→</span> <span class="n">Y</span><span class="o">}</span> <span class="o">:</span> <span class="n">Continuous</span> <span class="n">f</span> <span class="bp">↔</span> <span class="bp">∀</span> <span class="n">s</span><span class="o">,</span> <span class="n">IsOpen</span> <span class="n">s</span> <span class="bp">→</span> <span class="n">IsOpen</span> <span class="o">(</span><span class="n">f</span> <span class="bp">⁻¹'</span> <span class="n">s</span><span class="o">)</span> <span class="o">:=</span> <span class="n">continuous_def</span> </pre></div> </div> <p>With this definition we already see that, compared to metric spaces, topological spaces only remember
-
@@ -909,22 +905,22 @@ that <code class="docutils literal notranslate"><span class="pre">f</span> <span<code class="docutils literal notranslate"><span class="pre">f</span></code> of the generalized set of points that are close to <code class="docutils literal notranslate"><span class="pre">x</span></code> is contained in the generalized set of points that are close to <code class="docutils literal notranslate"><span class="pre">f</span> <span class="pre">x</span></code>. Recall this is spelled either <code class="docutils literal notranslate"><span class="pre">map</span> <span class="pre">f</span> <span class="pre">(𝓝</span> <span class="pre">x)</span> <span class="pre">≤</span> <span class="pre">𝓝</span> <span class="pre">(f</span> <span class="pre">x)</span></code> or <code class="docutils literal notranslate"><span class="pre">Tendsto</span> <span class="pre">f</span> <span class="pre">(𝓝</span> <span class="pre">x)</span> <span class="pre">(𝓝</span> <span class="pre">(f</span> <span class="pre">x))</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Y</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ContinuousAt</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">map</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">𝓝</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">𝓝</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Iff.rfl</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">→</span> <span class="n">Y</span><span class="o">}</span> <span class="o">{</span><span class="n">x</span> <span class="o">:</span> <span class="n">X</span><span class="o">}</span> <span class="o">:</span> <span class="n">ContinuousAt</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">↔</span> <span class="n">map</span> <span class="n">f</span> <span class="o">(</span><span class="bp">𝓝</span> <span class="n">x</span><span class="o">)</span> <span class="bp">≤</span> <span class="bp">𝓝</span> <span class="o">(</span><span class="n">f</span> <span class="n">x</span><span class="o">)</span> <span class="o">:=</span> <span class="n">Iff.rfl</span> </pre></div> </div> <p>One can also spell it using both neighborhoods seen as ordinary sets and a neighborhood filter seen as a generalized set: “for any neighborhood <code class="docutils literal notranslate"><span class="pre">U</span></code> of <code class="docutils literal notranslate"><span class="pre">f</span> <span class="pre">x</span></code>, all points close to <code class="docutils literal notranslate"><span class="pre">x</span></code> are sent to <code class="docutils literal notranslate"><span class="pre">U</span></code>”. Note that the proof is again <code class="docutils literal notranslate"><span class="pre">iff.rfl</span></code>, this point of view is definitionally equivalent to the previous one.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Y</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ContinuousAt</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">U</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">𝓝</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="o">),</span><span class="w"> </span><span class="bp">∀ᶠ</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">𝓝</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">U</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Iff.rfl</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">→</span> <span class="n">Y</span><span class="o">}</span> <span class="o">{</span><span class="n">x</span> <span class="o">:</span> <span class="n">X</span><span class="o">}</span> <span class="o">:</span> <span class="n">ContinuousAt</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">↔</span> <span class="bp">∀</span> <span class="n">U</span> <span class="bp">∈</span> <span class="bp">𝓝</span> <span class="o">(</span><span class="n">f</span> <span class="n">x</span><span class="o">),</span> <span class="bp">∀ᶠ</span> <span class="n">x</span> <span class="k">in</span> <span class="bp">𝓝</span> <span class="n">x</span><span class="o">,</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">U</span> <span class="o">:=</span> <span class="n">Iff.rfl</span> </pre></div> </div> <p>We now explain how to go from one point of view to the other. In terms of open sets, we can simply define members of <code class="docutils literal notranslate"><span class="pre">𝓝</span> <span class="pre">x</span></code> as sets that contain an open set containing <code class="docutils literal notranslate"><span class="pre">x</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">𝓝</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">t</span><span class="o">,</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">IsOpen</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">mem_nhds_iff</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">x</span> <span class="o">:</span> <span class="n">X</span><span class="o">}</span> <span class="o">{</span><span class="n">s</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">X</span><span class="o">}</span> <span class="o">:</span> <span class="n">s</span> <span class="bp">∈</span> <span class="bp">𝓝</span> <span class="n">x</span> <span class="bp">↔</span> <span class="bp">∃</span> <span class="n">t</span><span class="o">,</span> <span class="n">t</span> <span class="bp">⊆</span> <span class="n">s</span> <span class="bp">∧</span> <span class="n">IsOpen</span> <span class="n">t</span> <span class="bp">∧</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">t</span> <span class="o">:=</span> <span class="n">mem_nhds_iff</span> </pre></div> </div> <p>To go in the other direction we need to discuss the condition that <code class="docutils literal notranslate"><span class="pre">𝓝</span> <span class="pre">:</span> <span class="pre">X</span> <span class="pre">→</span> <span class="pre">Filter</span> <span class="pre">X</span></code> must satisfy
-
@@ -932,17 +928,17 @@ in order to be the neighborhood function of a topology.</p><p>The first constraint is that <code class="docutils literal notranslate"><span class="pre">𝓝</span> <span class="pre">x</span></code>, seen as a generalized set, contains the set <code class="docutils literal notranslate"><span class="pre">{x}</span></code> seen as the generalized set <code class="docutils literal notranslate"><span class="pre">pure</span> <span class="pre">x</span></code> (explaining this weird name would be too much of a digression, so we simply accept it for now). Another way to say it is that if a predicate holds for points close to <code class="docutils literal notranslate"><span class="pre">x</span></code> then it holds at <code class="docutils literal notranslate"><span class="pre">x</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">pure</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">𝓝</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">pure_le_nhds</span><span class="w"> </span><span class="n">x</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">X</span><span class="o">)</span> <span class="o">:</span> <span class="n">pure</span> <span class="n">x</span> <span class="bp">≤</span> <span class="bp">𝓝</span> <span class="n">x</span> <span class="o">:=</span> <span class="n">pure_le_nhds</span> <span class="n">x</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">P</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="kt">Prop</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀ᶠ</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">𝓝</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">h.self_of_nhds</span> <span class="kd">example</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">X</span><span class="o">)</span> <span class="o">(</span><span class="n">P</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">→</span> <span class="kt">Prop</span><span class="o">)</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="bp">∀ᶠ</span> <span class="n">y</span> <span class="k">in</span> <span class="bp">𝓝</span> <span class="n">x</span><span class="o">,</span> <span class="n">P</span> <span class="n">y</span><span class="o">)</span> <span class="o">:</span> <span class="n">P</span> <span class="n">x</span> <span class="o">:=</span> <span class="n">h.self_of_nhds</span> </pre></div> </div> <p>Then a more subtle requirement is that, for any predicate <code class="docutils literal notranslate"><span class="pre">P</span> <span class="pre">:</span> <span class="pre">X</span> <span class="pre">→</span> <span class="pre">Prop</span></code> and any <code class="docutils literal notranslate"><span class="pre">x</span></code>, if <code class="docutils literal notranslate"><span class="pre">P</span> <span class="pre">y</span></code> holds for <code class="docutils literal notranslate"><span class="pre">y</span></code> close to <code class="docutils literal notranslate"><span class="pre">x</span></code> then for <code class="docutils literal notranslate"><span class="pre">y</span></code> close to <code class="docutils literal notranslate"><span class="pre">x</span></code> and <code class="docutils literal notranslate"><span class="pre">z</span></code> close to <code class="docutils literal notranslate"><span class="pre">y</span></code>, <code class="docutils literal notranslate"><span class="pre">P</span> <span class="pre">z</span></code> holds. More precisely we have:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">P</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="kt">Prop</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀ᶠ</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">𝓝</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀ᶠ</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">𝓝</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="bp">∀ᶠ</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">𝓝</span><span class="w"> </span><span class="n">y</span><span class="o">,</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">eventually_eventually_nhds.mpr</span><span class="w"> </span><span class="n">h</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">P</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">→</span> <span class="kt">Prop</span><span class="o">}</span> <span class="o">{</span><span class="n">x</span> <span class="o">:</span> <span class="n">X</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="bp">∀ᶠ</span> <span class="n">y</span> <span class="k">in</span> <span class="bp">𝓝</span> <span class="n">x</span><span class="o">,</span> <span class="n">P</span> <span class="n">y</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∀ᶠ</span> <span class="n">y</span> <span class="k">in</span> <span class="bp">𝓝</span> <span class="n">x</span><span class="o">,</span> <span class="bp">∀ᶠ</span> <span class="n">z</span> <span class="k">in</span> <span class="bp">𝓝</span> <span class="n">y</span><span class="o">,</span> <span class="n">P</span> <span class="n">z</span> <span class="o">:=</span> <span class="n">eventually_eventually_nhds.mpr</span> <span class="n">h</span> </pre></div> </div> <p>Those two results characterize the functions <code class="docutils literal notranslate"><span class="pre">X</span> <span class="pre">→</span> <span class="pre">Filter</span> <span class="pre">X</span></code> that are neighborhood functions for a topological space
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@@ -950,10 +946,10 @@ structure on <code class="docutils literal notranslate"><span class="pre">X</spabut it will give back its input as a neighborhood function only if it satisfies the above two constraints. More precisely we have a lemma <code class="docutils literal notranslate"><span class="pre">TopologicalSpace.nhds_mkOfNhds</span></code> saying that in a different way and our next exercise deduces this different way from how we stated it above.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Filter</span><span class="w"> </span><span class="n">α</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">H₀</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="n">pure</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">a</span><span class="o">)</span> <span class="w"> </span><span class="o">(</span><span class="n">H</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="o">,</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="kt">Prop</span><span class="o">,</span><span class="w"> </span><span class="o">(</span><span class="bp">∀ᶠ</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="bp">∀ᶠ</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="bp">∀ᶠ</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">y</span><span class="o">,</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a'</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">t</span><span class="o">,</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">a'</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">Filter</span> <span class="n">α</span><span class="o">)</span> <span class="o">(</span><span class="n">H₀</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span><span class="o">,</span> <span class="n">pure</span> <span class="n">a</span> <span class="bp">≤</span> <span class="n">n</span> <span class="n">a</span><span class="o">)</span> <span class="o">(</span><span class="n">H</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span> <span class="o">:</span> <span class="n">α</span><span class="o">,</span> <span class="bp">∀</span> <span class="n">p</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="kt">Prop</span><span class="o">,</span> <span class="o">(</span><span class="bp">∀ᶠ</span> <span class="n">x</span> <span class="k">in</span> <span class="n">n</span> <span class="n">a</span><span class="o">,</span> <span class="n">p</span> <span class="n">x</span><span class="o">)</span> <span class="bp">→</span> <span class="bp">∀ᶠ</span> <span class="n">y</span> <span class="k">in</span> <span class="n">n</span> <span class="n">a</span><span class="o">,</span> <span class="bp">∀ᶠ</span> <span class="n">x</span> <span class="k">in</span> <span class="n">n</span> <span class="n">y</span><span class="o">,</span> <span class="n">p</span> <span class="n">x</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">a</span><span class="o">,</span> <span class="bp">∀</span> <span class="n">s</span> <span class="bp">∈</span> <span class="n">n</span> <span class="n">a</span><span class="o">,</span> <span class="bp">∃</span> <span class="n">t</span> <span class="bp">∈</span> <span class="n">n</span> <span class="n">a</span><span class="o">,</span> <span class="n">t</span> <span class="bp">⊆</span> <span class="n">s</span> <span class="bp">∧</span> <span class="bp">∀</span> <span class="n">a'</span> <span class="bp">∈</span> <span class="n">t</span><span class="o">,</span> <span class="n">s</span> <span class="bp">∈</span> <span class="n">n</span> <span class="n">a'</span> <span class="o">:=</span> <span class="gr">sorry</span> </pre></div> </div> <p>Note that <code class="docutils literal notranslate"><span class="pre">TopologicalSpace.mkOfNhds</span></code> is not so frequently used, but it still good to know in what
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@@ -975,17 +971,17 @@ sequences of functions is a respectable notion of convergence. But there is no da map <code class="docutils literal notranslate"><span class="pre">f</span> <span class="pre">:</span> <span class="pre">X</span> <span class="pre">→</span> <span class="pre">(ℝ</span> <span class="pre">→</span> <span class="pre">ℝ)</span></code> is continuous if and only if <code class="docutils literal notranslate"><span class="pre">fun</span> <span class="pre">x</span> <span class="pre">↦</span> <span class="pre">f</span> <span class="pre">x</span> <span class="pre">t</span></code> is continuous for every <code class="docutils literal notranslate"><span class="pre">t</span> <span class="pre">:</span> <span class="pre">ℝ</span></code>.</p> <p>We now review the data used to solve all those issues. First we can use any map <code class="docutils literal notranslate"><span class="pre">f</span> <span class="pre">:</span> <span class="pre">X</span> <span class="pre">→</span> <span class="pre">Y</span></code> to push or pull topologies from one side to the other. Those two operations form a Galois connection.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">X</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">X</span> <span class="n">Y</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Y</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">TopologicalSpace</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">TopologicalSpace</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">TopologicalSpace.coinduced</span><span class="w"> </span><span class="n">f</span> <span class="kd">example</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">→</span> <span class="n">Y</span><span class="o">)</span> <span class="o">:</span> <span class="n">TopologicalSpace</span> <span class="n">X</span> <span class="bp">→</span> <span class="n">TopologicalSpace</span> <span class="n">Y</span> <span class="o">:=</span> <span class="n">TopologicalSpace.coinduced</span> <span class="n">f</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Y</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">TopologicalSpace</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">TopologicalSpace</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">TopologicalSpace.induced</span><span class="w"> </span><span class="n">f</span> <span class="kd">example</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">→</span> <span class="n">Y</span><span class="o">)</span> <span class="o">:</span> <span class="n">TopologicalSpace</span> <span class="n">Y</span> <span class="bp">→</span> <span class="n">TopologicalSpace</span> <span class="n">X</span> <span class="o">:=</span> <span class="n">TopologicalSpace.induced</span> <span class="n">f</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Y</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">T_X</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">TopologicalSpace</span><span class="w"> </span><span class="n">X</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">T_Y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">TopologicalSpace</span><span class="w"> </span><span class="n">Y</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">TopologicalSpace.coinduced</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">T_X</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">T_Y</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">T_X</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">TopologicalSpace.induced</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">T_Y</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">coinduced_le_iff_le_induced</span> <span class="kd">example</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">→</span> <span class="n">Y</span><span class="o">)</span> <span class="o">(</span><span class="n">T_X</span> <span class="o">:</span> <span class="n">TopologicalSpace</span> <span class="n">X</span><span class="o">)</span> <span class="o">(</span><span class="n">T_Y</span> <span class="o">:</span> <span class="n">TopologicalSpace</span> <span class="n">Y</span><span class="o">)</span> <span class="o">:</span> <span class="n">TopologicalSpace.coinduced</span> <span class="n">f</span> <span class="n">T_X</span> <span class="bp">≤</span> <span class="n">T_Y</span> <span class="bp">↔</span> <span class="n">T_X</span> <span class="bp">≤</span> <span class="n">TopologicalSpace.induced</span> <span class="n">f</span> <span class="n">T_Y</span> <span class="o">:=</span> <span class="n">coinduced_le_iff_le_induced</span> </pre></div> </div> <p>Those operations are compactible with composition of functions.
-
@@ -1001,14 +997,14 @@ on neighborhoods more than open sets so, for any <code class="docutils literal nAnd we know the order relation on <code class="docutils literal notranslate"><span class="pre">Filter</span> <span class="pre">X</span></code> is designed to ensure an order preserving <code class="docutils literal notranslate"><span class="pre">principal</span> <span class="pre">:</span> <span class="pre">Set</span> <span class="pre">X</span> <span class="pre">→</span> <span class="pre">Filter</span> <span class="pre">X</span></code>, allowing to see filters as generalized sets. So the order relation we do use on <code class="docutils literal notranslate"><span class="pre">TopologicalSpace</span> <span class="pre">X</span></code> is opposite to the one coming from <code class="docutils literal notranslate"><span class="pre">Set</span> <span class="pre">(Set</span> <span class="pre">X)</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">T</span><span class="w"> </span><span class="n">T'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">TopologicalSpace</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">T'</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="n">T'.IsOpen</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">T.IsOpen</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Iff.rfl</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">T</span> <span class="n">T'</span> <span class="o">:</span> <span class="n">TopologicalSpace</span> <span class="n">X</span><span class="o">}</span> <span class="o">:</span> <span class="n">T</span> <span class="bp">≤</span> <span class="n">T'</span> <span class="bp">↔</span> <span class="bp">∀</span> <span class="n">s</span><span class="o">,</span> <span class="n">T'.IsOpen</span> <span class="n">s</span> <span class="bp">→</span> <span class="n">T.IsOpen</span> <span class="n">s</span> <span class="o">:=</span> <span class="n">Iff.rfl</span> </pre></div> </div> <p>Now we can recover continuity by combining the push-forward (or pull-back) operation with the order relation.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">T_X</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">TopologicalSpace</span><span class="w"> </span><span class="n">X</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">T_Y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">TopologicalSpace</span><span class="w"> </span><span class="n">Y</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Y</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">Continuous</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">TopologicalSpace.coinduced</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">T_X</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">T_Y</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">continuous_iff_coinduced_le</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">T_X</span> <span class="o">:</span> <span class="n">TopologicalSpace</span> <span class="n">X</span><span class="o">)</span> <span class="o">(</span><span class="n">T_Y</span> <span class="o">:</span> <span class="n">TopologicalSpace</span> <span class="n">Y</span><span class="o">)</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">→</span> <span class="n">Y</span><span class="o">)</span> <span class="o">:</span> <span class="n">Continuous</span> <span class="n">f</span> <span class="bp">↔</span> <span class="n">TopologicalSpace.coinduced</span> <span class="n">f</span> <span class="n">T_X</span> <span class="bp">≤</span> <span class="n">T_Y</span> <span class="o">:=</span> <span class="n">continuous_iff_coinduced_le</span> </pre></div> </div> <p>With this definition and the compatibility of push-forward and composition, we
-
@@ -1019,11 +1015,11 @@ a function <span class="math notranslate nohighlight">\(g : Y → Z\)</span>\[\begin{split}g \text{ continuous } &⇔ g_*(f_*T_X) ≤ T_Z \\ &⇔ (g ∘ f)_* T_X ≤ T_Z \\ &⇔ g ∘ f \text{ continuous}\end{split}\]</div> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">Z</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Y</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">T_X</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">TopologicalSpace</span><span class="w"> </span><span class="n">X</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">T_Z</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">TopologicalSpace</span><span class="w"> </span><span class="n">Z</span><span class="o">)</span> <span class="w"> </span><span class="o">(</span><span class="n">g</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Z</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="bp">@</span><span class="n">Continuous</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="n">Z</span><span class="w"> </span><span class="o">(</span><span class="n">TopologicalSpace.coinduced</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">T_X</span><span class="o">)</span><span class="w"> </span><span class="n">T_Z</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="bp">↔</span> <span class="w"> </span><span class="bp">@</span><span class="n">Continuous</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="n">Z</span><span class="w"> </span><span class="n">T_X</span><span class="w"> </span><span class="n">T_Z</span><span class="w"> </span><span class="o">(</span><span class="n">g</span><span class="w"> </span><span class="bp">∘</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">rw</span><span class="w"> </span><span class="o">[</span><span class="n">continuous_iff_coinduced_le</span><span class="o">,</span><span class="w"> </span><span class="n">coinduced_compose</span><span class="o">,</span><span class="w"> </span><span class="n">continuous_iff_coinduced_le</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">Z</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">→</span> <span class="n">Y</span><span class="o">)</span> <span class="o">(</span><span class="n">T_X</span> <span class="o">:</span> <span class="n">TopologicalSpace</span> <span class="n">X</span><span class="o">)</span> <span class="o">(</span><span class="n">T_Z</span> <span class="o">:</span> <span class="n">TopologicalSpace</span> <span class="n">Z</span><span class="o">)</span> <span class="o">(</span><span class="n">g</span> <span class="o">:</span> <span class="n">Y</span> <span class="bp">→</span> <span class="n">Z</span><span class="o">)</span> <span class="o">:</span> <span class="bp">@</span><span class="n">Continuous</span> <span class="n">Y</span> <span class="n">Z</span> <span class="o">(</span><span class="n">TopologicalSpace.coinduced</span> <span class="n">f</span> <span class="n">T_X</span><span class="o">)</span> <span class="n">T_Z</span> <span class="n">g</span> <span class="bp">↔</span> <span class="bp">@</span><span class="n">Continuous</span> <span class="n">X</span> <span class="n">Z</span> <span class="n">T_X</span> <span class="n">T_Z</span> <span class="o">(</span><span class="n">g</span> <span class="bp">∘</span> <span class="n">f</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">rw</span> <span class="o">[</span><span class="n">continuous_iff_coinduced_le</span><span class="o">,</span> <span class="n">coinduced_compose</span><span class="o">,</span> <span class="n">continuous_iff_coinduced_le</span><span class="o">]</span> </pre></div> </div> <p>So we already get quotient topologies (using the projection map as <code class="docutils literal notranslate"><span class="pre">f</span></code>). This wasn’t using that
-
@@ -1040,17 +1036,17 @@ Let us explore that constraint “on paper” using notation <span class&⇔ ∀ i, f_* T_Z ≤ (p_i)^*T_{X_i}\\ &⇔ f_* T_Z ≤ \inf \left[(p_i)^*T_{X_i}\right]\end{split}\]</div> <p>So we see that what is the topology we want on <code class="docutils literal notranslate"><span class="pre">Π</span> <span class="pre">i,</span> <span class="pre">X</span> <span class="pre">i</span></code>:</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">ι</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">X</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">T_X</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">TopologicalSpace</span><span class="w"> </span><span class="o">(</span><span class="n">X</span><span class="w"> </span><span class="n">i</span><span class="o">))</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="o">(</span><span class="k">Pi</span><span class="bp">.</span><span class="n">topologicalSpace</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">TopologicalSpace</span><span class="w"> </span><span class="o">(</span><span class="bp">∀</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="n">i</span><span class="o">))</span><span class="w"> </span><span class="bp">=</span> <span class="w"> </span><span class="bp">⨅</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">TopologicalSpace.induced</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">T_X</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">ι</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">)</span> <span class="o">(</span><span class="n">X</span> <span class="o">:</span> <span class="n">ι</span> <span class="bp">→</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">)</span> <span class="o">(</span><span class="n">T_X</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">i</span><span class="o">,</span> <span class="n">TopologicalSpace</span> <span class="o">(</span><span class="n">X</span> <span class="n">i</span><span class="o">))</span> <span class="o">:</span> <span class="o">(</span><span class="k">Pi</span><span class="bp">.</span><span class="n">topologicalSpace</span> <span class="o">:</span> <span class="n">TopologicalSpace</span> <span class="o">(</span><span class="bp">∀</span> <span class="n">i</span><span class="o">,</span> <span class="n">X</span> <span class="n">i</span><span class="o">))</span> <span class="bp">=</span> <span class="bp">⨅</span> <span class="n">i</span><span class="o">,</span> <span class="n">TopologicalSpace.induced</span> <span class="o">(</span><span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">x</span> <span class="n">i</span><span class="o">)</span> <span class="o">(</span><span class="n">T_X</span> <span class="n">i</span><span class="o">)</span> <span class="o">:=</span> <span class="n">rfl</span> </pre></div> </div> <p>This ends our tour of how Mathlib thinks that topological spaces fix defects of the theory of metric spaces by being a more functorial theory and having a complete lattice structure for any fixed type.</p> </section> <section id="separation-and-countability"> <h3><span class="section-number">10.3.2. </span>Separation and countability<a class="headerlink" href="#separation-and-countability" title="Link to this heading"></a></h3> <h3><span class="section-number">10.3.2. </span>Separation and countability<a class="headerlink" href="#separation-and-countability" title="Permalink to this heading"></a></h3> <p>We saw that the category of topological spaces have very nice properties. The price to pay for this is existence of rather pathological topological spaces. There are a number of assumptions you can make on a topological space to ensure its behavior
-
@@ -1058,19 +1054,19 @@ is closer to what metric spaces do. The most important is <code class="docutilsthat will ensure that limits are unique. A stronger separation property is <code class="docutils literal notranslate"><span class="pre">T3Space</span></code> that ensures in addition the <cite>RegularSpace</cite> property: each point has a basis of closed neighborhoods.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">[</span><span class="n">TopologicalSpace</span><span class="w"> </span><span class="n">X</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">T2Space</span><span class="w"> </span><span class="n">X</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">u</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">ha</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Tendsto</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="n">atTop</span><span class="w"> </span><span class="o">(</span><span class="n">𝓝</span><span class="w"> </span><span class="n">a</span><span class="o">))</span> <span class="w"> </span><span class="o">(</span><span class="n">hb</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Tendsto</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="n">atTop</span><span class="w"> </span><span class="o">(</span><span class="n">𝓝</span><span class="w"> </span><span class="n">b</span><span class="o">))</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">tendsto_nhds_unique</span><span class="w"> </span><span class="n">ha</span><span class="w"> </span><span class="n">hb</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">[</span><span class="n">TopologicalSpace</span> <span class="n">X</span><span class="o">]</span> <span class="o">[</span><span class="n">T2Space</span> <span class="n">X</span><span class="o">]</span> <span class="o">{</span><span class="n">u</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">X</span><span class="o">}</span> <span class="o">{</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">X</span><span class="o">}</span> <span class="o">(</span><span class="n">ha</span> <span class="o">:</span> <span class="n">Tendsto</span> <span class="n">u</span> <span class="n">atTop</span> <span class="o">(</span><span class="bp">𝓝</span> <span class="n">a</span><span class="o">))</span> <span class="o">(</span><span class="n">hb</span> <span class="o">:</span> <span class="n">Tendsto</span> <span class="n">u</span> <span class="n">atTop</span> <span class="o">(</span><span class="bp">𝓝</span> <span class="n">b</span><span class="o">))</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">=</span> <span class="n">b</span> <span class="o">:=</span> <span class="n">tendsto_nhds_unique</span> <span class="n">ha</span> <span class="n">hb</span> <span class="kd">example</span><span class="w"> </span><span class="o">[</span><span class="n">TopologicalSpace</span><span class="w"> </span><span class="n">X</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">RegularSpace</span><span class="w"> </span><span class="n">X</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="o">(</span><span class="n">𝓝</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="bp">.</span><span class="n">HasBasis</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">𝓝</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">IsClosed</span><span class="w"> </span><span class="n">s</span><span class="o">)</span><span class="w"> </span><span class="n">id</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">closed_nhds_basis</span><span class="w"> </span><span class="n">a</span> <span class="kd">example</span> <span class="o">[</span><span class="n">TopologicalSpace</span> <span class="n">X</span><span class="o">]</span> <span class="o">[</span><span class="n">RegularSpace</span> <span class="n">X</span><span class="o">]</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">X</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="bp">𝓝</span> <span class="n">a</span><span class="o">)</span><span class="bp">.</span><span class="n">HasBasis</span> <span class="o">(</span><span class="k">fun</span> <span class="n">s</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">X</span> <span class="bp">↦</span> <span class="n">s</span> <span class="bp">∈</span> <span class="bp">𝓝</span> <span class="n">a</span> <span class="bp">∧</span> <span class="n">IsClosed</span> <span class="n">s</span><span class="o">)</span> <span class="n">id</span> <span class="o">:=</span> <span class="n">closed_nhds_basis</span> <span class="n">a</span> </pre></div> </div> <p>Note that, in every topological space, each point has a basis of open neighborhood, by definition.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">[</span><span class="n">TopologicalSpace</span><span class="w"> </span><span class="n">X</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="o">(</span><span class="n">𝓝</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="bp">.</span><span class="n">HasBasis</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">𝓝</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">IsOpen</span><span class="w"> </span><span class="n">t</span><span class="o">)</span><span class="w"> </span><span class="n">id</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">nhds_basis_opens'</span><span class="w"> </span><span class="n">x</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">[</span><span class="n">TopologicalSpace</span> <span class="n">X</span><span class="o">]</span> <span class="o">{</span><span class="n">x</span> <span class="o">:</span> <span class="n">X</span><span class="o">}</span> <span class="o">:</span> <span class="o">(</span><span class="bp">𝓝</span> <span class="n">x</span><span class="o">)</span><span class="bp">.</span><span class="n">HasBasis</span> <span class="o">(</span><span class="k">fun</span> <span class="n">t</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">X</span> <span class="bp">↦</span> <span class="n">t</span> <span class="bp">∈</span> <span class="bp">𝓝</span> <span class="n">x</span> <span class="bp">∧</span> <span class="n">IsOpen</span> <span class="n">t</span><span class="o">)</span> <span class="n">id</span> <span class="o">:=</span> <span class="n">nhds_basis_opens'</span> <span class="n">x</span> </pre></div> </div> <p>Our main goal is now to prove the basic theorem which allows extension by continuity.
-
@@ -1088,11 +1084,11 @@ The assumption “tends to <span class="math notranslate nohighlight">\(x\)<<code class="docutils literal notranslate"><span class="pre">comap</span> <span class="pre">(↑)</span> <span class="pre">(𝓝</span> <span class="pre">x)</span></code>.</p> <p>Let’s first prove an auxiliary lemma, extracted to simplify the context (in particular we don’t need Y to be a topological space here).</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span><span class="w"> </span><span class="n">aux</span><span class="w"> </span><span class="o">{</span><span class="n">X</span><span class="w"> </span><span class="n">Y</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">TopologicalSpace</span><span class="w"> </span><span class="n">X</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">X</span><span class="o">}</span> <span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Y</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">F</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Filter</span><span class="w"> </span><span class="n">Y</span><span class="o">}</span> <span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Tendsto</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">comap</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">(</span><span class="n">𝓝</span><span class="w"> </span><span class="n">x</span><span class="o">))</span><span class="w"> </span><span class="n">F</span><span class="o">)</span><span class="w"> </span><span class="o">{</span><span class="n">V'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">Y</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">V'_in</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">V'</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">F</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">𝓝</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">IsOpen</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">⁻¹'</span><span class="w"> </span><span class="n">V</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">⁻¹'</span><span class="w"> </span><span class="n">V'</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">theorem</span> <span class="n">aux</span> <span class="o">{</span><span class="n">X</span> <span class="n">Y</span> <span class="n">A</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">TopologicalSpace</span> <span class="n">X</span><span class="o">]</span> <span class="o">{</span><span class="n">c</span> <span class="o">:</span> <span class="n">A</span> <span class="bp">→</span> <span class="n">X</span><span class="o">}</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">A</span> <span class="bp">→</span> <span class="n">Y</span><span class="o">}</span> <span class="o">{</span><span class="n">x</span> <span class="o">:</span> <span class="n">X</span><span class="o">}</span> <span class="o">{</span><span class="n">F</span> <span class="o">:</span> <span class="n">Filter</span> <span class="n">Y</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">Tendsto</span> <span class="n">f</span> <span class="o">(</span><span class="n">comap</span> <span class="n">c</span> <span class="o">(</span><span class="bp">𝓝</span> <span class="n">x</span><span class="o">))</span> <span class="n">F</span><span class="o">)</span> <span class="o">{</span><span class="n">V'</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">Y</span><span class="o">}</span> <span class="o">(</span><span class="n">V'_in</span> <span class="o">:</span> <span class="n">V'</span> <span class="bp">∈</span> <span class="n">F</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">V</span> <span class="bp">∈</span> <span class="bp">𝓝</span> <span class="n">x</span><span class="o">,</span> <span class="n">IsOpen</span> <span class="n">V</span> <span class="bp">∧</span> <span class="n">c</span> <span class="bp">⁻¹'</span> <span class="n">V</span> <span class="bp">⊆</span> <span class="n">f</span> <span class="bp">⁻¹'</span> <span class="n">V'</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> </pre></div> </div> <p>Let’s now turn to the main proof of the extension by continuity theorem.</p>
-
@@ -1118,28 +1114,28 @@ Because we know <code class="docutils literal notranslate"><span class="pre">Ten<code class="docutils literal notranslate"><span class="pre">φ</span> <span class="pre">y</span> <span class="pre">∈</span> <span class="pre">closure</span> <span class="pre">V'</span></code> and, since <code class="docutils literal notranslate"><span class="pre">V'</span></code> is closed, we have proved <code class="docutils literal notranslate"><span class="pre">φ</span> <span class="pre">y</span> <span class="pre">∈</span> <span class="pre">V'</span></code>.</p> <p>It remains to prove that <code class="docutils literal notranslate"><span class="pre">φ</span></code> extends <code class="docutils literal notranslate"><span class="pre">f</span></code>. This is where the continuity of <code class="docutils literal notranslate"><span class="pre">f</span></code> enters the discussion, together with the fact that <code class="docutils literal notranslate"><span class="pre">Y</span></code> is Hausdorff.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">[</span><span class="n">TopologicalSpace</span><span class="w"> </span><span class="n">X</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">TopologicalSpace</span><span class="w"> </span><span class="n">Y</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">T3Space</span><span class="w"> </span><span class="n">Y</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">A</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">X</span><span class="o">}</span> <span class="w"> </span><span class="o">(</span><span class="n">hA</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">closure</span><span class="w"> </span><span class="n">A</span><span class="o">)</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Y</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">f_cont</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Continuous</span><span class="w"> </span><span class="n">f</span><span class="o">)</span> <span class="w"> </span><span class="o">(</span><span class="n">hf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="o">,</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Y</span><span class="o">,</span><span class="w"> </span><span class="n">Tendsto</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">comap</span><span class="w"> </span><span class="o">(</span><span class="bp">↑</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">𝓝</span><span class="w"> </span><span class="n">x</span><span class="o">))</span><span class="w"> </span><span class="o">(</span><span class="n">𝓝</span><span class="w"> </span><span class="n">c</span><span class="o">))</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Y</span><span class="o">,</span><span class="w"> </span><span class="n">Continuous</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">A</span><span class="o">,</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">[</span><span class="n">TopologicalSpace</span> <span class="n">X</span><span class="o">]</span> <span class="o">[</span><span class="n">TopologicalSpace</span> <span class="n">Y</span><span class="o">]</span> <span class="o">[</span><span class="n">T3Space</span> <span class="n">Y</span><span class="o">]</span> <span class="o">{</span><span class="n">A</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">X</span><span class="o">}</span> <span class="o">(</span><span class="n">hA</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span><span class="o">,</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">closure</span> <span class="n">A</span><span class="o">)</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">A</span> <span class="bp">→</span> <span class="n">Y</span><span class="o">}</span> <span class="o">(</span><span class="n">f_cont</span> <span class="o">:</span> <span class="n">Continuous</span> <span class="n">f</span><span class="o">)</span> <span class="o">(</span><span class="n">hf</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span> <span class="o">:</span> <span class="n">X</span><span class="o">,</span> <span class="bp">∃</span> <span class="n">c</span> <span class="o">:</span> <span class="n">Y</span><span class="o">,</span> <span class="n">Tendsto</span> <span class="n">f</span> <span class="o">(</span><span class="n">comap</span> <span class="o">(</span><span class="bp">↑</span><span class="o">)</span> <span class="o">(</span><span class="bp">𝓝</span> <span class="n">x</span><span class="o">))</span> <span class="o">(</span><span class="bp">𝓝</span> <span class="n">c</span><span class="o">))</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">φ</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">→</span> <span class="n">Y</span><span class="o">,</span> <span class="n">Continuous</span> <span class="n">φ</span> <span class="bp">∧</span> <span class="bp">∀</span> <span class="n">a</span> <span class="o">:</span> <span class="n">A</span><span class="o">,</span> <span class="n">φ</span> <span class="n">a</span> <span class="bp">=</span> <span class="n">f</span> <span class="n">a</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="k">#check</span><span class="w"> </span><span class="n">HasBasis.tendsto_right_iff</span> <span class="k">#check</span> <span class="n">HasBasis.tendsto_right_iff</span> </pre></div> </div> <p>In addition to separation property, the main kind of assumption you can make on a topological space to bring it closer to metric spaces is countability assumption. The main one is first countability asking that every point has a countable neighborhood basis. In particular this ensures that closure of sets can be understood using sequences.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">[</span><span class="n">TopologicalSpace</span><span class="w"> </span><span class="n">X</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">FirstCountableTopology</span><span class="w"> </span><span class="n">X</span><span class="o">]</span> <span class="w"> </span><span class="o">{</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">closure</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">X</span><span class="o">,</span><span class="w"> </span><span class="o">(</span><span class="bp">∀</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="o">)</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">Tendsto</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="n">atTop</span><span class="w"> </span><span class="o">(</span><span class="n">𝓝</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">mem_closure_iff_seq_limit</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">[</span><span class="n">TopologicalSpace</span> <span class="n">X</span><span class="o">]</span> <span class="o">[</span><span class="n">FirstCountableTopology</span> <span class="n">X</span><span class="o">]</span> <span class="o">{</span><span class="n">s</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">X</span><span class="o">}</span> <span class="o">{</span><span class="n">a</span> <span class="o">:</span> <span class="n">X</span><span class="o">}</span> <span class="o">:</span> <span class="n">a</span> <span class="bp">∈</span> <span class="n">closure</span> <span class="n">s</span> <span class="bp">↔</span> <span class="bp">∃</span> <span class="n">u</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">X</span><span class="o">,</span> <span class="o">(</span><span class="bp">∀</span> <span class="n">n</span><span class="o">,</span> <span class="n">u</span> <span class="n">n</span> <span class="bp">∈</span> <span class="n">s</span><span class="o">)</span> <span class="bp">∧</span> <span class="n">Tendsto</span> <span class="n">u</span> <span class="n">atTop</span> <span class="o">(</span><span class="bp">𝓝</span> <span class="n">a</span><span class="o">)</span> <span class="o">:=</span> <span class="n">mem_closure_iff_seq_limit</span> </pre></div> </div> </section> <section id="id5"> <h3><span class="section-number">10.3.3. </span>Compactness<a class="headerlink" href="#id5" title="Link to this heading"></a></h3> <h3><span class="section-number">10.3.3. </span>Compactness<a class="headerlink" href="#id5" title="Permalink to this heading"></a></h3> <p>Let us now discuss how compactness is defined for topological spaces. As usual there are several ways to think about it and Mathlib goes for the filter version.</p> <p>We first need to define cluster points of filters. Given a filter <code class="docutils literal notranslate"><span class="pre">F</span></code> on a topological space <code class="docutils literal notranslate"><span class="pre">X</span></code>,
-
@@ -1147,14 +1143,14 @@ a point <code class="docutils literal notranslate"><span class="pre">x</span> <swith the generalized set of points that are close to <code class="docutils literal notranslate"><span class="pre">x</span></code>.</p> <p>Then we can say that a set <code class="docutils literal notranslate"><span class="pre">s</span></code> is compact if every nonempty generalized set <code class="docutils literal notranslate"><span class="pre">F</span></code> contained in <code class="docutils literal notranslate"><span class="pre">s</span></code>, i.e. such that <code class="docutils literal notranslate"><span class="pre">F</span> <span class="pre">≤</span> <span class="pre">𝓟</span> <span class="pre">s</span></code>, has a cluster point in <code class="docutils literal notranslate"><span class="pre">s</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">[</span><span class="n">TopologicalSpace</span><span class="w"> </span><span class="n">X</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">[</span><span class="n">TopologicalSpace</span> <span class="n">X</span><span class="o">]</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">F</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Filter</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ClusterPt</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">NeBot</span><span class="w"> </span><span class="o">(</span><span class="n">𝓝</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">F</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Iff.rfl</span> <span class="kd">example</span> <span class="o">{</span><span class="n">F</span> <span class="o">:</span> <span class="n">Filter</span> <span class="n">X</span><span class="o">}</span> <span class="o">{</span><span class="n">x</span> <span class="o">:</span> <span class="n">X</span><span class="o">}</span> <span class="o">:</span> <span class="n">ClusterPt</span> <span class="n">x</span> <span class="n">F</span> <span class="bp">↔</span> <span class="n">NeBot</span> <span class="o">(</span><span class="bp">𝓝</span> <span class="n">x</span> <span class="bp">⊓</span> <span class="n">F</span><span class="o">)</span> <span class="o">:=</span> <span class="n">Iff.rfl</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">IsCompact</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="o">(</span><span class="n">F</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Filter</span><span class="w"> </span><span class="n">X</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">NeBot</span><span class="w"> </span><span class="n">F</span><span class="o">],</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">𝓟</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="n">ClusterPt</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Iff.rfl</span> <span class="kd">example</span> <span class="o">{</span><span class="n">s</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">X</span><span class="o">}</span> <span class="o">:</span> <span class="n">IsCompact</span> <span class="n">s</span> <span class="bp">↔</span> <span class="bp">∀</span> <span class="o">(</span><span class="n">F</span> <span class="o">:</span> <span class="n">Filter</span> <span class="n">X</span><span class="o">)</span> <span class="o">[</span><span class="n">NeBot</span> <span class="n">F</span><span class="o">],</span> <span class="n">F</span> <span class="bp">≤</span> <span class="bp">𝓟</span> <span class="n">s</span> <span class="bp">→</span> <span class="bp">∃</span> <span class="n">a</span> <span class="bp">∈</span> <span class="n">s</span><span class="o">,</span> <span class="n">ClusterPt</span> <span class="n">a</span> <span class="n">F</span> <span class="o">:=</span> <span class="n">Iff.rfl</span> </pre></div> </div> <p>For instance if <code class="docutils literal notranslate"><span class="pre">F</span></code> is <code class="docutils literal notranslate"><span class="pre">map</span> <span class="pre">u</span> <span class="pre">atTop</span></code>, the image under <code class="docutils literal notranslate"><span class="pre">u</span> <span class="pre">:</span> <span class="pre">ℕ</span> <span class="pre">→</span> <span class="pre">X</span></code> of <code class="docutils literal notranslate"><span class="pre">atTop</span></code>, the generalized set
-
@@ -1163,36 +1159,36 @@ large enough. Saying that <code class="docutils literal notranslate"><span classintersects the set of points that are close to <code class="docutils literal notranslate"><span class="pre">x</span></code>. In case <code class="docutils literal notranslate"><span class="pre">𝓝</span> <span class="pre">x</span></code> has a countable basis, we can interpret this as saying that <code class="docutils literal notranslate"><span class="pre">u</span></code> has a subsequence converging to <code class="docutils literal notranslate"><span class="pre">x</span></code>, and we get back what compactness looks like in metric spaces.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">[</span><span class="n">FirstCountableTopology</span><span class="w"> </span><span class="n">X</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">u</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hs</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">IsCompact</span><span class="w"> </span><span class="n">s</span><span class="o">)</span> <span class="w"> </span><span class="o">(</span><span class="n">hu</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℕ</span><span class="o">,</span><span class="w"> </span><span class="n">StrictMono</span><span class="w"> </span><span class="n">φ</span><span class="w"> </span><span class="bp">∧</span><span class="w"> </span><span class="n">Tendsto</span><span class="w"> </span><span class="o">(</span><span class="n">u</span><span class="w"> </span><span class="bp">∘</span><span class="w"> </span><span class="n">φ</span><span class="o">)</span><span class="w"> </span><span class="n">atTop</span><span class="w"> </span><span class="o">(</span><span class="n">𝓝</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">hs.tendsto_subseq</span><span class="w"> </span><span class="n">hu</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">[</span><span class="n">FirstCountableTopology</span> <span class="n">X</span><span class="o">]</span> <span class="o">{</span><span class="n">s</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">X</span><span class="o">}</span> <span class="o">{</span><span class="n">u</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">X</span><span class="o">}</span> <span class="o">(</span><span class="n">hs</span> <span class="o">:</span> <span class="n">IsCompact</span> <span class="n">s</span><span class="o">)</span> <span class="o">(</span><span class="n">hu</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">n</span><span class="o">,</span> <span class="n">u</span> <span class="n">n</span> <span class="bp">∈</span> <span class="n">s</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">a</span> <span class="bp">∈</span> <span class="n">s</span><span class="o">,</span> <span class="bp">∃</span> <span class="n">φ</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">ℕ</span><span class="o">,</span> <span class="n">StrictMono</span> <span class="n">φ</span> <span class="bp">∧</span> <span class="n">Tendsto</span> <span class="o">(</span><span class="n">u</span> <span class="bp">∘</span> <span class="n">φ</span><span class="o">)</span> <span class="n">atTop</span> <span class="o">(</span><span class="bp">𝓝</span> <span class="n">a</span><span class="o">)</span> <span class="o">:=</span> <span class="n">hs.tendsto_subseq</span> <span class="n">hu</span> </pre></div> </div> <p>Cluster points behave nicely with continuous functions.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">[</span><span class="n">TopologicalSpace</span><span class="w"> </span><span class="n">Y</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">[</span><span class="n">TopologicalSpace</span> <span class="n">Y</span><span class="o">]</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">F</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Filter</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Filter</span><span class="w"> </span><span class="n">Y</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">H</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ClusterPt</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">F</span><span class="o">)</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Y</span><span class="o">}</span> <span class="w"> </span><span class="o">(</span><span class="n">hfx</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ContinuousAt</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Tendsto</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ClusterPt</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">ClusterPt.map</span><span class="w"> </span><span class="n">H</span><span class="w"> </span><span class="n">hfx</span><span class="w"> </span><span class="n">hf</span> <span class="kd">example</span> <span class="o">{</span><span class="n">x</span> <span class="o">:</span> <span class="n">X</span><span class="o">}</span> <span class="o">{</span><span class="n">F</span> <span class="o">:</span> <span class="n">Filter</span> <span class="n">X</span><span class="o">}</span> <span class="o">{</span><span class="n">G</span> <span class="o">:</span> <span class="n">Filter</span> <span class="n">Y</span><span class="o">}</span> <span class="o">(</span><span class="n">H</span> <span class="o">:</span> <span class="n">ClusterPt</span> <span class="n">x</span> <span class="n">F</span><span class="o">)</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">→</span> <span class="n">Y</span><span class="o">}</span> <span class="o">(</span><span class="n">hfx</span> <span class="o">:</span> <span class="n">ContinuousAt</span> <span class="n">f</span> <span class="n">x</span><span class="o">)</span> <span class="o">(</span><span class="n">hf</span> <span class="o">:</span> <span class="n">Tendsto</span> <span class="n">f</span> <span class="n">F</span> <span class="n">G</span><span class="o">)</span> <span class="o">:</span> <span class="n">ClusterPt</span> <span class="o">(</span><span class="n">f</span> <span class="n">x</span><span class="o">)</span> <span class="n">G</span> <span class="o">:=</span> <span class="n">ClusterPt.map</span> <span class="n">H</span> <span class="n">hfx</span> <span class="n">hf</span> </pre></div> </div> <p>As an exercise, we will prove that the image of a compact set under a continuous map is compact. In addition to what we saw already, you should use <code class="docutils literal notranslate"><span class="pre">Filter.push_pull</span></code> and <code class="docutils literal notranslate"><span class="pre">NeBot.of_map</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">[</span><span class="n">TopologicalSpace</span><span class="w"> </span><span class="n">Y</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Y</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Continuous</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">{</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hs</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">IsCompact</span><span class="w"> </span><span class="n">s</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">IsCompact</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="n">s</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="n">intro</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="n">F_ne</span><span class="w"> </span><span class="n">F_le</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">map_eq</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">map</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">𝓟</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">comap</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">F</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">𝓟</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="n">s</span><span class="o">)</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">Hne</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="n">𝓟</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">comap</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">F</span><span class="o">)</span><span class="bp">.</span><span class="n">NeBot</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">Hle</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">𝓟</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">⊓</span><span class="w"> </span><span class="n">comap</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">𝓟</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="n">inf_le_left</span> <span class="w"> </span><span class="gr">sorry</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">[</span><span class="n">TopologicalSpace</span> <span class="n">Y</span><span class="o">]</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">→</span> <span class="n">Y</span><span class="o">}</span> <span class="o">(</span><span class="n">hf</span> <span class="o">:</span> <span class="n">Continuous</span> <span class="n">f</span><span class="o">)</span> <span class="o">{</span><span class="n">s</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">X</span><span class="o">}</span> <span class="o">(</span><span class="n">hs</span> <span class="o">:</span> <span class="n">IsCompact</span> <span class="n">s</span><span class="o">)</span> <span class="o">:</span> <span class="n">IsCompact</span> <span class="o">(</span><span class="n">f</span> <span class="bp">''</span> <span class="n">s</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">intro</span> <span class="n">F</span> <span class="n">F_ne</span> <span class="n">F_le</span> <span class="k">have</span> <span class="n">map_eq</span> <span class="o">:</span> <span class="n">map</span> <span class="n">f</span> <span class="o">(</span><span class="bp">𝓟</span> <span class="n">s</span> <span class="bp">⊓</span> <span class="n">comap</span> <span class="n">f</span> <span class="n">F</span><span class="o">)</span> <span class="bp">=</span> <span class="bp">𝓟</span> <span class="o">(</span><span class="n">f</span> <span class="bp">''</span> <span class="n">s</span><span class="o">)</span> <span class="bp">⊓</span> <span class="n">F</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="k">have</span> <span class="n">Hne</span> <span class="o">:</span> <span class="o">(</span><span class="bp">𝓟</span> <span class="n">s</span> <span class="bp">⊓</span> <span class="n">comap</span> <span class="n">f</span> <span class="n">F</span><span class="o">)</span><span class="bp">.</span><span class="n">NeBot</span> <span class="o">:=</span> <span class="kd">by</span> <span class="gr">sorry</span> <span class="k">have</span> <span class="n">Hle</span> <span class="o">:</span> <span class="bp">𝓟</span> <span class="n">s</span> <span class="bp">⊓</span> <span class="n">comap</span> <span class="n">f</span> <span class="n">F</span> <span class="bp">≤</span> <span class="bp">𝓟</span> <span class="n">s</span> <span class="o">:=</span> <span class="n">inf_le_left</span> <span class="gr">sorry</span> </pre></div> </div> <p>One can also express compactness in terms of open covers: <code class="docutils literal notranslate"><span class="pre">s</span></code> is compact if every family of open sets that cover <code class="docutils literal notranslate"><span class="pre">s</span></code> has a finite covering sub-family.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">ι</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">X</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hs</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">IsCompact</span><span class="w"> </span><span class="n">s</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">U</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">X</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hUo</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">IsOpen</span><span class="w"> </span><span class="o">(</span><span class="n">U</span><span class="w"> </span><span class="n">i</span><span class="o">))</span> <span class="w"> </span><span class="o">(</span><span class="n">hsU</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="bp">⋃</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">U</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Finset</span><span class="w"> </span><span class="n">ι</span><span class="o">,</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="bp">⋃</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">t</span><span class="o">,</span><span class="w"> </span><span class="n">U</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">hs.elim_finite_subcover</span><span class="w"> </span><span class="n">U</span><span class="w"> </span><span class="n">hUo</span><span class="w"> </span><span class="n">hsU</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">ι</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">{</span><span class="n">s</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">X</span><span class="o">}</span> <span class="o">(</span><span class="n">hs</span> <span class="o">:</span> <span class="n">IsCompact</span> <span class="n">s</span><span class="o">)</span> <span class="o">(</span><span class="n">U</span> <span class="o">:</span> <span class="n">ι</span> <span class="bp">→</span> <span class="n">Set</span> <span class="n">X</span><span class="o">)</span> <span class="o">(</span><span class="n">hUo</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">i</span><span class="o">,</span> <span class="n">IsOpen</span> <span class="o">(</span><span class="n">U</span> <span class="n">i</span><span class="o">))</span> <span class="o">(</span><span class="n">hsU</span> <span class="o">:</span> <span class="n">s</span> <span class="bp">⊆</span> <span class="bp">⋃</span> <span class="n">i</span><span class="o">,</span> <span class="n">U</span> <span class="n">i</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">t</span> <span class="o">:</span> <span class="n">Finset</span> <span class="n">ι</span><span class="o">,</span> <span class="n">s</span> <span class="bp">⊆</span> <span class="bp">⋃</span> <span class="n">i</span> <span class="bp">∈</span> <span class="n">t</span><span class="o">,</span> <span class="n">U</span> <span class="n">i</span> <span class="o">:=</span> <span class="n">hs.elim_finite_subcover</span> <span class="n">U</span> <span class="n">hUo</span> <span class="n">hsU</span> </pre></div> </div> </section>
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@@ -97,8 +93,8 @@<div role="main" class="document" itemscope="itemscope" itemtype="http://schema.org/Article"> <div itemprop="articleBody"> <section id="index-0"> <span id="differential-calculus"></span><span id="id1"></span><h1><span class="section-number">11. </span>Differential Calculus<a class="headerlink" href="#index-0" title="Link to this heading"></a></h1> <span class="target" id="differential-calculus"></span><section id="index-0"> <span id="id1"></span><h1><span class="section-number">11. </span>Differential Calculus<a class="headerlink" href="#index-0" title="Permalink to this heading"></a></h1> <p>We now consider the formalization of notions from <em>analysis</em>, starting with differentiation in this chapter and turning integration and measure theory in the next.
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@@ -108,15 +104,15 @@ which is familiar from any introductory calculus class.In <a class="reference internal" href="#normed-spaces"><span class="std std-numref">Section 11.2</span></a>, we then consider the notion of a derivative in a much broader setting.</p> <section id="elementary-differential-calculus"> <span id="index-1"></span><span id="id2"></span><h2><span class="section-number">11.1. </span>Elementary Differential Calculus<a class="headerlink" href="#elementary-differential-calculus" title="Link to this heading"></a></h2> <span id="index-1"></span><span id="id2"></span><h2><span class="section-number">11.1. </span>Elementary Differential Calculus<a class="headerlink" href="#elementary-differential-calculus" title="Permalink to this heading"></a></h2> <p>Let <code class="docutils literal notranslate"><span class="pre">f</span></code> be a function from the reals to the reals. There is a difference between talking about the derivative of <code class="docutils literal notranslate"><span class="pre">f</span></code> at a single point and talking about the derivative function. In Mathlib, the first notion is represented as follows.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span><span class="w"> </span><span class="n">Real</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span> <span class="n">Real</span> <span class="sd">/-- The sin function has derivative 1 at 0. -/</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">HasDerivAt</span><span class="w"> </span><span class="n">sin</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">simpa</span><span class="w"> </span><span class="n">using</span><span class="w"> </span><span class="n">hasDerivAt_sin</span><span class="w"> </span><span class="mi">0</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">HasDerivAt</span> <span class="n">sin</span> <span class="mi">1</span> <span class="mi">0</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simpa</span> <span class="n">using</span> <span class="n">hasDerivAt_sin</span> <span class="mi">0</span> </pre></div> </div> <p>We can also express that <code class="docutils literal notranslate"><span class="pre">f</span></code> is differentiable at a point without
-
@@ -126,8 +122,8 @@ We specify <code class="docutils literal notranslate"><span class="pre">ℝ<when talking about functions from <code class="docutils literal notranslate"><span class="pre">ℂ</span></code> to <code class="docutils literal notranslate"><span class="pre">ℂ</span></code>, we want to be able to distinguish between being differentiable in the real sense and being differentiable in the sense of the complex derivative.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">DifferentiableAt</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="n">sin</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">(</span><span class="n">hasDerivAt_sin</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="bp">.</span><span class="n">differentiableAt</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="n">DifferentiableAt</span> <span class="n">ℝ</span> <span class="n">sin</span> <span class="n">x</span> <span class="o">:=</span> <span class="o">(</span><span class="n">hasDerivAt_sin</span> <span class="n">x</span><span class="o">)</span><span class="bp">.</span><span class="n">differentiableAt</span> </pre></div> </div> <p>It would be inconvenient to have to provide a proof of differentiability
-
@@ -135,19 +131,19 @@ every time we want to refer to a derivative.So Mathlib provides a function <code class="docutils literal notranslate"><span class="pre">deriv</span> <span class="pre">f</span> <span class="pre">:</span> <span class="pre">ℝ</span> <span class="pre">→</span> <span class="pre">ℝ</span></code> that is defined for any function <code class="docutils literal notranslate"><span class="pre">f</span> <span class="pre">:</span> <span class="pre">ℝ</span> <span class="pre">→</span> <span class="pre">ℝ</span></code> but is defined to take the value <code class="docutils literal notranslate"><span class="pre">0</span></code> at any point where <code class="docutils literal notranslate"><span class="pre">f</span></code> is not differentiable.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">HasDerivAt</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">deriv</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">h.deriv</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">{</span><span class="n">x</span> <span class="n">a</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">HasDerivAt</span> <span class="n">f</span> <span class="n">a</span> <span class="n">x</span><span class="o">)</span> <span class="o">:</span> <span class="n">deriv</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">=</span> <span class="n">a</span> <span class="o">:=</span> <span class="n">h.deriv</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">¬</span><span class="n">DifferentiableAt</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">deriv</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">deriv_zero_of_not_differentiableAt</span><span class="w"> </span><span class="n">h</span> <span class="kd">example</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">{</span><span class="n">x</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="bp">¬</span><span class="n">DifferentiableAt</span> <span class="n">ℝ</span> <span class="n">f</span> <span class="n">x</span><span class="o">)</span> <span class="o">:</span> <span class="n">deriv</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">=</span> <span class="mi">0</span> <span class="o">:=</span> <span class="n">deriv_zero_of_not_differentiableAt</span> <span class="n">h</span> </pre></div> </div> <p>Of course there are many lemmas about <code class="docutils literal notranslate"><span class="pre">deriv</span></code> that do require differentiability assumptions. For instance, you should think about a counterexample to the next lemma without the differentiability assumptions.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">DifferentiableAt</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hg</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">DifferentiableAt</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">deriv</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">g</span><span class="o">)</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">deriv</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">deriv</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">deriv_add</span><span class="w"> </span><span class="n">hf</span><span class="w"> </span><span class="n">hg</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">f</span> <span class="n">g</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">{</span><span class="n">x</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">hf</span> <span class="o">:</span> <span class="n">DifferentiableAt</span> <span class="n">ℝ</span> <span class="n">f</span> <span class="n">x</span><span class="o">)</span> <span class="o">(</span><span class="n">hg</span> <span class="o">:</span> <span class="n">DifferentiableAt</span> <span class="n">ℝ</span> <span class="n">g</span> <span class="n">x</span><span class="o">)</span> <span class="o">:</span> <span class="n">deriv</span> <span class="o">(</span><span class="n">f</span> <span class="bp">+</span> <span class="n">g</span><span class="o">)</span> <span class="n">x</span> <span class="bp">=</span> <span class="n">deriv</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">deriv</span> <span class="n">g</span> <span class="n">x</span> <span class="o">:=</span> <span class="n">deriv_add</span> <span class="n">hf</span> <span class="n">hg</span> </pre></div> </div> <p>Interestingly, however, there are statements that can avoid differentiability
-
@@ -156,76 +152,76 @@ of the fact that the value of <code class="docutils literal notranslate"><span cnot differentiable. So making sense of the following statement requires knowing the precise definition of <code class="docutils literal notranslate"><span class="pre">deriv</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">IsLocalMin</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">deriv</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">h.deriv_eq_zero</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">{</span><span class="n">a</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="n">IsLocalMin</span> <span class="n">f</span> <span class="n">a</span><span class="o">)</span> <span class="o">:</span> <span class="n">deriv</span> <span class="n">f</span> <span class="n">a</span> <span class="bp">=</span> <span class="mi">0</span> <span class="o">:=</span> <span class="n">h.deriv_eq_zero</span> </pre></div> </div> <p>We can even state Rolle’s theorem without any differentiability assumptions, which seems even weirder.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span><span class="w"> </span><span class="n">Set</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span> <span class="n">Set</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hab</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hfc</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ContinuousOn</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">Icc</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="o">))</span><span class="w"> </span><span class="o">(</span><span class="n">hfI</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">Ioo</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="o">,</span><span class="w"> </span><span class="n">deriv</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">exists_deriv_eq_zero</span><span class="w"> </span><span class="n">hab</span><span class="w"> </span><span class="n">hfc</span><span class="w"> </span><span class="n">hfI</span> <span class="kd">example</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">{</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">hab</span> <span class="o">:</span> <span class="n">a</span> <span class="bp"><</span> <span class="n">b</span><span class="o">)</span> <span class="o">(</span><span class="n">hfc</span> <span class="o">:</span> <span class="n">ContinuousOn</span> <span class="n">f</span> <span class="o">(</span><span class="n">Icc</span> <span class="n">a</span> <span class="n">b</span><span class="o">))</span> <span class="o">(</span><span class="n">hfI</span> <span class="o">:</span> <span class="n">f</span> <span class="n">a</span> <span class="bp">=</span> <span class="n">f</span> <span class="n">b</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">c</span> <span class="bp">∈</span> <span class="n">Ioo</span> <span class="n">a</span> <span class="n">b</span><span class="o">,</span> <span class="n">deriv</span> <span class="n">f</span> <span class="n">c</span> <span class="bp">=</span> <span class="mi">0</span> <span class="o">:=</span> <span class="n">exists_deriv_eq_zero</span> <span class="n">hab</span> <span class="n">hfc</span> <span class="n">hfI</span> </pre></div> </div> <p>Of course, this trick does not work for the general mean value theorem.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hab</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ContinuousOn</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">Icc</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="o">))</span> <span class="w"> </span><span class="o">(</span><span class="n">hf'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">DifferentiableOn</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">Ioo</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="o">))</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">Ioo</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="o">,</span><span class="w"> </span><span class="n">deriv</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="o">(</span><span class="n">b</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">exists_deriv_eq_slope</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">hab</span><span class="w"> </span><span class="n">hf</span><span class="w"> </span><span class="n">hf'</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">{</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">hab</span> <span class="o">:</span> <span class="n">a</span> <span class="bp"><</span> <span class="n">b</span><span class="o">)</span> <span class="o">(</span><span class="n">hf</span> <span class="o">:</span> <span class="n">ContinuousOn</span> <span class="n">f</span> <span class="o">(</span><span class="n">Icc</span> <span class="n">a</span> <span class="n">b</span><span class="o">))</span> <span class="o">(</span><span class="n">hf'</span> <span class="o">:</span> <span class="n">DifferentiableOn</span> <span class="n">ℝ</span> <span class="n">f</span> <span class="o">(</span><span class="n">Ioo</span> <span class="n">a</span> <span class="n">b</span><span class="o">))</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">c</span> <span class="bp">∈</span> <span class="n">Ioo</span> <span class="n">a</span> <span class="n">b</span><span class="o">,</span> <span class="n">deriv</span> <span class="n">f</span> <span class="n">c</span> <span class="bp">=</span> <span class="o">(</span><span class="n">f</span> <span class="n">b</span> <span class="bp">-</span> <span class="n">f</span> <span class="n">a</span><span class="o">)</span> <span class="bp">/</span> <span class="o">(</span><span class="n">b</span> <span class="bp">-</span> <span class="n">a</span><span class="o">)</span> <span class="o">:=</span> <span class="n">exists_deriv_eq_slope</span> <span class="n">f</span> <span class="n">hab</span> <span class="n">hf</span> <span class="n">hf'</span> </pre></div> </div> <p>Lean can automatically compute some simple derivatives using the <code class="docutils literal notranslate"><span class="pre">simp</span></code> tactic.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">deriv</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">5</span><span class="o">)</span><span class="w"> </span><span class="mi">6</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="mi">6</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">4</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">simp</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">deriv</span> <span class="o">(</span><span class="k">fun</span> <span class="n">x</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">↦</span> <span class="n">x</span> <span class="bp">^</span> <span class="mi">5</span><span class="o">)</span> <span class="mi">6</span> <span class="bp">=</span> <span class="mi">5</span> <span class="bp">*</span> <span class="mi">6</span> <span class="bp">^</span> <span class="mi">4</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">deriv</span><span class="w"> </span><span class="n">sin</span><span class="w"> </span><span class="n">π</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">-</span><span class="mi">1</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">simp</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">deriv</span> <span class="n">sin</span> <span class="n">π</span> <span class="bp">=</span> <span class="bp">-</span><span class="mi">1</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">simp</span> </pre></div> </div> </section> <section id="differential-calculus-in-normed-spaces"> <span id="normed-spaces"></span><span id="index-2"></span><h2><span class="section-number">11.2. </span>Differential Calculus in Normed Spaces<a class="headerlink" href="#differential-calculus-in-normed-spaces" title="Link to this heading"></a></h2> <span id="normed-spaces"></span><span id="index-2"></span><h2><span class="section-number">11.2. </span>Differential Calculus in Normed Spaces<a class="headerlink" href="#differential-calculus-in-normed-spaces" title="Permalink to this heading"></a></h2> <section id="id3"> <h3><span class="section-number">11.2.1. </span>Normed spaces<a class="headerlink" href="#id3" title="Link to this heading"></a></h3> <h3><span class="section-number">11.2.1. </span>Normed spaces<a class="headerlink" href="#id3" title="Permalink to this heading"></a></h3> <p>Differentiation can be generalized beyond <code class="docutils literal notranslate"><span class="pre">ℝ</span></code> using the notion of a <em>normed vector space</em>, which encapsulates both direction and distance. We start with the notion of a <em>normed group</em>, which is an additive commutative group equipped with a real-valued norm function satisfying the following conditions.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">E</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">NormedAddCommGroup</span><span class="w"> </span><span class="n">E</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">E</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">NormedAddCommGroup</span> <span class="n">E</span><span class="o">]</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="bp">‖</span><span class="n">x</span><span class="bp">‖</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">norm_nonneg</span><span class="w"> </span><span class="n">x</span> <span class="kd">example</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">E</span><span class="o">)</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp">≤</span> <span class="bp">‖</span><span class="n">x</span><span class="bp">‖</span> <span class="o">:=</span> <span class="n">norm_nonneg</span> <span class="n">x</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="o">}</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">‖</span><span class="n">x</span><span class="bp">‖</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">norm_eq_zero</span> <span class="kd">example</span> <span class="o">{</span><span class="n">x</span> <span class="o">:</span> <span class="n">E</span><span class="o">}</span> <span class="o">:</span> <span class="bp">‖</span><span class="n">x</span><span class="bp">‖</span> <span class="bp">=</span> <span class="mi">0</span> <span class="bp">↔</span> <span class="n">x</span> <span class="bp">=</span> <span class="mi">0</span> <span class="o">:=</span> <span class="n">norm_eq_zero</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">‖</span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y</span><span class="bp">‖</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="bp">‖</span><span class="n">x</span><span class="bp">‖</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="bp">‖</span><span class="n">y</span><span class="bp">‖</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">norm_add_le</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span> <span class="kd">example</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">E</span><span class="o">)</span> <span class="o">:</span> <span class="bp">‖</span><span class="n">x</span> <span class="bp">+</span> <span class="n">y</span><span class="bp">‖</span> <span class="bp">≤</span> <span class="bp">‖</span><span class="n">x</span><span class="bp">‖</span> <span class="bp">+</span> <span class="bp">‖</span><span class="n">y</span><span class="bp">‖</span> <span class="o">:=</span> <span class="n">norm_add_le</span> <span class="n">x</span> <span class="n">y</span> </pre></div> </div> <p>Every normed space is a metric space with distance function <span class="math notranslate nohighlight">\(d(x, y) = \| x - y \|\)</span>, and hence it is also a topological space. Lean and Mathlib know this.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">MetricSpace</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">infer_instance</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">:</span> <span class="n">MetricSpace</span> <span class="n">E</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">infer_instance</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">X</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">TopologicalSpace</span><span class="w"> </span><span class="n">X</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">X</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">E</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Continuous</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">Continuous</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="bp">‖</span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="bp">‖</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">hf.norm</span> <span class="kd">example</span> <span class="o">{</span><span class="n">X</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">TopologicalSpace</span> <span class="n">X</span><span class="o">]</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">X</span> <span class="bp">→</span> <span class="n">E</span><span class="o">}</span> <span class="o">(</span><span class="n">hf</span> <span class="o">:</span> <span class="n">Continuous</span> <span class="n">f</span><span class="o">)</span> <span class="o">:</span> <span class="n">Continuous</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="bp">‖</span><span class="n">f</span> <span class="n">x</span><span class="bp">‖</span> <span class="o">:=</span> <span class="n">hf.norm</span> </pre></div> </div> <p>In order to use the notion of a norm with concepts from linear algebra, we add the assumption <code class="docutils literal notranslate"><span class="pre">NormedSpace</span> <span class="pre">ℝ</span> <span class="pre">E</span></code> on top of <code class="docutils literal notranslate"><span class="pre">NormedAddGroup</span> <span class="pre">E</span></code>. This stipulates that <code class="docutils literal notranslate"><span class="pre">E</span></code> is a vector space over <code class="docutils literal notranslate"><span class="pre">ℝ</span></code> and that scalar multiplication satisfies the following condition.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">[</span><span class="n">NormedSpace</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="n">E</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">[</span><span class="n">NormedSpace</span> <span class="n">ℝ</span> <span class="n">E</span><span class="o">]</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">‖</span><span class="n">a</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">x</span><span class="bp">‖</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">|</span><span class="n">a</span><span class="bp">|</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="bp">‖</span><span class="n">x</span><span class="bp">‖</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">norm_smul</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">x</span> <span class="kd">example</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">E</span><span class="o">)</span> <span class="o">:</span> <span class="bp">‖</span><span class="n">a</span> <span class="bp">•</span> <span class="n">x</span><span class="bp">‖</span> <span class="bp">=</span> <span class="bp">|</span><span class="n">a</span><span class="bp">|</span> <span class="bp">*</span> <span class="bp">‖</span><span class="n">x</span><span class="bp">‖</span> <span class="o">:=</span> <span class="n">norm_smul</span> <span class="n">a</span> <span class="n">x</span> </pre></div> </div> <p>A complete normed space is known as a <em>Banach space</em>. Every finite-dimensional vector space is complete.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">[</span><span class="n">FiniteDimensional</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="n">E</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">CompleteSpace</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">infer_instance</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">[</span><span class="n">FiniteDimensional</span> <span class="n">ℝ</span> <span class="n">E</span><span class="o">]</span> <span class="o">:</span> <span class="n">CompleteSpace</span> <span class="n">E</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">infer_instance</span> </pre></div> </div> <p>In all the previous examples, we used the real numbers as the base field.
-
@@ -234,23 +230,23 @@ More generally, we can make sense of calculus with a vector space over anyreal-valued norm that is multiplicative and has the property that not every element has norm zero or one (equivalently, there is an element whose norm is bigger than one).</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">𝕜</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">NontriviallyNormedField</span><span class="w"> </span><span class="n">𝕜</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">𝕜</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">‖</span><span class="n">x</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">y</span><span class="bp">‖</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">‖</span><span class="n">x</span><span class="bp">‖</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="bp">‖</span><span class="n">y</span><span class="bp">‖</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">norm_mul</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="bp">𝕜</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">)</span> <span class="o">[</span><span class="n">NontriviallyNormedField</span> <span class="bp">𝕜</span><span class="o">]</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="bp">𝕜</span><span class="o">)</span> <span class="o">:</span> <span class="bp">‖</span><span class="n">x</span> <span class="bp">*</span> <span class="n">y</span><span class="bp">‖</span> <span class="bp">=</span> <span class="bp">‖</span><span class="n">x</span><span class="bp">‖</span> <span class="bp">*</span> <span class="bp">‖</span><span class="n">y</span><span class="bp">‖</span> <span class="o">:=</span> <span class="n">norm_mul</span> <span class="n">x</span> <span class="n">y</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">𝕜</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">NontriviallyNormedField</span><span class="w"> </span><span class="n">𝕜</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">𝕜</span><span class="o">,</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="bp">‖</span><span class="n">x</span><span class="bp">‖</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">NormedField.exists_one_lt_norm</span><span class="w"> </span><span class="n">𝕜</span> <span class="kd">example</span> <span class="o">(</span><span class="bp">𝕜</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">)</span> <span class="o">[</span><span class="n">NontriviallyNormedField</span> <span class="bp">𝕜</span><span class="o">]</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">x</span> <span class="o">:</span> <span class="bp">𝕜</span><span class="o">,</span> <span class="mi">1</span> <span class="bp"><</span> <span class="bp">‖</span><span class="n">x</span><span class="bp">‖</span> <span class="o">:=</span> <span class="n">NormedField.exists_one_lt_norm</span> <span class="bp">𝕜</span> </pre></div> </div> <p>A finite-dimensional vector space over a nontrivially normed field is complete as long as the field itself is complete.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">𝕜</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">NontriviallyNormedField</span><span class="w"> </span><span class="n">𝕜</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">E</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">NormedAddCommGroup</span><span class="w"> </span><span class="n">E</span><span class="o">]</span> <span class="w"> </span><span class="o">[</span><span class="n">NormedSpace</span><span class="w"> </span><span class="n">𝕜</span><span class="w"> </span><span class="n">E</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">CompleteSpace</span><span class="w"> </span><span class="n">𝕜</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">FiniteDimensional</span><span class="w"> </span><span class="n">𝕜</span><span class="w"> </span><span class="n">E</span><span class="o">]</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">CompleteSpace</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">FiniteDimensional.complete</span><span class="w"> </span><span class="n">𝕜</span><span class="w"> </span><span class="n">E</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="bp">𝕜</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">)</span> <span class="o">[</span><span class="n">NontriviallyNormedField</span> <span class="bp">𝕜</span><span class="o">]</span> <span class="o">(</span><span class="n">E</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">)</span> <span class="o">[</span><span class="n">NormedAddCommGroup</span> <span class="n">E</span><span class="o">]</span> <span class="o">[</span><span class="n">NormedSpace</span> <span class="bp">𝕜</span> <span class="n">E</span><span class="o">]</span> <span class="o">[</span><span class="n">CompleteSpace</span> <span class="bp">𝕜</span><span class="o">]</span> <span class="o">[</span><span class="n">FiniteDimensional</span> <span class="bp">𝕜</span> <span class="n">E</span><span class="o">]</span> <span class="o">:</span> <span class="n">CompleteSpace</span> <span class="n">E</span> <span class="o">:=</span> <span class="n">FiniteDimensional.complete</span> <span class="bp">𝕜</span> <span class="n">E</span> </pre></div> </div> </section> <section id="continuous-linear-maps"> <h3><span class="section-number">11.2.2. </span>Continuous linear maps<a class="headerlink" href="#continuous-linear-maps" title="Link to this heading"></a></h3> <h3><span class="section-number">11.2.2. </span>Continuous linear maps<a class="headerlink" href="#continuous-linear-maps" title="Permalink to this heading"></a></h3> <p>We now turn to the morphisms in the category of normed spaces, namely, continuous linear maps. In Mathlib, the type of <code class="docutils literal notranslate"><span class="pre">𝕜</span></code>-linear continuous maps between normed spaces
-
@@ -260,34 +256,34 @@ a structure that that includes the function itself and the propertiesof being linear and continuous. Lean will insert a coercion so that a continuous linear map can be treated as a function.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">𝕜</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">NontriviallyNormedField</span><span class="w"> </span><span class="n">𝕜</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">E</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">NormedAddCommGroup</span><span class="w"> </span><span class="n">E</span><span class="o">]</span> <span class="w"> </span><span class="o">[</span><span class="n">NormedSpace</span><span class="w"> </span><span class="n">𝕜</span><span class="w"> </span><span class="n">E</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">F</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">NormedAddCommGroup</span><span class="w"> </span><span class="n">F</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">NormedSpace</span><span class="w"> </span><span class="n">𝕜</span><span class="w"> </span><span class="n">F</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="bp">𝕜</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">NontriviallyNormedField</span> <span class="bp">𝕜</span><span class="o">]</span> <span class="o">{</span><span class="n">E</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">NormedAddCommGroup</span> <span class="n">E</span><span class="o">]</span> <span class="o">[</span><span class="n">NormedSpace</span> <span class="bp">𝕜</span> <span class="n">E</span><span class="o">]</span> <span class="o">{</span><span class="n">F</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">NormedAddCommGroup</span> <span class="n">F</span><span class="o">]</span> <span class="o">[</span><span class="n">NormedSpace</span> <span class="bp">𝕜</span> <span class="n">F</span><span class="o">]</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="n">𝕜</span><span class="o">]</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">ContinuousLinearMap.id</span><span class="w"> </span><span class="n">𝕜</span><span class="w"> </span><span class="n">E</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">E</span> <span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="bp">𝕜</span><span class="o">]</span> <span class="n">E</span> <span class="o">:=</span> <span class="n">ContinuousLinearMap.id</span> <span class="bp">𝕜</span> <span class="n">E</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="n">𝕜</span><span class="o">]</span><span class="w"> </span><span class="n">F</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">f</span> <span class="kd">example</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">E</span> <span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="bp">𝕜</span><span class="o">]</span> <span class="n">F</span><span class="o">)</span> <span class="o">:</span> <span class="n">E</span> <span class="bp">→</span> <span class="n">F</span> <span class="o">:=</span> <span class="n">f</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="n">𝕜</span><span class="o">]</span><span class="w"> </span><span class="n">F</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Continuous</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">f.cont</span> <span class="kd">example</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">E</span> <span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="bp">𝕜</span><span class="o">]</span> <span class="n">F</span><span class="o">)</span> <span class="o">:</span> <span class="n">Continuous</span> <span class="n">f</span> <span class="o">:=</span> <span class="n">f.cont</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="n">𝕜</span><span class="o">]</span><span class="w"> </span><span class="n">F</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">f.map_add</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span> <span class="kd">example</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">E</span> <span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="bp">𝕜</span><span class="o">]</span> <span class="n">F</span><span class="o">)</span> <span class="o">(</span><span class="n">x</span> <span class="n">y</span> <span class="o">:</span> <span class="n">E</span><span class="o">)</span> <span class="o">:</span> <span class="n">f</span> <span class="o">(</span><span class="n">x</span> <span class="bp">+</span> <span class="n">y</span><span class="o">)</span> <span class="bp">=</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">+</span> <span class="n">f</span> <span class="n">y</span> <span class="o">:=</span> <span class="n">f.map_add</span> <span class="n">x</span> <span class="n">y</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="n">𝕜</span><span class="o">]</span><span class="w"> </span><span class="n">F</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">𝕜</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">f.map_smul</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">x</span> <span class="kd">example</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">E</span> <span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="bp">𝕜</span><span class="o">]</span> <span class="n">F</span><span class="o">)</span> <span class="o">(</span><span class="n">a</span> <span class="o">:</span> <span class="bp">𝕜</span><span class="o">)</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">E</span><span class="o">)</span> <span class="o">:</span> <span class="n">f</span> <span class="o">(</span><span class="n">a</span> <span class="bp">•</span> <span class="n">x</span><span class="o">)</span> <span class="bp">=</span> <span class="n">a</span> <span class="bp">•</span> <span class="n">f</span> <span class="n">x</span> <span class="o">:=</span> <span class="n">f.map_smul</span> <span class="n">a</span> <span class="n">x</span> </pre></div> </div> <p>Continuous linear maps have an operator norm that is characterized by the following properties.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="n">𝕜</span><span class="o">]</span><span class="w"> </span><span class="n">F</span><span class="o">)</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">E</span> <span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="bp">𝕜</span><span class="o">]</span> <span class="n">F</span><span class="o">)</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">‖</span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="bp">‖</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="bp">‖</span><span class="n">f</span><span class="bp">‖</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="bp">‖</span><span class="n">x</span><span class="bp">‖</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">f.le_opNorm</span><span class="w"> </span><span class="n">x</span> <span class="kd">example</span> <span class="o">(</span><span class="n">x</span> <span class="o">:</span> <span class="n">E</span><span class="o">)</span> <span class="o">:</span> <span class="bp">‖</span><span class="n">f</span> <span class="n">x</span><span class="bp">‖</span> <span class="bp">≤</span> <span class="bp">‖</span><span class="n">f</span><span class="bp">‖</span> <span class="bp">*</span> <span class="bp">‖</span><span class="n">x</span><span class="bp">‖</span> <span class="o">:=</span> <span class="n">f.le_opNorm</span> <span class="n">x</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">M</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hMp</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">M</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hM</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="bp">‖</span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="bp">‖</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="bp">‖</span><span class="n">x</span><span class="bp">‖</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">‖</span><span class="n">f</span><span class="bp">‖</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">M</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">f.opNorm_le_bound</span><span class="w"> </span><span class="n">hMp</span><span class="w"> </span><span class="n">hM</span> <span class="kd">example</span> <span class="o">{</span><span class="n">M</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">hMp</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp">≤</span> <span class="n">M</span><span class="o">)</span> <span class="o">(</span><span class="n">hM</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span><span class="o">,</span> <span class="bp">‖</span><span class="n">f</span> <span class="n">x</span><span class="bp">‖</span> <span class="bp">≤</span> <span class="n">M</span> <span class="bp">*</span> <span class="bp">‖</span><span class="n">x</span><span class="bp">‖</span><span class="o">)</span> <span class="o">:</span> <span class="bp">‖</span><span class="n">f</span><span class="bp">‖</span> <span class="bp">≤</span> <span class="n">M</span> <span class="o">:=</span> <span class="n">f.opNorm_le_bound</span> <span class="n">hMp</span> <span class="n">hM</span> </pre></div> </div> <p>There is also a notion of bundled continuous linear <em>isomorphism</em>.
-
@@ -301,82 +297,82 @@ The main ingredient is Baire’s theorem<code class="docutils literal notranslate"><span class="pre">nonempty_interior_of_iUnion_of_closed</span></code>. (You proved a version of this in the topology chapter.) Minor ingredients include <code class="docutils literal notranslate"><span class="pre">continuous_linear_map.opNorm_le_of_shell</span></code>, <code class="docutils literal notranslate"><span class="pre">interior_subset</span></code> and <code class="docutils literal notranslate"><span class="pre">interior_iInter_subset</span></code> and <code class="docutils literal notranslate"><span class="pre">isClosed_le</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">𝕜</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">NontriviallyNormedField</span><span class="w"> </span><span class="n">𝕜</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">E</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">NormedAddCommGroup</span><span class="w"> </span><span class="n">E</span><span class="o">]</span> <span class="w"> </span><span class="o">[</span><span class="n">NormedSpace</span><span class="w"> </span><span class="n">𝕜</span><span class="w"> </span><span class="n">E</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">F</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">NormedAddCommGroup</span><span class="w"> </span><span class="n">F</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">NormedSpace</span><span class="w"> </span><span class="n">𝕜</span><span class="w"> </span><span class="n">F</span><span class="o">]</span> <span class="kn">open</span><span class="w"> </span><span class="n">Metric</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">ι</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">CompleteSpace</span><span class="w"> </span><span class="n">E</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">g</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="n">𝕜</span><span class="o">]</span><span class="w"> </span><span class="n">F</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">C</span><span class="o">,</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="bp">‖</span><span class="n">g</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="n">x</span><span class="bp">‖</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">C</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">C'</span><span class="o">,</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="bp">‖</span><span class="n">g</span><span class="w"> </span><span class="n">i</span><span class="bp">‖</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">C'</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span> <span class="w"> </span><span class="c1">-- sequence of subsets consisting of those `x : E` with norms `‖g i x‖` bounded by `n`</span> <span class="w"> </span><span class="k">let</span><span class="w"> </span><span class="n">e</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="bp">⋂</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="o">,</span><span class="w"> </span><span class="o">{</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">|</span><span class="w"> </span><span class="bp">‖</span><span class="n">g</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="n">x</span><span class="bp">‖</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">}</span> <span class="w"> </span><span class="c1">-- each of these sets is closed</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">hc</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">,</span><span class="w"> </span><span class="n">IsClosed</span><span class="w"> </span><span class="o">(</span><span class="n">e</span><span class="w"> </span><span class="n">n</span><span class="o">)</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="c1">-- the union is the entire space; this is where we use `h`</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">hU</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="bp">⋃</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">,</span><span class="w"> </span><span class="n">e</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">univ</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="c">/-</span><span class="cm"> apply the Baire category theorem to conclude that for some `m : ℕ`,</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="bp">𝕜</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">NontriviallyNormedField</span> <span class="bp">𝕜</span><span class="o">]</span> <span class="o">{</span><span class="n">E</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">NormedAddCommGroup</span> <span class="n">E</span><span class="o">]</span> <span class="o">[</span><span class="n">NormedSpace</span> <span class="bp">𝕜</span> <span class="n">E</span><span class="o">]</span> <span class="o">{</span><span class="n">F</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">NormedAddCommGroup</span> <span class="n">F</span><span class="o">]</span> <span class="o">[</span><span class="n">NormedSpace</span> <span class="bp">𝕜</span> <span class="n">F</span><span class="o">]</span> <span class="kn">open</span> <span class="n">Metric</span> <span class="kd">example</span> <span class="o">{</span><span class="n">ι</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">CompleteSpace</span> <span class="n">E</span><span class="o">]</span> <span class="o">{</span><span class="n">g</span> <span class="o">:</span> <span class="n">ι</span> <span class="bp">→</span> <span class="n">E</span> <span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="bp">𝕜</span><span class="o">]</span> <span class="n">F</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span><span class="o">,</span> <span class="bp">∃</span> <span class="n">C</span><span class="o">,</span> <span class="bp">∀</span> <span class="n">i</span><span class="o">,</span> <span class="bp">‖</span><span class="n">g</span> <span class="n">i</span> <span class="n">x</span><span class="bp">‖</span> <span class="bp">≤</span> <span class="n">C</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">C'</span><span class="o">,</span> <span class="bp">∀</span> <span class="n">i</span><span class="o">,</span> <span class="bp">‖</span><span class="n">g</span> <span class="n">i</span><span class="bp">‖</span> <span class="bp">≤</span> <span class="n">C'</span> <span class="o">:=</span> <span class="kd">by</span> <span class="c1">-- sequence of subsets consisting of those `x : E` with norms `‖g i x‖` bounded by `n`</span> <span class="k">let</span> <span class="n">e</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">Set</span> <span class="n">E</span> <span class="o">:=</span> <span class="k">fun</span> <span class="n">n</span> <span class="bp">↦</span> <span class="bp">⋂</span> <span class="n">i</span> <span class="o">:</span> <span class="n">ι</span><span class="o">,</span> <span class="o">{</span> <span class="n">x</span> <span class="o">:</span> <span class="n">E</span> <span class="bp">|</span> <span class="bp">‖</span><span class="n">g</span> <span class="n">i</span> <span class="n">x</span><span class="bp">‖</span> <span class="bp">≤</span> <span class="n">n</span> <span class="o">}</span> <span class="c1">-- each of these sets is closed</span> <span class="k">have</span> <span class="n">hc</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">,</span> <span class="n">IsClosed</span> <span class="o">(</span><span class="n">e</span> <span class="n">n</span><span class="o">)</span> <span class="gr">sorry</span> <span class="c1">-- the union is the entire space; this is where we use `h`</span> <span class="k">have</span> <span class="n">hU</span> <span class="o">:</span> <span class="o">(</span><span class="bp">⋃</span> <span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">,</span> <span class="n">e</span> <span class="n">n</span><span class="o">)</span> <span class="bp">=</span> <span class="n">univ</span> <span class="gr">sorry</span> <span class="c">/-</span><span class="cm"> apply the Baire category theorem to conclude that for some `m : ℕ`,</span> <span class="cm"> `e m` contains some `x` -/</span> <span class="w"> </span><span class="n">obtain</span><span class="w"> </span><span class="o">⟨</span><span class="n">m</span><span class="o">,</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">hx</span><span class="o">⟩</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">m</span><span class="o">,</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">interior</span><span class="w"> </span><span class="o">(</span><span class="n">e</span><span class="w"> </span><span class="n">m</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">obtain</span><span class="w"> </span><span class="o">⟨</span><span class="n">ε</span><span class="o">,</span><span class="w"> </span><span class="n">ε_pos</span><span class="o">,</span><span class="w"> </span><span class="n">hε</span><span class="o">⟩</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span><span class="o">,</span><span class="w"> </span><span class="n">ball</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">interior</span><span class="w"> </span><span class="o">(</span><span class="n">e</span><span class="w"> </span><span class="n">m</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">obtain</span><span class="w"> </span><span class="o">⟨</span><span class="n">k</span><span class="o">,</span><span class="w"> </span><span class="n">hk</span><span class="o">⟩</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">k</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">𝕜</span><span class="o">,</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="bp">‖</span><span class="n">k</span><span class="bp">‖</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="c1">-- show all elements in the ball have norm bounded by `m` after applying any `g i`</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">real_norm_le</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">ball</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">ε</span><span class="o">,</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="o">(</span><span class="n">i</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="o">),</span><span class="w"> </span><span class="bp">‖</span><span class="n">g</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="n">z</span><span class="bp">‖</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">m</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="k">have</span><span class="w"> </span><span class="n">εk_pos</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">ε</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="bp">‖</span><span class="n">k</span><span class="bp">‖</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="n">refine</span><span class="w"> </span><span class="o">⟨(</span><span class="n">m</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="o">(</span><span class="n">ε</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="bp">‖</span><span class="n">k</span><span class="bp">‖</span><span class="o">),</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">ContinuousLinearMap.opNorm_le_of_shell</span><span class="w"> </span><span class="n">ε_pos</span><span class="w"> </span><span class="bp">?</span><span class="n">_</span><span class="w"> </span><span class="n">hk</span><span class="w"> </span><span class="bp">?</span><span class="n">_</span><span class="o">⟩</span> <span class="w"> </span><span class="gr">sorry</span> <span class="w"> </span><span class="gr">sorry</span> <span class="n">obtain</span> <span class="o">⟨</span><span class="n">m</span><span class="o">,</span> <span class="n">x</span><span class="o">,</span> <span class="n">hx</span><span class="o">⟩</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">m</span><span class="o">,</span> <span class="bp">∃</span> <span class="n">x</span><span class="o">,</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">interior</span> <span class="o">(</span><span class="n">e</span> <span class="n">m</span><span class="o">)</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="n">obtain</span> <span class="o">⟨</span><span class="n">ε</span><span class="o">,</span> <span class="n">ε_pos</span><span class="o">,</span> <span class="n">hε</span><span class="o">⟩</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">ε</span> <span class="bp">></span> <span class="mi">0</span><span class="o">,</span> <span class="n">ball</span> <span class="n">x</span> <span class="n">ε</span> <span class="bp">⊆</span> <span class="n">interior</span> <span class="o">(</span><span class="n">e</span> <span class="n">m</span><span class="o">)</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="n">obtain</span> <span class="o">⟨</span><span class="n">k</span><span class="o">,</span> <span class="n">hk</span><span class="o">⟩</span> <span class="o">:</span> <span class="bp">∃</span> <span class="n">k</span> <span class="o">:</span> <span class="bp">𝕜</span><span class="o">,</span> <span class="mi">1</span> <span class="bp"><</span> <span class="bp">‖</span><span class="n">k</span><span class="bp">‖</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="c1">-- show all elements in the ball have norm bounded by `m` after applying any `g i`</span> <span class="k">have</span> <span class="n">real_norm_le</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">z</span> <span class="bp">∈</span> <span class="n">ball</span> <span class="n">x</span> <span class="n">ε</span><span class="o">,</span> <span class="bp">∀</span> <span class="o">(</span><span class="n">i</span> <span class="o">:</span> <span class="n">ι</span><span class="o">),</span> <span class="bp">‖</span><span class="n">g</span> <span class="n">i</span> <span class="n">z</span><span class="bp">‖</span> <span class="bp">≤</span> <span class="n">m</span> <span class="gr">sorry</span> <span class="k">have</span> <span class="n">εk_pos</span> <span class="o">:</span> <span class="mi">0</span> <span class="bp"><</span> <span class="n">ε</span> <span class="bp">/</span> <span class="bp">‖</span><span class="n">k</span><span class="bp">‖</span> <span class="o">:=</span> <span class="gr">sorry</span> <span class="n">refine</span> <span class="o">⟨(</span><span class="n">m</span> <span class="bp">+</span> <span class="n">m</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="bp">/</span> <span class="o">(</span><span class="n">ε</span> <span class="bp">/</span> <span class="bp">‖</span><span class="n">k</span><span class="bp">‖</span><span class="o">),</span> <span class="k">fun</span> <span class="n">i</span> <span class="bp">↦</span> <span class="n">ContinuousLinearMap.opNorm_le_of_shell</span> <span class="n">ε_pos</span> <span class="bp">?</span><span class="n">_</span> <span class="n">hk</span> <span class="bp">?</span><span class="n">_</span><span class="o">⟩</span> <span class="gr">sorry</span> <span class="gr">sorry</span> </pre></div> </div> </section> <section id="asymptotic-comparisons"> <h3><span class="section-number">11.2.3. </span>Asymptotic comparisons<a class="headerlink" href="#asymptotic-comparisons" title="Link to this heading"></a></h3> <h3><span class="section-number">11.2.3. </span>Asymptotic comparisons<a class="headerlink" href="#asymptotic-comparisons" title="Permalink to this heading"></a></h3> <p>Defining differentiability also requires asymptotic comparisons. Mathlib has an extensive library covering the big O and little o relations, whose definitions are shown below. Opening the <code class="docutils literal notranslate"><span class="pre">asymptotics</span></code> locale allows us to use the corresponding notation. Here we will only use little o to define differentiability.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span><span class="w"> </span><span class="n">Asymptotics</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span> <span class="n">Asymptotics</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">E</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">NormedGroup</span><span class="w"> </span><span class="n">E</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">F</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">NormedGroup</span><span class="w"> </span><span class="n">F</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span> <span class="w"> </span><span class="o">(</span><span class="n">l</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Filter</span><span class="w"> </span><span class="n">α</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">E</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">g</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">F</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">IsBigOWith</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="n">l</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="bp">∀ᶠ</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">l</span><span class="o">,</span><span class="w"> </span><span class="bp">‖</span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="bp">‖</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="bp">‖</span><span class="n">g</span><span class="w"> </span><span class="n">x</span><span class="bp">‖</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">isBigOWith_iff</span> <span class="kd">example</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">{</span><span class="n">E</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">NormedGroup</span> <span class="n">E</span><span class="o">]</span> <span class="o">{</span><span class="n">F</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">NormedGroup</span> <span class="n">F</span><span class="o">]</span> <span class="o">(</span><span class="n">c</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">l</span> <span class="o">:</span> <span class="n">Filter</span> <span class="n">α</span><span class="o">)</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">E</span><span class="o">)</span> <span class="o">(</span><span class="n">g</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">F</span><span class="o">)</span> <span class="o">:</span> <span class="n">IsBigOWith</span> <span class="n">c</span> <span class="n">l</span> <span class="n">f</span> <span class="n">g</span> <span class="bp">↔</span> <span class="bp">∀ᶠ</span> <span class="n">x</span> <span class="k">in</span> <span class="n">l</span><span class="o">,</span> <span class="bp">‖</span><span class="n">f</span> <span class="n">x</span><span class="bp">‖</span> <span class="bp">≤</span> <span class="n">c</span> <span class="bp">*</span> <span class="bp">‖</span><span class="n">g</span> <span class="n">x</span><span class="bp">‖</span> <span class="o">:=</span> <span class="n">isBigOWith_iff</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">E</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">NormedGroup</span><span class="w"> </span><span class="n">E</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">F</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">NormedGroup</span><span class="w"> </span><span class="n">F</span><span class="o">]</span> <span class="w"> </span><span class="o">(</span><span class="n">l</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Filter</span><span class="w"> </span><span class="n">α</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">E</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">g</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">F</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">=</span><span class="n">O</span><span class="o">[</span><span class="n">l</span><span class="o">]</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="bp">∃</span><span class="w"> </span><span class="n">C</span><span class="o">,</span><span class="w"> </span><span class="n">IsBigOWith</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="n">l</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">isBigO_iff_isBigOWith</span> <span class="kd">example</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">{</span><span class="n">E</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">NormedGroup</span> <span class="n">E</span><span class="o">]</span> <span class="o">{</span><span class="n">F</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">NormedGroup</span> <span class="n">F</span><span class="o">]</span> <span class="o">(</span><span class="n">l</span> <span class="o">:</span> <span class="n">Filter</span> <span class="n">α</span><span class="o">)</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">E</span><span class="o">)</span> <span class="o">(</span><span class="n">g</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">F</span><span class="o">)</span> <span class="o">:</span> <span class="n">f</span> <span class="bp">=</span><span class="n">O</span><span class="o">[</span><span class="n">l</span><span class="o">]</span> <span class="n">g</span> <span class="bp">↔</span> <span class="bp">∃</span> <span class="n">C</span><span class="o">,</span> <span class="n">IsBigOWith</span> <span class="n">C</span> <span class="n">l</span> <span class="n">f</span> <span class="n">g</span> <span class="o">:=</span> <span class="n">isBigO_iff_isBigOWith</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">E</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">NormedGroup</span><span class="w"> </span><span class="n">E</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">F</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">NormedGroup</span><span class="w"> </span><span class="n">F</span><span class="o">]</span> <span class="w"> </span><span class="o">(</span><span class="n">l</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Filter</span><span class="w"> </span><span class="n">α</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">E</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">g</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">F</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">=</span><span class="n">o</span><span class="o">[</span><span class="n">l</span><span class="o">]</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="bp">></span><span class="w"> </span><span class="mi">0</span><span class="o">,</span><span class="w"> </span><span class="n">IsBigOWith</span><span class="w"> </span><span class="n">C</span><span class="w"> </span><span class="n">l</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">isLittleO_iff_forall_isBigOWith</span> <span class="kd">example</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">{</span><span class="n">E</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">NormedGroup</span> <span class="n">E</span><span class="o">]</span> <span class="o">{</span><span class="n">F</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">NormedGroup</span> <span class="n">F</span><span class="o">]</span> <span class="o">(</span><span class="n">l</span> <span class="o">:</span> <span class="n">Filter</span> <span class="n">α</span><span class="o">)</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">E</span><span class="o">)</span> <span class="o">(</span><span class="n">g</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">F</span><span class="o">)</span> <span class="o">:</span> <span class="n">f</span> <span class="bp">=</span><span class="n">o</span><span class="o">[</span><span class="n">l</span><span class="o">]</span> <span class="n">g</span> <span class="bp">↔</span> <span class="bp">∀</span> <span class="n">C</span> <span class="bp">></span> <span class="mi">0</span><span class="o">,</span> <span class="n">IsBigOWith</span> <span class="n">C</span> <span class="n">l</span> <span class="n">f</span> <span class="n">g</span> <span class="o">:=</span> <span class="n">isLittleO_iff_forall_isBigOWith</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">E</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">NormedAddCommGroup</span><span class="w"> </span><span class="n">E</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">l</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Filter</span><span class="w"> </span><span class="n">α</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">E</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">~</span><span class="o">[</span><span class="n">l</span><span class="o">]</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">g</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="n">o</span><span class="o">[</span><span class="n">l</span><span class="o">]</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Iff.rfl</span> <span class="kd">example</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">{</span><span class="n">E</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">NormedAddCommGroup</span> <span class="n">E</span><span class="o">]</span> <span class="o">(</span><span class="n">l</span> <span class="o">:</span> <span class="n">Filter</span> <span class="n">α</span><span class="o">)</span> <span class="o">(</span><span class="n">f</span> <span class="n">g</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">E</span><span class="o">)</span> <span class="o">:</span> <span class="n">f</span> <span class="bp">~</span><span class="o">[</span><span class="n">l</span><span class="o">]</span> <span class="n">g</span> <span class="bp">↔</span> <span class="o">(</span><span class="n">f</span> <span class="bp">-</span> <span class="n">g</span><span class="o">)</span> <span class="bp">=</span><span class="n">o</span><span class="o">[</span><span class="n">l</span><span class="o">]</span> <span class="n">g</span> <span class="o">:=</span> <span class="n">Iff.rfl</span> </pre></div> </div> </section> <section id="differentiability"> <h3><span class="section-number">11.2.4. </span>Differentiability<a class="headerlink" href="#differentiability" title="Link to this heading"></a></h3> <h3><span class="section-number">11.2.4. </span>Differentiability<a class="headerlink" href="#differentiability" title="Permalink to this heading"></a></h3> <p>We are now ready to discuss differentiable functions between normed spaces. In analogy the elementary one-dimensional, Mathlib defines a predicate <code class="docutils literal notranslate"><span class="pre">HasFDerivAt</span></code> and a function <code class="docutils literal notranslate"><span class="pre">fderiv</span></code>. Here the letter “f” stands for <em>Fréchet</em>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span><span class="w"> </span><span class="n">Topology</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span> <span class="n">Topology</span> <span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">𝕜</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">NontriviallyNormedField</span><span class="w"> </span><span class="n">𝕜</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">E</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">NormedAddCommGroup</span><span class="w"> </span><span class="n">E</span><span class="o">]</span> <span class="w"> </span><span class="o">[</span><span class="n">NormedSpace</span><span class="w"> </span><span class="n">𝕜</span><span class="w"> </span><span class="n">E</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">F</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">NormedAddCommGroup</span><span class="w"> </span><span class="n">F</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">NormedSpace</span><span class="w"> </span><span class="n">𝕜</span><span class="w"> </span><span class="n">F</span><span class="o">]</span> <span class="kd">variable</span> <span class="o">{</span><span class="bp">𝕜</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">NontriviallyNormedField</span> <span class="bp">𝕜</span><span class="o">]</span> <span class="o">{</span><span class="n">E</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">NormedAddCommGroup</span> <span class="n">E</span><span class="o">]</span> <span class="o">[</span><span class="n">NormedSpace</span> <span class="bp">𝕜</span> <span class="n">E</span><span class="o">]</span> <span class="o">{</span><span class="n">F</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">NormedAddCommGroup</span> <span class="n">F</span><span class="o">]</span> <span class="o">[</span><span class="n">NormedSpace</span> <span class="bp">𝕜</span> <span class="n">F</span><span class="o">]</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">F</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">f'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="n">𝕜</span><span class="o">]</span><span class="w"> </span><span class="n">F</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">x₀</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">HasFDerivAt</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">f'</span><span class="w"> </span><span class="n">x₀</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x₀</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">f'</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">x₀</span><span class="o">))</span><span class="w"> </span><span class="bp">=</span><span class="n">o</span><span class="o">[</span><span class="n">𝓝</span><span class="w"> </span><span class="n">x₀</span><span class="o">]</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">x₀</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">hasFDerivAtFilter_iff_isLittleO</span><span class="w"> </span><span class="bp">..</span> <span class="kd">example</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">E</span> <span class="bp">→</span> <span class="n">F</span><span class="o">)</span> <span class="o">(</span><span class="n">f'</span> <span class="o">:</span> <span class="n">E</span> <span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="bp">𝕜</span><span class="o">]</span> <span class="n">F</span><span class="o">)</span> <span class="o">(</span><span class="n">x₀</span> <span class="o">:</span> <span class="n">E</span><span class="o">)</span> <span class="o">:</span> <span class="n">HasFDerivAt</span> <span class="n">f</span> <span class="n">f'</span> <span class="n">x₀</span> <span class="bp">↔</span> <span class="o">(</span><span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">f</span> <span class="n">x</span> <span class="bp">-</span> <span class="n">f</span> <span class="n">x₀</span> <span class="bp">-</span> <span class="n">f'</span> <span class="o">(</span><span class="n">x</span> <span class="bp">-</span> <span class="n">x₀</span><span class="o">))</span> <span class="bp">=</span><span class="n">o</span><span class="o">[</span><span class="bp">𝓝</span> <span class="n">x₀</span><span class="o">]</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">x</span> <span class="bp">-</span> <span class="n">x₀</span> <span class="o">:=</span> <span class="n">hasFDerivAtFilter_iff_isLittleO</span> <span class="bp">..</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">F</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">f'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="n">𝕜</span><span class="o">]</span><span class="w"> </span><span class="n">F</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">x₀</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hff'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">HasFDerivAt</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">f'</span><span class="w"> </span><span class="n">x₀</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">fderiv</span><span class="w"> </span><span class="n">𝕜</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x₀</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">f'</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">hff'.fderiv</span> <span class="kd">example</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">E</span> <span class="bp">→</span> <span class="n">F</span><span class="o">)</span> <span class="o">(</span><span class="n">f'</span> <span class="o">:</span> <span class="n">E</span> <span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="bp">𝕜</span><span class="o">]</span> <span class="n">F</span><span class="o">)</span> <span class="o">(</span><span class="n">x₀</span> <span class="o">:</span> <span class="n">E</span><span class="o">)</span> <span class="o">(</span><span class="n">hff'</span> <span class="o">:</span> <span class="n">HasFDerivAt</span> <span class="n">f</span> <span class="n">f'</span> <span class="n">x₀</span><span class="o">)</span> <span class="o">:</span> <span class="n">fderiv</span> <span class="bp">𝕜</span> <span class="n">f</span> <span class="n">x₀</span> <span class="bp">=</span> <span class="n">f'</span> <span class="o">:=</span> <span class="n">hff'.fderiv</span> </pre></div> </div> <p>We also have iterated derivatives that take values in the type of multilinear maps
-
@@ -386,14 +382,14 @@ The type <code class="docutils literal notranslate"><span class="pre">WithTop</sis bigger than every natural number. So <span class="math notranslate nohighlight">\(\mathcal{C}^\infty\)</span> functions are functions <code class="docutils literal notranslate"><span class="pre">f</span></code> that satisfy <code class="docutils literal notranslate"><span class="pre">ContDiff</span> <span class="pre">𝕜</span> <span class="pre">⊤</span> <span class="pre">f</span></code>.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">F</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">E</span><span class="o">[</span><span class="bp">×</span><span class="n">n</span><span class="o">]</span><span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="n">𝕜</span><span class="o">]</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">iteratedFDeriv</span><span class="w"> </span><span class="n">𝕜</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">f</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">WithTop</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">F</span><span class="o">}</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">ContDiff</span><span class="w"> </span><span class="n">𝕜</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">↔</span> <span class="w"> </span><span class="o">(</span><span class="bp">∀</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">,</span><span class="w"> </span><span class="o">(</span><span class="n">m</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">WithTop</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Continuous</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">iteratedFDeriv</span><span class="w"> </span><span class="n">𝕜</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="bp">∧</span> <span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">,</span><span class="w"> </span><span class="o">(</span><span class="n">m</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">WithTop</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="bp"><</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Differentiable</span><span class="w"> </span><span class="n">𝕜</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">iteratedFDeriv</span><span class="w"> </span><span class="n">𝕜</span><span class="w"> </span><span class="n">m</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">contDiff_iff_continuous_differentiable</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">E</span> <span class="bp">→</span> <span class="n">F</span><span class="o">)</span> <span class="o">:</span> <span class="n">E</span> <span class="bp">→</span> <span class="n">E</span><span class="o">[</span><span class="bp">×</span><span class="n">n</span><span class="o">]</span><span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="bp">𝕜</span><span class="o">]</span> <span class="n">F</span> <span class="o">:=</span> <span class="n">iteratedFDeriv</span> <span class="bp">𝕜</span> <span class="n">n</span> <span class="n">f</span> <span class="kd">example</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">WithTop</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">E</span> <span class="bp">→</span> <span class="n">F</span><span class="o">}</span> <span class="o">:</span> <span class="n">ContDiff</span> <span class="bp">𝕜</span> <span class="n">n</span> <span class="n">f</span> <span class="bp">↔</span> <span class="o">(</span><span class="bp">∀</span> <span class="n">m</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">,</span> <span class="o">(</span><span class="n">m</span> <span class="o">:</span> <span class="n">WithTop</span> <span class="n">ℕ</span><span class="o">)</span> <span class="bp">≤</span> <span class="n">n</span> <span class="bp">→</span> <span class="n">Continuous</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">iteratedFDeriv</span> <span class="bp">𝕜</span> <span class="n">m</span> <span class="n">f</span> <span class="n">x</span><span class="o">)</span> <span class="bp">∧</span> <span class="bp">∀</span> <span class="n">m</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">,</span> <span class="o">(</span><span class="n">m</span> <span class="o">:</span> <span class="n">WithTop</span> <span class="n">ℕ</span><span class="o">)</span> <span class="bp"><</span> <span class="n">n</span> <span class="bp">→</span> <span class="n">Differentiable</span> <span class="bp">𝕜</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="n">iteratedFDeriv</span> <span class="bp">𝕜</span> <span class="n">m</span> <span class="n">f</span> <span class="n">x</span> <span class="o">:=</span> <span class="n">contDiff_iff_continuous_differentiable</span> </pre></div> </div> <p>There is a stricter notion of differentiability called
-
@@ -402,10 +398,10 @@ of the inverse function theorem and the statement of the implicit functiontheorem, both of which are in Mathlib. Over <code class="docutils literal notranslate"><span class="pre">ℝ</span></code> or <code class="docutils literal notranslate"><span class="pre">ℂ</span></code>, continuously differentiable functions are strictly differentiable.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">𝕂</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">RCLike</span><span class="w"> </span><span class="n">𝕂</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">E</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">NormedAddCommGroup</span><span class="w"> </span><span class="n">E</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">NormedSpace</span><span class="w"> </span><span class="n">𝕂</span><span class="w"> </span><span class="n">E</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">F</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="w"> </span><span class="o">[</span><span class="n">NormedAddCommGroup</span><span class="w"> </span><span class="n">F</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">NormedSpace</span><span class="w"> </span><span class="n">𝕂</span><span class="w"> </span><span class="n">F</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">F</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">WithTop</span><span class="w"> </span><span class="n">ℕ</span><span class="o">}</span> <span class="w"> </span><span class="o">(</span><span class="n">hf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ContDiffAt</span><span class="w"> </span><span class="n">𝕂</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hn</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">HasStrictFDerivAt</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">fderiv</span><span class="w"> </span><span class="n">𝕂</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">hf.hasStrictFDerivAt</span><span class="w"> </span><span class="n">hn</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="bp">𝕂</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">RCLike</span> <span class="bp">𝕂</span><span class="o">]</span> <span class="o">{</span><span class="n">E</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">NormedAddCommGroup</span> <span class="n">E</span><span class="o">]</span> <span class="o">[</span><span class="n">NormedSpace</span> <span class="bp">𝕂</span> <span class="n">E</span><span class="o">]</span> <span class="o">{</span><span class="n">F</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">NormedAddCommGroup</span> <span class="n">F</span><span class="o">]</span> <span class="o">[</span><span class="n">NormedSpace</span> <span class="bp">𝕂</span> <span class="n">F</span><span class="o">]</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">E</span> <span class="bp">→</span> <span class="n">F</span><span class="o">}</span> <span class="o">{</span><span class="n">x</span> <span class="o">:</span> <span class="n">E</span><span class="o">}</span> <span class="o">{</span><span class="n">n</span> <span class="o">:</span> <span class="n">WithTop</span> <span class="n">ℕ</span><span class="o">}</span> <span class="o">(</span><span class="n">hf</span> <span class="o">:</span> <span class="n">ContDiffAt</span> <span class="bp">𝕂</span> <span class="n">n</span> <span class="n">f</span> <span class="n">x</span><span class="o">)</span> <span class="o">(</span><span class="n">hn</span> <span class="o">:</span> <span class="mi">1</span> <span class="bp">≤</span> <span class="n">n</span><span class="o">)</span> <span class="o">:</span> <span class="n">HasStrictFDerivAt</span> <span class="n">f</span> <span class="o">(</span><span class="n">fderiv</span> <span class="bp">𝕂</span> <span class="n">f</span> <span class="n">x</span><span class="o">)</span> <span class="n">x</span> <span class="o">:=</span> <span class="n">hf.hasStrictFDerivAt</span> <span class="n">hn</span> </pre></div> </div> <p>The local inverse theorem is stated using an operation that produces an
-
@@ -415,26 +411,26 @@ point <code class="docutils literal notranslate"><span class="pre">a</span></cod<p>The first example below gets this local inverse. The next one states that it is indeed a local inverse from the left and from the right, and that it is strictly differentiable.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">section</span><span class="w"> </span><span class="n">LocalInverse</span> <span class="kd">variable</span><span class="w"> </span><span class="o">[</span><span class="n">CompleteSpace</span><span class="w"> </span><span class="n">E</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">F</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">f'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">≃</span><span class="n">L</span><span class="o">[</span><span class="n">𝕜</span><span class="o">]</span><span class="w"> </span><span class="n">F</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="o">}</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">section</span> <span class="n">LocalInverse</span> <span class="kd">variable</span> <span class="o">[</span><span class="n">CompleteSpace</span> <span class="n">E</span><span class="o">]</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">E</span> <span class="bp">→</span> <span class="n">F</span><span class="o">}</span> <span class="o">{</span><span class="n">f'</span> <span class="o">:</span> <span class="n">E</span> <span class="bp">≃</span><span class="n">L</span><span class="o">[</span><span class="bp">𝕜</span><span class="o">]</span> <span class="n">F</span><span class="o">}</span> <span class="o">{</span><span class="n">a</span> <span class="o">:</span> <span class="n">E</span><span class="o">}</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">hf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">HasStrictFDerivAt</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">f'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="n">𝕜</span><span class="o">]</span><span class="w"> </span><span class="n">F</span><span class="o">)</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">HasStrictFDerivAt.localInverse</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">f'</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">hf</span> <span class="kd">example</span> <span class="o">(</span><span class="n">hf</span> <span class="o">:</span> <span class="n">HasStrictFDerivAt</span> <span class="n">f</span> <span class="o">(</span><span class="n">f'</span> <span class="o">:</span> <span class="n">E</span> <span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="bp">𝕜</span><span class="o">]</span> <span class="n">F</span><span class="o">)</span> <span class="n">a</span><span class="o">)</span> <span class="o">:</span> <span class="n">F</span> <span class="bp">→</span> <span class="n">E</span> <span class="o">:=</span> <span class="n">HasStrictFDerivAt.localInverse</span> <span class="n">f</span> <span class="n">f'</span> <span class="n">a</span> <span class="n">hf</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">hf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">HasStrictFDerivAt</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">f'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="n">𝕜</span><span class="o">]</span><span class="w"> </span><span class="n">F</span><span class="o">)</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="bp">∀ᶠ</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">𝓝</span><span class="w"> </span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="n">hf.localInverse</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">f'</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">hf.eventually_left_inverse</span> <span class="kd">example</span> <span class="o">(</span><span class="n">hf</span> <span class="o">:</span> <span class="n">HasStrictFDerivAt</span> <span class="n">f</span> <span class="o">(</span><span class="n">f'</span> <span class="o">:</span> <span class="n">E</span> <span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="bp">𝕜</span><span class="o">]</span> <span class="n">F</span><span class="o">)</span> <span class="n">a</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∀ᶠ</span> <span class="n">x</span> <span class="k">in</span> <span class="bp">𝓝</span> <span class="n">a</span><span class="o">,</span> <span class="n">hf.localInverse</span> <span class="n">f</span> <span class="n">f'</span> <span class="n">a</span> <span class="o">(</span><span class="n">f</span> <span class="n">x</span><span class="o">)</span> <span class="bp">=</span> <span class="n">x</span> <span class="o">:=</span> <span class="n">hf.eventually_left_inverse</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">hf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">HasStrictFDerivAt</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">f'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="n">𝕜</span><span class="o">]</span><span class="w"> </span><span class="n">F</span><span class="o">)</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="bp">∀ᶠ</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">𝓝</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">a</span><span class="o">),</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">hf.localInverse</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">f'</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">hf.eventually_right_inverse</span> <span class="kd">example</span> <span class="o">(</span><span class="n">hf</span> <span class="o">:</span> <span class="n">HasStrictFDerivAt</span> <span class="n">f</span> <span class="o">(</span><span class="n">f'</span> <span class="o">:</span> <span class="n">E</span> <span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="bp">𝕜</span><span class="o">]</span> <span class="n">F</span><span class="o">)</span> <span class="n">a</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∀ᶠ</span> <span class="n">x</span> <span class="k">in</span> <span class="bp">𝓝</span> <span class="o">(</span><span class="n">f</span> <span class="n">a</span><span class="o">),</span> <span class="n">f</span> <span class="o">(</span><span class="n">hf.localInverse</span> <span class="n">f</span> <span class="n">f'</span> <span class="n">a</span> <span class="n">x</span><span class="o">)</span> <span class="bp">=</span> <span class="n">x</span> <span class="o">:=</span> <span class="n">hf.eventually_right_inverse</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">F</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">f'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">≃</span><span class="n">L</span><span class="o">[</span><span class="n">𝕜</span><span class="o">]</span><span class="w"> </span><span class="n">F</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="o">}</span> <span class="w"> </span><span class="o">(</span><span class="n">hf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">HasStrictFDerivAt</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">f'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="n">𝕜</span><span class="o">]</span><span class="w"> </span><span class="n">F</span><span class="o">)</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">HasStrictFDerivAt</span><span class="w"> </span><span class="o">(</span><span class="n">HasStrictFDerivAt.localInverse</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">f'</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">hf</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">f'.symm</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="n">𝕜</span><span class="o">]</span><span class="w"> </span><span class="n">E</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">HasStrictFDerivAt.to_localInverse</span><span class="w"> </span><span class="n">hf</span> <span class="kd">example</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">E</span> <span class="bp">→</span> <span class="n">F</span><span class="o">}</span> <span class="o">{</span><span class="n">f'</span> <span class="o">:</span> <span class="n">E</span> <span class="bp">≃</span><span class="n">L</span><span class="o">[</span><span class="bp">𝕜</span><span class="o">]</span> <span class="n">F</span><span class="o">}</span> <span class="o">{</span><span class="n">a</span> <span class="o">:</span> <span class="n">E</span><span class="o">}</span> <span class="o">(</span><span class="n">hf</span> <span class="o">:</span> <span class="n">HasStrictFDerivAt</span> <span class="n">f</span> <span class="o">(</span><span class="n">f'</span> <span class="o">:</span> <span class="n">E</span> <span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="bp">𝕜</span><span class="o">]</span> <span class="n">F</span><span class="o">)</span> <span class="n">a</span><span class="o">)</span> <span class="o">:</span> <span class="n">HasStrictFDerivAt</span> <span class="o">(</span><span class="n">HasStrictFDerivAt.localInverse</span> <span class="n">f</span> <span class="n">f'</span> <span class="n">a</span> <span class="n">hf</span><span class="o">)</span> <span class="o">(</span><span class="n">f'.symm</span> <span class="o">:</span> <span class="n">F</span> <span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="bp">𝕜</span><span class="o">]</span> <span class="n">E</span><span class="o">)</span> <span class="o">(</span><span class="n">f</span> <span class="n">a</span><span class="o">)</span> <span class="o">:=</span> <span class="n">HasStrictFDerivAt.to_localInverse</span> <span class="n">hf</span> <span class="kd">end</span><span class="w"> </span><span class="n">LocalInverse</span> <span class="kd">end</span> <span class="n">LocalInverse</span> </pre></div> </div> <p>This has been only a quick tour of the differential calculus in Mathlib.
-
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@@ -92,22 +88,22 @@<div role="main" class="document" itemscope="itemscope" itemtype="http://schema.org/Article"> <div itemprop="articleBody"> <section id="index-0"> <span id="integration-and-measure-theory"></span><span id="id1"></span><h1><span class="section-number">12. </span>Integration and Measure Theory<a class="headerlink" href="#index-0" title="Link to this heading"></a></h1> <span class="target" id="integration-and-measure-theory"></span><section id="index-0"> <span id="id1"></span><h1><span class="section-number">12. </span>Integration and Measure Theory<a class="headerlink" href="#index-0" title="Permalink to this heading"></a></h1> <section id="elementary-integration"> <span id="index-1"></span><span id="id2"></span><h2><span class="section-number">12.1. </span>Elementary Integration<a class="headerlink" href="#elementary-integration" title="Link to this heading"></a></h2> <span id="index-1"></span><span id="id2"></span><h2><span class="section-number">12.1. </span>Elementary Integration<a class="headerlink" href="#elementary-integration" title="Permalink to this heading"></a></h2> <p>We first focus on integration of functions on finite intervals in <code class="docutils literal notranslate"><span class="pre">ℝ</span></code>. We can integrate elementary functions.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span><span class="w"> </span><span class="n">MeasureTheory</span><span class="w"> </span><span class="n">intervalIntegral</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span> <span class="n">MeasureTheory</span> <span class="n">intervalIntegral</span> <span class="kn">open</span><span class="w"> </span><span class="n">Interval</span> <span class="kn">open</span> <span class="n">Interval</span> <span class="c1">-- this introduces the notation `[[a, b]]` for the segment from `min a b` to `max a b`</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="bp">∫</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">a</span><span class="bp">..</span><span class="n">b</span><span class="o">,</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">(</span><span class="n">b</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">^</span><span class="w"> </span><span class="mi">2</span><span class="o">)</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">integral_id</span> <span class="kd">example</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="bp">∫</span> <span class="n">x</span> <span class="k">in</span> <span class="n">a..b</span><span class="o">,</span> <span class="n">x</span><span class="o">)</span> <span class="bp">=</span> <span class="o">(</span><span class="n">b</span> <span class="bp">^</span> <span class="mi">2</span> <span class="bp">-</span> <span class="n">a</span> <span class="bp">^</span> <span class="mi">2</span><span class="o">)</span> <span class="bp">/</span> <span class="mi">2</span> <span class="o">:=</span> <span class="n">integral_id</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="mi">0</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="bp">∉</span><span class="w"> </span><span class="o">[[</span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="n">b</span><span class="o">]])</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="bp">∫</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">a</span><span class="bp">..</span><span class="n">b</span><span class="o">,</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">Real.log</span><span class="w"> </span><span class="o">(</span><span class="n">b</span><span class="w"> </span><span class="bp">/</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">integral_one_div</span><span class="w"> </span><span class="n">h</span> <span class="kd">example</span> <span class="o">{</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="o">(</span><span class="mi">0</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="bp">∉</span> <span class="o">[[</span><span class="n">a</span><span class="o">,</span> <span class="n">b</span><span class="o">]])</span> <span class="o">:</span> <span class="o">(</span><span class="bp">∫</span> <span class="n">x</span> <span class="k">in</span> <span class="n">a..b</span><span class="o">,</span> <span class="mi">1</span> <span class="bp">/</span> <span class="n">x</span><span class="o">)</span> <span class="bp">=</span> <span class="n">Real.log</span> <span class="o">(</span><span class="n">b</span> <span class="bp">/</span> <span class="n">a</span><span class="o">)</span> <span class="o">:=</span> <span class="n">integral_one_div</span> <span class="n">h</span> </pre></div> </div> <p>The fundamental theorem of calculus relates integration and differentiation.
-
@@ -116,25 +112,25 @@ says that integration provides an inverse to differentiation and the second onespecifies how to compute integrals of derivatives. (These two parts are very closely related, but their optimal versions, which are not shown here, are not equivalent.)</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Continuous</span><span class="w"> </span><span class="n">f</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">deriv</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="bp">∫</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">a</span><span class="bp">..</span><span class="n">u</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="o">(</span><span class="n">integral_hasStrictDerivAt_right</span><span class="w"> </span><span class="o">(</span><span class="n">hf.intervalIntegrable</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="n">_</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hf.stronglyMeasurableAtFilter</span><span class="w"> </span><span class="n">_</span><span class="w"> </span><span class="n">_</span><span class="o">)</span> <span class="w"> </span><span class="n">hf.continuousAt</span><span class="o">)</span><span class="bp">.</span><span class="n">hasDerivAt.deriv</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">hf</span> <span class="o">:</span> <span class="n">Continuous</span> <span class="n">f</span><span class="o">)</span> <span class="o">(</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="n">deriv</span> <span class="o">(</span><span class="k">fun</span> <span class="n">u</span> <span class="bp">↦</span> <span class="bp">∫</span> <span class="n">x</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="k">in</span> <span class="n">a..u</span><span class="o">,</span> <span class="n">f</span> <span class="n">x</span><span class="o">)</span> <span class="n">b</span> <span class="bp">=</span> <span class="n">f</span> <span class="n">b</span> <span class="o">:=</span> <span class="o">(</span><span class="n">integral_hasStrictDerivAt_right</span> <span class="o">(</span><span class="n">hf.intervalIntegrable</span> <span class="n">_</span> <span class="n">_</span><span class="o">)</span> <span class="o">(</span><span class="n">hf.stronglyMeasurableAtFilter</span> <span class="n">_</span> <span class="n">_</span><span class="o">)</span> <span class="n">hf.continuousAt</span><span class="o">)</span><span class="bp">.</span><span class="n">hasDerivAt.deriv</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">f'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="o">[[</span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="n">b</span><span class="o">]],</span><span class="w"> </span><span class="n">HasDerivAt</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">f'</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="n">x</span><span class="o">)</span> <span class="w"> </span><span class="o">(</span><span class="n">h'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">IntervalIntegrable</span><span class="w"> </span><span class="n">f'</span><span class="w"> </span><span class="n">volume</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="bp">∫</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">a</span><span class="bp">..</span><span class="n">b</span><span class="o">,</span><span class="w"> </span><span class="n">f'</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">integral_eq_sub_of_hasDerivAt</span><span class="w"> </span><span class="n">h</span><span class="w"> </span><span class="n">h'</span> <span class="kd">example</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">{</span><span class="n">a</span> <span class="n">b</span> <span class="o">:</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">{</span><span class="n">f'</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span> <span class="bp">∈</span> <span class="o">[[</span><span class="n">a</span><span class="o">,</span> <span class="n">b</span><span class="o">]],</span> <span class="n">HasDerivAt</span> <span class="n">f</span> <span class="o">(</span><span class="n">f'</span> <span class="n">x</span><span class="o">)</span> <span class="n">x</span><span class="o">)</span> <span class="o">(</span><span class="n">h'</span> <span class="o">:</span> <span class="n">IntervalIntegrable</span> <span class="n">f'</span> <span class="n">volume</span> <span class="n">a</span> <span class="n">b</span><span class="o">)</span> <span class="o">:</span> <span class="o">(</span><span class="bp">∫</span> <span class="n">y</span> <span class="k">in</span> <span class="n">a..b</span><span class="o">,</span> <span class="n">f'</span> <span class="n">y</span><span class="o">)</span> <span class="bp">=</span> <span class="n">f</span> <span class="n">b</span> <span class="bp">-</span> <span class="n">f</span> <span class="n">a</span> <span class="o">:=</span> <span class="n">integral_eq_sub_of_hasDerivAt</span> <span class="n">h</span> <span class="n">h'</span> </pre></div> </div> <p>Convolution is also defined in Mathlib and its basic properties are proved.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span><span class="w"> </span><span class="n">Convolution</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span> <span class="n">Convolution</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">g</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">⋆</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="bp">∫</span><span class="w"> </span><span class="n">t</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="bp">*</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">t</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">example</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">g</span> <span class="o">:</span> <span class="n">ℝ</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">:</span> <span class="n">f</span> <span class="bp">⋆</span> <span class="n">g</span> <span class="bp">=</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="bp">∫</span> <span class="n">t</span><span class="o">,</span> <span class="n">f</span> <span class="n">t</span> <span class="bp">*</span> <span class="n">g</span> <span class="o">(</span><span class="n">x</span> <span class="bp">-</span> <span class="n">t</span><span class="o">)</span> <span class="o">:=</span> <span class="n">rfl</span> </pre></div> </div> </section> <section id="measure-theory"> <span id="index-2"></span><span id="id3"></span><h2><span class="section-number">12.2. </span>Measure Theory<a class="headerlink" href="#measure-theory" title="Link to this heading"></a></h2> <span id="index-2"></span><span id="id3"></span><h2><span class="section-number">12.2. </span>Measure Theory<a class="headerlink" href="#measure-theory" title="Permalink to this heading"></a></h2> <p>The general context for integration in Mathlib is measure theory. Even the elementary integrals of the previous section are in fact Bochner integrals. Bochner integration is a generalization of Lebesgue integration where the target space can be any Banach space,
-
@@ -150,28 +146,28 @@ Note that these axioms are redundant; if you <code class="docutils literal notrayou will see the ones that Mathlib uses. As the examples below show, countability assumptions can be expressed using the <code class="docutils literal notranslate"><span class="pre">Encodable</span></code> type class.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">MeasurableSpace</span><span class="w"> </span><span class="n">α</span><span class="o">]</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">variable</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">MeasurableSpace</span> <span class="n">α</span><span class="o">]</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">MeasurableSet</span><span class="w"> </span><span class="o">(</span><span class="bp">∅</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">α</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">MeasurableSet.empty</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">MeasurableSet</span> <span class="o">(</span><span class="bp">∅</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">α</span><span class="o">)</span> <span class="o">:=</span> <span class="n">MeasurableSet.empty</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">MeasurableSet</span><span class="w"> </span><span class="o">(</span><span class="n">univ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">α</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">MeasurableSet.univ</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">MeasurableSet</span> <span class="o">(</span><span class="n">univ</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">α</span><span class="o">)</span> <span class="o">:=</span> <span class="n">MeasurableSet.univ</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">α</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hs</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">MeasurableSet</span><span class="w"> </span><span class="n">s</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">MeasurableSet</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="bp">ᶜ</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">hs.compl</span> <span class="kd">example</span> <span class="o">{</span><span class="n">s</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">α</span><span class="o">}</span> <span class="o">(</span><span class="n">hs</span> <span class="o">:</span> <span class="n">MeasurableSet</span> <span class="n">s</span><span class="o">)</span> <span class="o">:</span> <span class="n">MeasurableSet</span> <span class="o">(</span><span class="n">s</span><span class="bp">ᶜ</span><span class="o">)</span> <span class="o">:=</span> <span class="n">hs.compl</span> <span class="kd">example</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Encodable</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">infer_instance</span> <span class="kd">example</span> <span class="o">:</span> <span class="n">Encodable</span> <span class="n">ℕ</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">infer_instance</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Encodable</span><span class="w"> </span><span class="o">(</span><span class="n">Fin</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="kd">by</span><span class="w"> </span><span class="n">infer_instance</span> <span class="kd">example</span> <span class="o">(</span><span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span><span class="o">)</span> <span class="o">:</span> <span class="n">Encodable</span> <span class="o">(</span><span class="n">Fin</span> <span class="n">n</span><span class="o">)</span> <span class="o">:=</span> <span class="kd">by</span> <span class="n">infer_instance</span> <span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">ι</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">Encodable</span><span class="w"> </span><span class="n">ι</span><span class="o">]</span> <span class="kd">variable</span> <span class="o">{</span><span class="n">ι</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">Encodable</span> <span class="n">ι</span><span class="o">]</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">α</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">b</span><span class="o">,</span><span class="w"> </span><span class="n">MeasurableSet</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">b</span><span class="o">))</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">MeasurableSet</span><span class="w"> </span><span class="o">(</span><span class="bp">⋃</span><span class="w"> </span><span class="n">b</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">MeasurableSet.iUnion</span><span class="w"> </span><span class="n">h</span> <span class="kd">example</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">ι</span> <span class="bp">→</span> <span class="n">Set</span> <span class="n">α</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">b</span><span class="o">,</span> <span class="n">MeasurableSet</span> <span class="o">(</span><span class="n">f</span> <span class="n">b</span><span class="o">))</span> <span class="o">:</span> <span class="n">MeasurableSet</span> <span class="o">(</span><span class="bp">⋃</span> <span class="n">b</span><span class="o">,</span> <span class="n">f</span> <span class="n">b</span><span class="o">)</span> <span class="o">:=</span> <span class="n">MeasurableSet.iUnion</span> <span class="n">h</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">α</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">h</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">b</span><span class="o">,</span><span class="w"> </span><span class="n">MeasurableSet</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">b</span><span class="o">))</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">MeasurableSet</span><span class="w"> </span><span class="o">(</span><span class="bp">⋂</span><span class="w"> </span><span class="n">b</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">b</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">MeasurableSet.iInter</span><span class="w"> </span><span class="n">h</span> <span class="kd">example</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">ι</span> <span class="bp">→</span> <span class="n">Set</span> <span class="n">α</span><span class="o">}</span> <span class="o">(</span><span class="n">h</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">b</span><span class="o">,</span> <span class="n">MeasurableSet</span> <span class="o">(</span><span class="n">f</span> <span class="n">b</span><span class="o">))</span> <span class="o">:</span> <span class="n">MeasurableSet</span> <span class="o">(</span><span class="bp">⋂</span> <span class="n">b</span><span class="o">,</span> <span class="n">f</span> <span class="n">b</span><span class="o">)</span> <span class="o">:=</span> <span class="n">MeasurableSet.iInter</span> <span class="n">h</span> </pre></div> </div> <p>Once a type is measurable, we can measure it. On paper, a measure on a set
-
@@ -185,18 +181,18 @@ So we extend the measure to any set <code class="docutils literal notranslate"><as the infimum of measures of measurable sets containing <code class="docutils literal notranslate"><span class="pre">s</span></code>. Of course, many lemmas still require measurability assumptions, but not all.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span><span class="w"> </span><span class="n">MeasureTheory</span> <span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">μ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Measure</span><span class="w"> </span><span class="n">α</span><span class="o">}</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span> <span class="n">MeasureTheory</span> <span class="kd">variable</span> <span class="o">{</span><span class="n">μ</span> <span class="o">:</span> <span class="n">Measure</span> <span class="n">α</span><span class="o">}</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">α</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">μ</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">⨅</span><span class="w"> </span><span class="o">(</span><span class="n">t</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">α</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">_</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">⊆</span><span class="w"> </span><span class="n">t</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">_</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">MeasurableSet</span><span class="w"> </span><span class="n">t</span><span class="o">),</span><span class="w"> </span><span class="n">μ</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">measure_eq_iInf</span><span class="w"> </span><span class="n">s</span> <span class="kd">example</span> <span class="o">(</span><span class="n">s</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">α</span><span class="o">)</span> <span class="o">:</span> <span class="n">μ</span> <span class="n">s</span> <span class="bp">=</span> <span class="bp">⨅</span> <span class="o">(</span><span class="n">t</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">α</span><span class="o">)</span> <span class="o">(</span><span class="n">_</span> <span class="o">:</span> <span class="n">s</span> <span class="bp">⊆</span> <span class="n">t</span><span class="o">)</span> <span class="o">(</span><span class="n">_</span> <span class="o">:</span> <span class="n">MeasurableSet</span> <span class="n">t</span><span class="o">),</span> <span class="n">μ</span> <span class="n">t</span> <span class="o">:=</span> <span class="n">measure_eq_iInf</span> <span class="n">s</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ι</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">α</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">μ</span><span class="w"> </span><span class="o">(</span><span class="bp">⋃</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="bp">∑'</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">μ</span><span class="w"> </span><span class="o">(</span><span class="n">s</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">measure_iUnion_le</span><span class="w"> </span><span class="n">s</span> <span class="kd">example</span> <span class="o">(</span><span class="n">s</span> <span class="o">:</span> <span class="n">ι</span> <span class="bp">→</span> <span class="n">Set</span> <span class="n">α</span><span class="o">)</span> <span class="o">:</span> <span class="n">μ</span> <span class="o">(</span><span class="bp">⋃</span> <span class="n">i</span><span class="o">,</span> <span class="n">s</span> <span class="n">i</span><span class="o">)</span> <span class="bp">≤</span> <span class="bp">∑'</span> <span class="n">i</span><span class="o">,</span> <span class="n">μ</span> <span class="o">(</span><span class="n">s</span> <span class="n">i</span><span class="o">)</span> <span class="o">:=</span> <span class="n">measure_iUnion_le</span> <span class="n">s</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">α</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hmeas</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">MeasurableSet</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">i</span><span class="o">))</span><span class="w"> </span><span class="o">(</span><span class="n">hdis</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Pairwise</span><span class="w"> </span><span class="o">(</span><span class="n">Disjoint</span><span class="w"> </span><span class="n">on</span><span class="w"> </span><span class="n">f</span><span class="o">))</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">μ</span><span class="w"> </span><span class="o">(</span><span class="bp">⋃</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">∑'</span><span class="w"> </span><span class="n">i</span><span class="o">,</span><span class="w"> </span><span class="n">μ</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">i</span><span class="o">)</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">μ.m_iUnion</span><span class="w"> </span><span class="n">hmeas</span><span class="w"> </span><span class="n">hdis</span> <span class="kd">example</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">Set</span> <span class="n">α</span><span class="o">}</span> <span class="o">(</span><span class="n">hmeas</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">i</span><span class="o">,</span> <span class="n">MeasurableSet</span> <span class="o">(</span><span class="n">f</span> <span class="n">i</span><span class="o">))</span> <span class="o">(</span><span class="n">hdis</span> <span class="o">:</span> <span class="n">Pairwise</span> <span class="o">(</span><span class="n">Disjoint</span> <span class="n">on</span> <span class="n">f</span><span class="o">))</span> <span class="o">:</span> <span class="n">μ</span> <span class="o">(</span><span class="bp">⋃</span> <span class="n">i</span><span class="o">,</span> <span class="n">f</span> <span class="n">i</span><span class="o">)</span> <span class="bp">=</span> <span class="bp">∑'</span> <span class="n">i</span><span class="o">,</span> <span class="n">μ</span> <span class="o">(</span><span class="n">f</span> <span class="n">i</span><span class="o">)</span> <span class="o">:=</span> <span class="n">μ.m_iUnion</span> <span class="n">hmeas</span> <span class="n">hdis</span> </pre></div> </div> <p>Once a type has a measure associated with it, we say that a property <code class="docutils literal notranslate"><span class="pre">P</span></code>
-
@@ -205,13 +201,13 @@ has measure 0.The collection of properties that hold almost everywhere form a filter, but Mathlib introduces special notation for saying that a property holds almost everywhere.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">P</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="kt">Prop</span><span class="o">}</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="o">(</span><span class="bp">∀ᵐ</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∂</span><span class="n">μ</span><span class="o">,</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="bp">↔</span><span class="w"> </span><span class="bp">∀ᶠ</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">ae</span><span class="w"> </span><span class="n">μ</span><span class="o">,</span><span class="w"> </span><span class="n">P</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">Iff.rfl</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">P</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="kt">Prop</span><span class="o">}</span> <span class="o">:</span> <span class="o">(</span><span class="bp">∀ᵐ</span> <span class="n">x</span> <span class="bp">∂</span><span class="n">μ</span><span class="o">,</span> <span class="n">P</span> <span class="n">x</span><span class="o">)</span> <span class="bp">↔</span> <span class="bp">∀ᶠ</span> <span class="n">x</span> <span class="k">in</span> <span class="n">ae</span> <span class="n">μ</span><span class="o">,</span> <span class="n">P</span> <span class="n">x</span> <span class="o">:=</span> <span class="n">Iff.rfl</span> </pre></div> </div> </section> <section id="integration"> <span id="id4"></span><h2><span class="section-number">12.3. </span>Integration<a class="headerlink" href="#integration" title="Link to this heading"></a></h2> <span id="id4"></span><h2><span class="section-number">12.3. </span>Integration<a class="headerlink" href="#integration" title="Permalink to this heading"></a></h2> <p>Now that we have measurable spaces and measures we can consider integrals. As explained above, Mathlib uses a very general notion of integration that allows any Banach space as the target.
-
@@ -221,11 +217,11 @@ that an integral is equal to zero if the function in question isnot integrable. Most lemmas having to do with integrals have integrability assumptions.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">section</span> <span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">E</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">NormedAddCommGroup</span><span class="w"> </span><span class="n">E</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">NormedSpace</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="n">E</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">CompleteSpace</span><span class="w"> </span><span class="n">E</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">E</span><span class="o">}</span> <span class="kd">variable</span> <span class="o">{</span><span class="n">E</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">NormedAddCommGroup</span> <span class="n">E</span><span class="o">]</span> <span class="o">[</span><span class="n">NormedSpace</span> <span class="n">ℝ</span> <span class="n">E</span><span class="o">]</span> <span class="o">[</span><span class="n">CompleteSpace</span> <span class="n">E</span><span class="o">]</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">E</span><span class="o">}</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">E</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Integrable</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">μ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hg</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Integrable</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">μ</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="bp">∫</span><span class="w"> </span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">∂</span><span class="n">μ</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">∫</span><span class="w"> </span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">∂</span><span class="n">μ</span><span class="w"> </span><span class="bp">+</span><span class="w"> </span><span class="bp">∫</span><span class="w"> </span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">∂</span><span class="n">μ</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">integral_add</span><span class="w"> </span><span class="n">hf</span><span class="w"> </span><span class="n">hg</span> <span class="kd">example</span> <span class="o">{</span><span class="n">f</span> <span class="n">g</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">E</span><span class="o">}</span> <span class="o">(</span><span class="n">hf</span> <span class="o">:</span> <span class="n">Integrable</span> <span class="n">f</span> <span class="n">μ</span><span class="o">)</span> <span class="o">(</span><span class="n">hg</span> <span class="o">:</span> <span class="n">Integrable</span> <span class="n">g</span> <span class="n">μ</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∫</span> <span class="n">a</span><span class="o">,</span> <span class="n">f</span> <span class="n">a</span> <span class="bp">+</span> <span class="n">g</span> <span class="n">a</span> <span class="bp">∂</span><span class="n">μ</span> <span class="bp">=</span> <span class="bp">∫</span> <span class="n">a</span><span class="o">,</span> <span class="n">f</span> <span class="n">a</span> <span class="bp">∂</span><span class="n">μ</span> <span class="bp">+</span> <span class="bp">∫</span> <span class="n">a</span><span class="o">,</span> <span class="n">g</span> <span class="n">a</span> <span class="bp">∂</span><span class="n">μ</span> <span class="o">:=</span> <span class="n">integral_add</span> <span class="n">hf</span> <span class="n">hg</span> </pre></div> </div> <p>As an example of the complex interactions between our various conventions, let us see how to integrate constant functions.
-
@@ -235,41 +231,41 @@ the point at infinity, to zero.For any <code class="docutils literal notranslate"><span class="pre">s</span> <span class="pre">:</span> <span class="pre">Set</span> <span class="pre">α</span></code>, if <code class="docutils literal notranslate"><span class="pre">μ</span> <span class="pre">s</span> <span class="pre">=</span> <span class="pre">⊤</span></code>, then nonzero constant functions are not integrable on <code class="docutils literal notranslate"><span class="pre">s</span></code>. In that case, their integrals are equal to zero by definition, as is <code class="docutils literal notranslate"><span class="pre">(μ</span> <span class="pre">s).toReal</span></code>. So in all cases we have the following lemma.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">α</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">c</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="o">)</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∫</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="bp">∂</span><span class="n">μ</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="o">(</span><span class="n">μ</span><span class="w"> </span><span class="n">s</span><span class="o">)</span><span class="bp">.</span><span class="n">toReal</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">setIntegral_const</span><span class="w"> </span><span class="n">c</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">s</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">α</span><span class="o">}</span> <span class="o">(</span><span class="n">c</span> <span class="o">:</span> <span class="n">E</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∫</span> <span class="n">x</span> <span class="k">in</span> <span class="n">s</span><span class="o">,</span> <span class="n">c</span> <span class="bp">∂</span><span class="n">μ</span> <span class="bp">=</span> <span class="o">(</span><span class="n">μ</span> <span class="n">s</span><span class="o">)</span><span class="bp">.</span><span class="n">toReal</span> <span class="bp">•</span> <span class="n">c</span> <span class="o">:=</span> <span class="n">setIntegral_const</span> <span class="n">c</span> </pre></div> </div> <p>We now quickly explain how to access the most important theorems in integration theory, starting with the dominated convergence theorem. There are several versions in Mathlib, and here we only show the most basic one.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span><span class="w"> </span><span class="n">Filter</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span> <span class="n">Filter</span> <span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">F</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">E</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">E</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">bound</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">ℝ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hmeas</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="n">AEStronglyMeasurable</span><span class="w"> </span><span class="o">(</span><span class="n">F</span><span class="w"> </span><span class="n">n</span><span class="o">)</span><span class="w"> </span><span class="n">μ</span><span class="o">)</span> <span class="w"> </span><span class="o">(</span><span class="n">hint</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Integrable</span><span class="w"> </span><span class="n">bound</span><span class="w"> </span><span class="n">μ</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">hbound</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">n</span><span class="o">,</span><span class="w"> </span><span class="bp">∀ᵐ</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">∂</span><span class="n">μ</span><span class="o">,</span><span class="w"> </span><span class="bp">‖</span><span class="n">F</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">a</span><span class="bp">‖</span><span class="w"> </span><span class="bp">≤</span><span class="w"> </span><span class="n">bound</span><span class="w"> </span><span class="n">a</span><span class="o">)</span> <span class="w"> </span><span class="o">(</span><span class="n">hlim</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀ᵐ</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">∂</span><span class="n">μ</span><span class="o">,</span><span class="w"> </span><span class="n">Tendsto</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">ℕ</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">a</span><span class="o">)</span><span class="w"> </span><span class="n">atTop</span><span class="w"> </span><span class="o">(</span><span class="n">𝓝</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">a</span><span class="o">)))</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">Tendsto</span><span class="w"> </span><span class="o">(</span><span class="k">fun</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="bp">∫</span><span class="w"> </span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="n">n</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">∂</span><span class="n">μ</span><span class="o">)</span><span class="w"> </span><span class="n">atTop</span><span class="w"> </span><span class="o">(</span><span class="n">𝓝</span><span class="w"> </span><span class="o">(</span><span class="bp">∫</span><span class="w"> </span><span class="n">a</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="bp">∂</span><span class="n">μ</span><span class="o">))</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">tendsto_integral_of_dominated_convergence</span><span class="w"> </span><span class="n">bound</span><span class="w"> </span><span class="n">hmeas</span><span class="w"> </span><span class="n">hint</span><span class="w"> </span><span class="n">hbound</span><span class="w"> </span><span class="n">hlim</span> <span class="kd">example</span> <span class="o">{</span><span class="n">F</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">→</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">E</span><span class="o">}</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">E</span><span class="o">}</span> <span class="o">(</span><span class="n">bound</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">→</span> <span class="n">ℝ</span><span class="o">)</span> <span class="o">(</span><span class="n">hmeas</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">n</span><span class="o">,</span> <span class="n">AEStronglyMeasurable</span> <span class="o">(</span><span class="n">F</span> <span class="n">n</span><span class="o">)</span> <span class="n">μ</span><span class="o">)</span> <span class="o">(</span><span class="n">hint</span> <span class="o">:</span> <span class="n">Integrable</span> <span class="n">bound</span> <span class="n">μ</span><span class="o">)</span> <span class="o">(</span><span class="n">hbound</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">n</span><span class="o">,</span> <span class="bp">∀ᵐ</span> <span class="n">a</span> <span class="bp">∂</span><span class="n">μ</span><span class="o">,</span> <span class="bp">‖</span><span class="n">F</span> <span class="n">n</span> <span class="n">a</span><span class="bp">‖</span> <span class="bp">≤</span> <span class="n">bound</span> <span class="n">a</span><span class="o">)</span> <span class="o">(</span><span class="n">hlim</span> <span class="o">:</span> <span class="bp">∀ᵐ</span> <span class="n">a</span> <span class="bp">∂</span><span class="n">μ</span><span class="o">,</span> <span class="n">Tendsto</span> <span class="o">(</span><span class="k">fun</span> <span class="n">n</span> <span class="o">:</span> <span class="n">ℕ</span> <span class="bp">↦</span> <span class="n">F</span> <span class="n">n</span> <span class="n">a</span><span class="o">)</span> <span class="n">atTop</span> <span class="o">(</span><span class="bp">𝓝</span> <span class="o">(</span><span class="n">f</span> <span class="n">a</span><span class="o">)))</span> <span class="o">:</span> <span class="n">Tendsto</span> <span class="o">(</span><span class="k">fun</span> <span class="n">n</span> <span class="bp">↦</span> <span class="bp">∫</span> <span class="n">a</span><span class="o">,</span> <span class="n">F</span> <span class="n">n</span> <span class="n">a</span> <span class="bp">∂</span><span class="n">μ</span><span class="o">)</span> <span class="n">atTop</span> <span class="o">(</span><span class="bp">𝓝</span> <span class="o">(</span><span class="bp">∫</span> <span class="n">a</span><span class="o">,</span> <span class="n">f</span> <span class="n">a</span> <span class="bp">∂</span><span class="n">μ</span><span class="o">))</span> <span class="o">:=</span> <span class="n">tendsto_integral_of_dominated_convergence</span> <span class="n">bound</span> <span class="n">hmeas</span> <span class="n">hint</span> <span class="n">hbound</span> <span class="n">hlim</span> </pre></div> </div> <p>Then we have Fubini’s theorem for integrals on product type.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">α</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">MeasurableSpace</span><span class="w"> </span><span class="n">α</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">μ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Measure</span><span class="w"> </span><span class="n">α</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">SigmaFinite</span><span class="w"> </span><span class="n">μ</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">β</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="w"> </span><span class="o">[</span><span class="n">MeasurableSpace</span><span class="w"> </span><span class="n">β</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">ν</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Measure</span><span class="w"> </span><span class="n">β</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">SigmaFinite</span><span class="w"> </span><span class="n">ν</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">α</span><span class="w"> </span><span class="bp">×</span><span class="w"> </span><span class="n">β</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">E</span><span class="o">)</span> <span class="w"> </span><span class="o">(</span><span class="n">hf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Integrable</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">μ.prod</span><span class="w"> </span><span class="n">ν</span><span class="o">))</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∫</span><span class="w"> </span><span class="n">z</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="bp">∂</span><span class="w"> </span><span class="n">μ.prod</span><span class="w"> </span><span class="n">ν</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">∫</span><span class="w"> </span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="bp">∫</span><span class="w"> </span><span class="n">y</span><span class="o">,</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="o">,</span><span class="w"> </span><span class="n">y</span><span class="o">)</span><span class="w"> </span><span class="bp">∂</span><span class="n">ν</span><span class="w"> </span><span class="bp">∂</span><span class="n">μ</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">integral_prod</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">hf</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">α</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">MeasurableSpace</span> <span class="n">α</span><span class="o">]</span> <span class="o">{</span><span class="n">μ</span> <span class="o">:</span> <span class="n">Measure</span> <span class="n">α</span><span class="o">}</span> <span class="o">[</span><span class="n">SigmaFinite</span> <span class="n">μ</span><span class="o">]</span> <span class="o">{</span><span class="n">β</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">MeasurableSpace</span> <span class="n">β</span><span class="o">]</span> <span class="o">{</span><span class="n">ν</span> <span class="o">:</span> <span class="n">Measure</span> <span class="n">β</span><span class="o">}</span> <span class="o">[</span><span class="n">SigmaFinite</span> <span class="n">ν</span><span class="o">]</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">α</span> <span class="bp">×</span> <span class="n">β</span> <span class="bp">→</span> <span class="n">E</span><span class="o">)</span> <span class="o">(</span><span class="n">hf</span> <span class="o">:</span> <span class="n">Integrable</span> <span class="n">f</span> <span class="o">(</span><span class="n">μ.prod</span> <span class="n">ν</span><span class="o">))</span> <span class="o">:</span> <span class="bp">∫</span> <span class="n">z</span><span class="o">,</span> <span class="n">f</span> <span class="n">z</span> <span class="bp">∂</span> <span class="n">μ.prod</span> <span class="n">ν</span> <span class="bp">=</span> <span class="bp">∫</span> <span class="n">x</span><span class="o">,</span> <span class="bp">∫</span> <span class="n">y</span><span class="o">,</span> <span class="n">f</span> <span class="o">(</span><span class="n">x</span><span class="o">,</span> <span class="n">y</span><span class="o">)</span> <span class="bp">∂</span><span class="n">ν</span> <span class="bp">∂</span><span class="n">μ</span> <span class="o">:=</span> <span class="n">integral_prod</span> <span class="n">f</span> <span class="n">hf</span> </pre></div> </div> <p>There is a very general version of convolution that applies to any continuous bilinear form.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span><span class="w"> </span><span class="n">Convolution</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kn">open</span> <span class="n">Convolution</span> <span class="kd">variable</span><span class="w"> </span><span class="o">{</span><span class="n">𝕜</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">G</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">E</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">E'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">F</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">NormedAddCommGroup</span><span class="w"> </span><span class="n">E</span><span class="o">]</span> <span class="w"> </span><span class="o">[</span><span class="n">NormedAddCommGroup</span><span class="w"> </span><span class="n">E'</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">NormedAddCommGroup</span><span class="w"> </span><span class="n">F</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">NontriviallyNormedField</span><span class="w"> </span><span class="n">𝕜</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">NormedSpace</span><span class="w"> </span><span class="n">𝕜</span><span class="w"> </span><span class="n">E</span><span class="o">]</span> <span class="w"> </span><span class="o">[</span><span class="n">NormedSpace</span><span class="w"> </span><span class="n">𝕜</span><span class="w"> </span><span class="n">E'</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">NormedSpace</span><span class="w"> </span><span class="n">𝕜</span><span class="w"> </span><span class="n">F</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">MeasurableSpace</span><span class="w"> </span><span class="n">G</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">NormedSpace</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="n">F</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">CompleteSpace</span><span class="w"> </span><span class="n">F</span><span class="o">]</span> <span class="w"> </span><span class="o">[</span><span class="n">Sub</span><span class="w"> </span><span class="n">G</span><span class="o">]</span> <span class="kd">variable</span> <span class="o">{</span><span class="bp">𝕜</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">{</span><span class="n">G</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">{</span><span class="n">E</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">{</span><span class="n">E'</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">{</span><span class="n">F</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">NormedAddCommGroup</span> <span class="n">E</span><span class="o">]</span> <span class="o">[</span><span class="n">NormedAddCommGroup</span> <span class="n">E'</span><span class="o">]</span> <span class="o">[</span><span class="n">NormedAddCommGroup</span> <span class="n">F</span><span class="o">]</span> <span class="o">[</span><span class="n">NontriviallyNormedField</span> <span class="bp">𝕜</span><span class="o">]</span> <span class="o">[</span><span class="n">NormedSpace</span> <span class="bp">𝕜</span> <span class="n">E</span><span class="o">]</span> <span class="o">[</span><span class="n">NormedSpace</span> <span class="bp">𝕜</span> <span class="n">E'</span><span class="o">]</span> <span class="o">[</span><span class="n">NormedSpace</span> <span class="bp">𝕜</span> <span class="n">F</span><span class="o">]</span> <span class="o">[</span><span class="n">MeasurableSpace</span> <span class="n">G</span><span class="o">]</span> <span class="o">[</span><span class="n">NormedSpace</span> <span class="n">ℝ</span> <span class="n">F</span><span class="o">]</span> <span class="o">[</span><span class="n">CompleteSpace</span> <span class="n">F</span><span class="o">]</span> <span class="o">[</span><span class="n">Sub</span> <span class="n">G</span><span class="o">]</span> <span class="kd">example</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">E</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">g</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">E'</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">L</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="n">𝕜</span><span class="o">]</span><span class="w"> </span><span class="n">E'</span><span class="w"> </span><span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="n">𝕜</span><span class="o">]</span><span class="w"> </span><span class="n">F</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">μ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Measure</span><span class="w"> </span><span class="n">G</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">⋆</span><span class="o">[</span><span class="n">L</span><span class="o">,</span><span class="w"> </span><span class="n">μ</span><span class="o">]</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">↦</span><span class="w"> </span><span class="bp">∫</span><span class="w"> </span><span class="n">t</span><span class="o">,</span><span class="w"> </span><span class="n">L</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">t</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">g</span><span class="w"> </span><span class="o">(</span><span class="n">x</span><span class="w"> </span><span class="bp">-</span><span class="w"> </span><span class="n">t</span><span class="o">))</span><span class="w"> </span><span class="bp">∂</span><span class="n">μ</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">rfl</span> <span class="kd">example</span> <span class="o">(</span><span class="n">f</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">→</span> <span class="n">E</span><span class="o">)</span> <span class="o">(</span><span class="n">g</span> <span class="o">:</span> <span class="n">G</span> <span class="bp">→</span> <span class="n">E'</span><span class="o">)</span> <span class="o">(</span><span class="n">L</span> <span class="o">:</span> <span class="n">E</span> <span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="bp">𝕜</span><span class="o">]</span> <span class="n">E'</span> <span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="bp">𝕜</span><span class="o">]</span> <span class="n">F</span><span class="o">)</span> <span class="o">(</span><span class="n">μ</span> <span class="o">:</span> <span class="n">Measure</span> <span class="n">G</span><span class="o">)</span> <span class="o">:</span> <span class="n">f</span> <span class="bp">⋆</span><span class="o">[</span><span class="n">L</span><span class="o">,</span> <span class="n">μ</span><span class="o">]</span> <span class="n">g</span> <span class="bp">=</span> <span class="k">fun</span> <span class="n">x</span> <span class="bp">↦</span> <span class="bp">∫</span> <span class="n">t</span><span class="o">,</span> <span class="n">L</span> <span class="o">(</span><span class="n">f</span> <span class="n">t</span><span class="o">)</span> <span class="o">(</span><span class="n">g</span> <span class="o">(</span><span class="n">x</span> <span class="bp">-</span> <span class="n">t</span><span class="o">))</span> <span class="bp">∂</span><span class="n">μ</span> <span class="o">:=</span> <span class="n">rfl</span> </pre></div> </div> <p>Finally, Mathlib has a very general version of the change-of-variables formula.
-
@@ -277,13 +273,13 @@ In the statement below, <code class="docutils literal notranslate"><span class="<span class="math notranslate nohighlight">\(\sigma\)</span>-algebra on <code class="docutils literal notranslate"><span class="pre">E</span></code> is generated by the open sets of <code class="docutils literal notranslate"><span class="pre">E</span></code>, and <code class="docutils literal notranslate"><span class="pre">IsAddHaarMeasure</span> <span class="pre">μ</span></code> means that the measure <code class="docutils literal notranslate"><span class="pre">μ</span></code> is left-invariant, gives finite mass to compact sets, and give positive mass to open sets.</p> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span><span class="w"> </span><span class="o">{</span><span class="n">E</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span><span class="w"> </span><span class="o">[</span><span class="n">NormedAddCommGroup</span><span class="w"> </span><span class="n">E</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">NormedSpace</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="n">E</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">FiniteDimensional</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="n">E</span><span class="o">]</span> <span class="w"> </span><span class="o">[</span><span class="n">MeasurableSpace</span><span class="w"> </span><span class="n">E</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">BorelSpace</span><span class="w"> </span><span class="n">E</span><span class="o">]</span><span class="w"> </span><span class="o">(</span><span class="n">μ</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Measure</span><span class="w"> </span><span class="n">E</span><span class="o">)</span><span class="w"> </span><span class="o">[</span><span class="n">μ.IsAddHaarMeasure</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">F</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="w"> </span><span class="o">[</span><span class="n">NormedAddCommGroup</span><span class="w"> </span><span class="n">F</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">NormedSpace</span><span class="w"> </span><span class="n">ℝ</span><span class="w"> </span><span class="n">F</span><span class="o">]</span><span class="w"> </span><span class="o">[</span><span class="n">CompleteSpace</span><span class="w"> </span><span class="n">F</span><span class="o">]</span><span class="w"> </span><span class="o">{</span><span class="n">s</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">Set</span><span class="w"> </span><span class="n">E</span><span class="o">}</span><span class="w"> </span><span class="o">{</span><span class="n">f</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">E</span><span class="o">}</span> <span class="w"> </span><span class="o">{</span><span class="n">f'</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="n">ℝ</span><span class="o">]</span><span class="w"> </span><span class="n">E</span><span class="o">}</span><span class="w"> </span><span class="o">(</span><span class="n">hs</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">MeasurableSet</span><span class="w"> </span><span class="n">s</span><span class="o">)</span> <span class="w"> </span><span class="o">(</span><span class="n">hf</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="bp">∀</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="o">,</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∈</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">HasFDerivWithinAt</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="o">(</span><span class="n">f'</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">h_inj</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">InjOn</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">s</span><span class="o">)</span><span class="w"> </span><span class="o">(</span><span class="n">g</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">E</span><span class="w"> </span><span class="bp">→</span><span class="w"> </span><span class="n">F</span><span class="o">)</span><span class="w"> </span><span class="o">:</span> <span class="w"> </span><span class="bp">∫</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="bp">''</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="bp">∂</span><span class="n">μ</span><span class="w"> </span><span class="bp">=</span><span class="w"> </span><span class="bp">∫</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="k">in</span><span class="w"> </span><span class="n">s</span><span class="o">,</span><span class="w"> </span><span class="bp">|</span><span class="o">(</span><span class="n">f'</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="bp">.</span><span class="n">det</span><span class="bp">|</span><span class="w"> </span><span class="bp">•</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="o">(</span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="o">)</span><span class="w"> </span><span class="bp">∂</span><span class="n">μ</span><span class="w"> </span><span class="o">:=</span> <span class="w"> </span><span class="n">integral_image_eq_integral_abs_det_fderiv_smul</span><span class="w"> </span><span class="n">μ</span><span class="w"> </span><span class="n">hs</span><span class="w"> </span><span class="n">hf</span><span class="w"> </span><span class="n">h_inj</span><span class="w"> </span><span class="n">g</span> <div class="highlight-lean notranslate"><div class="highlight"><pre><span></span><span class="kd">example</span> <span class="o">{</span><span class="n">E</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">NormedAddCommGroup</span> <span class="n">E</span><span class="o">]</span> <span class="o">[</span><span class="n">NormedSpace</span> <span class="n">ℝ</span> <span class="n">E</span><span class="o">]</span> <span class="o">[</span><span class="n">FiniteDimensional</span> <span class="n">ℝ</span> <span class="n">E</span><span class="o">]</span> <span class="o">[</span><span class="n">MeasurableSpace</span> <span class="n">E</span><span class="o">]</span> <span class="o">[</span><span class="n">BorelSpace</span> <span class="n">E</span><span class="o">]</span> <span class="o">(</span><span class="n">μ</span> <span class="o">:</span> <span class="n">Measure</span> <span class="n">E</span><span class="o">)</span> <span class="o">[</span><span class="n">μ.IsAddHaarMeasure</span><span class="o">]</span> <span class="o">{</span><span class="n">F</span> <span class="o">:</span> <span class="kt">Type</span><span class="bp">*</span><span class="o">}</span> <span class="o">[</span><span class="n">NormedAddCommGroup</span> <span class="n">F</span><span class="o">]</span> <span class="o">[</span><span class="n">NormedSpace</span> <span class="n">ℝ</span> <span class="n">F</span><span class="o">]</span> <span class="o">[</span><span class="n">CompleteSpace</span> <span class="n">F</span><span class="o">]</span> <span class="o">{</span><span class="n">s</span> <span class="o">:</span> <span class="n">Set</span> <span class="n">E</span><span class="o">}</span> <span class="o">{</span><span class="n">f</span> <span class="o">:</span> <span class="n">E</span> <span class="bp">→</span> <span class="n">E</span><span class="o">}</span> <span class="o">{</span><span class="n">f'</span> <span class="o">:</span> <span class="n">E</span> <span class="bp">→</span> <span class="n">E</span> <span class="bp">→</span><span class="n">L</span><span class="o">[</span><span class="n">ℝ</span><span class="o">]</span> <span class="n">E</span><span class="o">}</span> <span class="o">(</span><span class="n">hs</span> <span class="o">:</span> <span class="n">MeasurableSet</span> <span class="n">s</span><span class="o">)</span> <span class="o">(</span><span class="n">hf</span> <span class="o">:</span> <span class="bp">∀</span> <span class="n">x</span> <span class="o">:</span> <span class="n">E</span><span class="o">,</span> <span class="n">x</span> <span class="bp">∈</span> <span class="n">s</span> <span class="bp">→</span> <span class="n">HasFDerivWithinAt</span> <span class="n">f</span> <span class="o">(</span><span class="n">f'</span> <span class="n">x</span><span class="o">)</span> <span class="n">s</span> <span class="n">x</span><span class="o">)</span> <span class="o">(</span><span class="n">h_inj</span> <span class="o">:</span> <span class="n">InjOn</span> <span class="n">f</span> <span class="n">s</span><span class="o">)</span> <span class="o">(</span><span class="n">g</span> <span class="o">:</span> <span class="n">E</span> <span class="bp">→</span> <span class="n">F</span><span class="o">)</span> <span class="o">:</span> <span class="bp">∫</span> <span class="n">x</span> <span class="k">in</span> <span class="n">f</span> <span class="bp">''</span> <span class="n">s</span><span class="o">,</span> <span class="n">g</span> <span class="n">x</span> <span class="bp">∂</span><span class="n">μ</span> <span class="bp">=</span> <span class="bp">∫</span> <span class="n">x</span> <span class="k">in</span> <span class="n">s</span><span class="o">,</span> <span class="bp">|</span><span class="o">(</span><span class="n">f'</span> <span class="n">x</span><span class="o">)</span><span class="bp">.</span><span class="n">det</span><span class="bp">|</span> <span class="bp">•</span> <span class="n">g</span> <span class="o">(</span><span class="n">f</span> <span class="n">x</span><span class="o">)</span> <span class="bp">∂</span><span class="n">μ</span> <span class="o">:=</span> <span class="n">integral_image_eq_integral_abs_det_fderiv_smul</span> <span class="n">μ</span> <span class="n">hs</span> <span class="n">hf</span> <span class="n">h_inj</span> <span class="n">g</span> </pre></div> </div> </section>
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@@ -1,15 +1,15 @@/* * doctools.js * ~~~~~~~~~~~ * * Base JavaScript utilities for all Sphinx HTML documentation. * * :copyright: Copyright 2007-2022 by the Sphinx team, see AUTHORS. * :license: BSD, see LICENSE for details. * */ "use strict"; const BLACKLISTED_KEY_CONTROL_ELEMENTS = new Set([ "TEXTAREA", "INPUT", "SELECT", "BUTTON", ]); const _ready = (callback) => { if (document.readyState !== "loading") { callback();
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@@ -18,11 +18,73 @@ const _ready = (callback) => {} }; /** * highlight a given string on a node by wrapping it in * span elements with the given class name. */ const _highlight = (node, addItems, text, className) => { if (node.nodeType === Node.TEXT_NODE) { const val = node.nodeValue; const parent = node.parentNode; const pos = val.toLowerCase().indexOf(text); if ( pos >= 0 && !parent.classList.contains(className) && !parent.classList.contains("nohighlight") ) { let span; const closestNode = parent.closest("body, svg, foreignObject"); const isInSVG = closestNode && closestNode.matches("svg"); if (isInSVG) { span = document.createElementNS("http://www.w3.org/2000/svg", "tspan"); } else { span = document.createElement("span"); span.classList.add(className); } span.appendChild(document.createTextNode(val.substr(pos, text.length))); parent.insertBefore( span, parent.insertBefore( document.createTextNode(val.substr(pos + text.length)), node.nextSibling ) ); node.nodeValue = val.substr(0, pos); if (isInSVG) { const rect = document.createElementNS( "http://www.w3.org/2000/svg", "rect" ); const bbox = parent.getBBox(); rect.x.baseVal.value = bbox.x; rect.y.baseVal.value = bbox.y; rect.width.baseVal.value = bbox.width; rect.height.baseVal.value = bbox.height; rect.setAttribute("class", className); addItems.push({ parent: parent, target: rect }); } } } else if (node.matches && !node.matches("button, select, textarea")) { node.childNodes.forEach((el) => _highlight(el, addItems, text, className)); } }; const _highlightText = (thisNode, text, className) => { let addItems = []; _highlight(thisNode, addItems, text, className); addItems.forEach((obj) => obj.parent.insertAdjacentElement("beforebegin", obj.target) ); }; /** * Small JavaScript module for the documentation. */ const Documentation = { init: () => { Documentation.highlightSearchWords(); Documentation.initDomainIndexTable(); Documentation.initOnKeyListeners(); },
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@@ -64,6 +126,51 @@ const Documentation = {Documentation.LOCALE = catalog.locale; }, /** * highlight the search words provided in the url in the text */ highlightSearchWords: () => { const highlight = new URLSearchParams(window.location.search).get("highlight") || ""; const terms = highlight.toLowerCase().split(/\s+/).filter(x => x); if (terms.length === 0) return; // nothing to do // There should never be more than one element matching "div.body" const divBody = document.querySelectorAll("div.body"); const body = divBody.length ? divBody[0] : document.querySelector("body"); window.setTimeout(() => { terms.forEach((term) => _highlightText(body, term, "highlighted")); }, 10); const searchBox = document.getElementById("searchbox"); if (searchBox === null) return; searchBox.appendChild( document .createRange() .createContextualFragment( '<p class="highlight-link">' + '<a href="javascript:Documentation.hideSearchWords()">' + Documentation.gettext("Hide Search Matches") + "</a></p>" ) ); }, /** * helper function to hide the search marks again */ hideSearchWords: () => { document .querySelectorAll("#searchbox .highlight-link") .forEach((el) => el.remove()); document .querySelectorAll("span.highlighted") .forEach((el) => el.classList.remove("highlighted")); const url = new URL(window.location); url.searchParams.delete("highlight"); window.history.replaceState({}, "", url); }, /** * helper function to focus on search bar */
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@@ -103,11 +210,15 @@ const Documentation = {) return; const blacklistedElements = new Set([ "TEXTAREA", "INPUT", "SELECT", "BUTTON", ]); document.addEventListener("keydown", (event) => { // bail for input elements if (BLACKLISTED_KEY_CONTROL_ELEMENTS.has(document.activeElement.tagName)) return; // bail with special keys if (event.altKey || event.ctrlKey || event.metaKey) return; if (blacklistedElements.has(document.activeElement.tagName)) return; // bail for input elements if (event.altKey || event.ctrlKey || event.metaKey) return; // bail with special keys if (!event.shiftKey) { switch (event.key) {
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@@ -129,6 +240,10 @@ const Documentation = {event.preventDefault(); } break; case "Escape": if (!DOCUMENTATION_OPTIONS.ENABLE_SEARCH_SHORTCUTS) break; Documentation.hideSearchWords(); event.preventDefault(); } }
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@@ -1,4 +1,5 @@const DOCUMENTATION_OPTIONS = { var DOCUMENTATION_OPTIONS = { URL_ROOT: document.getElementById("documentation_options").getAttribute('data-url_root'), VERSION: '0.1', LANGUAGE: 'en', COLLAPSE_INDEX: false,
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@@ -9,5 +10,5 @@ const DOCUMENTATION_OPTIONS = {SOURCELINK_SUFFIX: '.txt', NAVIGATION_WITH_KEYS: false, SHOW_SEARCH_SUMMARY: true, ENABLE_SEARCH_SHORTCUTS: true, ENABLE_SEARCH_SHORTCUTS: false, };
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@@ -0,0 +1,10881 @@/*! * jQuery JavaScript Library v3.6.0 * https://jquery.com/ * * Includes Sizzle.js * https://sizzlejs.com/ * * Copyright OpenJS Foundation and other contributors * Released under the MIT license * https://jquery.org/license * * Date: 2021-03-02T17:08Z */ ( function( global, factory ) { "use strict"; if ( typeof module === "object" && typeof module.exports === "object" ) { // For CommonJS and CommonJS-like environments where a proper `window` // is present, execute the factory and get jQuery. // For environments that do not have a `window` with a `document` // (such as Node.js), expose a factory as module.exports. // This accentuates the need for the creation of a real `window`. // e.g. var jQuery = require("jquery")(window); // See ticket #14549 for more info. module.exports = global.document ? factory( global, true ) : function( w ) { if ( !w.document ) { throw new Error( "jQuery requires a window with a document" ); } return factory( w ); }; } else { factory( global ); } // Pass this if window is not defined yet } )( typeof window !== "undefined" ? window : this, function( window, noGlobal ) { // Edge <= 12 - 13+, Firefox <=18 - 45+, IE 10 - 11, Safari 5.1 - 9+, iOS 6 - 9.1 // throw exceptions when non-strict code (e.g., ASP.NET 4.5) accesses strict mode // arguments.callee.caller (trac-13335). But as of jQuery 3.0 (2016), strict mode should be common // enough that all such attempts are guarded in a try block. "use strict"; var arr = []; var getProto = Object.getPrototypeOf; var slice = arr.slice; var flat = arr.flat ? function( array ) { return arr.flat.call( array ); } : function( array ) { return arr.concat.apply( [], array ); }; var push = arr.push; var indexOf = arr.indexOf; var class2type = {}; var toString = class2type.toString; var hasOwn = class2type.hasOwnProperty; var fnToString = hasOwn.toString; var ObjectFunctionString = fnToString.call( Object ); var support = {}; var isFunction = function isFunction( obj ) { // Support: Chrome <=57, Firefox <=52 // In some browsers, typeof returns "function" for HTML <object> elements // (i.e., `typeof document.createElement( "object" ) === "function"`). // We don't want to classify *any* DOM node as a function. // Support: QtWeb <=3.8.5, WebKit <=534.34, wkhtmltopdf tool <=0.12.5 // Plus for old WebKit, typeof returns "function" for HTML collections // (e.g., `typeof document.getElementsByTagName("div") === "function"`). (gh-4756) return typeof obj === "function" && typeof obj.nodeType !== "number" && typeof obj.item !== "function"; }; var isWindow = function isWindow( obj ) { return obj != null && obj === obj.window; }; var document = window.document; var preservedScriptAttributes = { type: true, src: true, nonce: true, noModule: true }; function DOMEval( code, node, doc ) { doc = doc || document; var i, val, script = doc.createElement( "script" ); script.text = code; if ( node ) { for ( i in preservedScriptAttributes ) { // Support: Firefox 64+, Edge 18+ // Some browsers don't support the "nonce" property on scripts. // On the other hand, just using `getAttribute` is not enough as // the `nonce` attribute is reset to an empty string whenever it // becomes browsing-context connected. // See https://github.com/whatwg/html/issues/2369 // See https://html.spec.whatwg.org/#nonce-attributes // The `node.getAttribute` check was added for the sake of // `jQuery.globalEval` so that it can fake a nonce-containing node // via an object. val = node[ i ] || node.getAttribute && node.getAttribute( i ); if ( val ) { script.setAttribute( i, val ); } } } doc.head.appendChild( script ).parentNode.removeChild( script ); } function toType( obj ) { if ( obj == null ) { return obj + ""; } // Support: Android <=2.3 only (functionish RegExp) return typeof obj === "object" || typeof obj === "function" ? class2type[ toString.call( obj ) ] || "object" : typeof obj; } /* global Symbol */ // Defining this global in .eslintrc.json would create a danger of using the global // unguarded in another place, it seems safer to define global only for this module var version = "3.6.0", // Define a local copy of jQuery jQuery = function( selector, context ) { // The jQuery object is actually just the init constructor 'enhanced' // Need init if jQuery is called (just allow error to be thrown if not included) return new jQuery.fn.init( selector, context ); }; jQuery.fn = jQuery.prototype = { // The current version of jQuery being used jquery: version, constructor: jQuery, // The default length of a jQuery object is 0 length: 0, toArray: function() { return slice.call( this ); }, // Get the Nth element in the matched element set OR // Get the whole matched element set as a clean array get: function( num ) { // Return all the elements in a clean array if ( num == null ) { return slice.call( this ); } // Return just the one element from the set return num < 0 ? this[ num + this.length ] : this[ num ]; }, // Take an array of elements and push it onto the stack // (returning the new matched element set) pushStack: function( elems ) { // Build a new jQuery matched element set var ret = jQuery.merge( this.constructor(), elems ); // Add the old object onto the stack (as a reference) ret.prevObject = this; // Return the newly-formed element set return ret; }, // Execute a callback for every element in the matched set. each: function( callback ) { return jQuery.each( this, callback ); }, map: function( callback ) { return this.pushStack( jQuery.map( this, function( elem, i ) { return callback.call( elem, i, elem ); } ) ); }, slice: function() { return this.pushStack( slice.apply( this, arguments ) ); }, first: function() { return this.eq( 0 ); }, last: function() { return this.eq( -1 ); }, even: function() { return this.pushStack( jQuery.grep( this, function( _elem, i ) { return ( i + 1 ) % 2; } ) ); }, odd: function() { return this.pushStack( jQuery.grep( this, function( _elem, i ) { return i % 2; } ) ); }, eq: function( i ) { var len = this.length, j = +i + ( i < 0 ? len : 0 ); return this.pushStack( j >= 0 && j < len ? [ this[ j ] ] : [] ); }, end: function() { return this.prevObject || this.constructor(); }, // For internal use only. // Behaves like an Array's method, not like a jQuery method. push: push, sort: arr.sort, splice: arr.splice }; jQuery.extend = jQuery.fn.extend = function() { var options, name, src, copy, copyIsArray, clone, target = arguments[ 0 ] || {}, i = 1, length = arguments.length, deep = false; // Handle a deep copy situation if ( typeof target === "boolean" ) { deep = target; // Skip the boolean and the target target = arguments[ i ] || {}; i++; } // Handle case when target is a string or something (possible in deep copy) if ( typeof target !== "object" && !isFunction( target ) ) { target = {}; } // Extend jQuery itself if only one argument is passed if ( i === length ) { target = this; i--; } for ( ; i < length; i++ ) { // Only deal with non-null/undefined values if ( ( options = arguments[ i ] ) != null ) { // Extend the base object for ( name in options ) { copy = options[ name ]; // Prevent Object.prototype pollution // Prevent never-ending loop if ( name === "__proto__" || target === copy ) { continue; } // Recurse if we're merging plain objects or arrays if ( deep && copy && ( jQuery.isPlainObject( copy ) || ( copyIsArray = Array.isArray( copy ) ) ) ) { src = target[ name ]; // Ensure proper type for the source value if ( copyIsArray && !Array.isArray( src ) ) { clone = []; } else if ( !copyIsArray && !jQuery.isPlainObject( src ) ) { clone = {}; } else { clone = src; } copyIsArray = false; // Never move original objects, clone them target[ name ] = jQuery.extend( deep, clone, copy ); // Don't bring in undefined values } else if ( copy !== undefined ) { target[ name ] = copy; } } } } // Return the modified object return target; }; jQuery.extend( { // Unique for each copy of jQuery on the page expando: "jQuery" + ( version + Math.random() ).replace( /\D/g, "" ), // Assume jQuery is ready without the ready module isReady: true, error: function( msg ) { throw new Error( msg ); }, noop: function() {}, isPlainObject: function( obj ) { var proto, Ctor; // Detect obvious negatives // Use toString instead of jQuery.type to catch host objects if ( !obj || toString.call( obj ) !== "[object Object]" ) { return false; } proto = getProto( obj ); // Objects with no prototype (e.g., `Object.create( null )`) are plain if ( !proto ) { return true; } // Objects with prototype are plain iff they were constructed by a global Object function Ctor = hasOwn.call( proto, "constructor" ) && proto.constructor; return typeof Ctor === "function" && fnToString.call( Ctor ) === ObjectFunctionString; }, isEmptyObject: function( obj ) { var name; for ( name in obj ) { return false; } return true; }, // Evaluates a script in a provided context; falls back to the global one // if not specified. globalEval: function( code, options, doc ) { DOMEval( code, { nonce: options && options.nonce }, doc ); }, each: function( obj, callback ) { var length, i = 0; if ( isArrayLike( obj ) ) { length = obj.length; for ( ; i < length; i++ ) { if ( callback.call( obj[ i ], i, obj[ i ] ) === false ) { break; } } } else { for ( i in obj ) { if ( callback.call( obj[ i ], i, obj[ i ] ) === false ) { break; } } } return obj; }, // results is for internal usage only makeArray: function( arr, results ) { var ret = results || []; if ( arr != null ) { if ( isArrayLike( Object( arr ) ) ) { jQuery.merge( ret, typeof arr === "string" ? [ arr ] : arr ); } else { push.call( ret, arr ); } } return ret; }, inArray: function( elem, arr, i ) { return arr == null ? -1 : indexOf.call( arr, elem, i ); }, // Support: Android <=4.0 only, PhantomJS 1 only // push.apply(_, arraylike) throws on ancient WebKit merge: function( first, second ) { var len = +second.length, j = 0, i = first.length; for ( ; j < len; j++ ) { first[ i++ ] = second[ j ]; } first.length = i; return first; }, grep: function( elems, callback, invert ) { var callbackInverse, matches = [], i = 0, length = elems.length, callbackExpect = !invert; // Go through the array, only saving the items // that pass the validator function for ( ; i < length; i++ ) { callbackInverse = !callback( elems[ i ], i ); if ( callbackInverse !== callbackExpect ) { matches.push( elems[ i ] ); } } return matches; }, // arg is for internal usage only map: function( elems, callback, arg ) { var length, value, i = 0, ret = []; // Go through the array, translating each of the items to their new values if ( isArrayLike( elems ) ) { length = elems.length; for ( ; i < length; i++ ) { value = callback( elems[ i ], i, arg ); if ( value != null ) { ret.push( value ); } } // Go through every key on the object, } else { for ( i in elems ) { value = callback( elems[ i ], i, arg ); if ( value != null ) { ret.push( value ); } } } // Flatten any nested arrays return flat( ret ); }, // A global GUID counter for objects guid: 1, // jQuery.support is not used in Core but other projects attach their // properties to it so it needs to exist. support: support } ); if ( typeof Symbol === "function" ) { jQuery.fn[ Symbol.iterator ] = arr[ Symbol.iterator ]; } // Populate the class2type map jQuery.each( "Boolean Number String Function Array Date RegExp Object Error Symbol".split( " " ), function( _i, name ) { class2type[ "[object " + name + "]" ] = name.toLowerCase(); } ); function isArrayLike( obj ) { // Support: real iOS 8.2 only (not reproducible in simulator) // `in` check used to prevent JIT error (gh-2145) // hasOwn isn't used here due to false negatives // regarding Nodelist length in IE var length = !!obj && "length" in obj && obj.length, type = toType( obj ); if ( isFunction( obj ) || isWindow( obj ) ) { return false; } return type === "array" || length === 0 || typeof length === "number" && length > 0 && ( length - 1 ) in obj; } var Sizzle = /*! * Sizzle CSS Selector Engine v2.3.6 * https://sizzlejs.com/ * * Copyright JS Foundation and other contributors * Released under the MIT license * https://js.foundation/ * * Date: 2021-02-16 */ ( function( window ) { var i, support, Expr, getText, isXML, tokenize, compile, select, outermostContext, sortInput, hasDuplicate, // Local document vars setDocument, document, docElem, documentIsHTML, rbuggyQSA, rbuggyMatches, matches, contains, // Instance-specific data expando = "sizzle" + 1 * new Date(), preferredDoc = window.document, dirruns = 0, done = 0, classCache = createCache(), tokenCache = createCache(), compilerCache = createCache(), nonnativeSelectorCache = createCache(), sortOrder = function( a, b ) { if ( a === b ) { hasDuplicate = true; } return 0; }, // Instance methods hasOwn = ( {} ).hasOwnProperty, arr = [], pop = arr.pop, pushNative = arr.push, push = arr.push, slice = arr.slice, // Use a stripped-down indexOf as it's faster than native // https://jsperf.com/thor-indexof-vs-for/5 indexOf = function( list, elem ) { var i = 0, len = list.length; for ( ; i < len; i++ ) { if ( list[ i ] === elem ) { return i; } } return -1; }, booleans = "checked|selected|async|autofocus|autoplay|controls|defer|disabled|hidden|" + "ismap|loop|multiple|open|readonly|required|scoped", // Regular expressions // http://www.w3.org/TR/css3-selectors/#whitespace whitespace = "[\\x20\\t\\r\\n\\f]", // https://www.w3.org/TR/css-syntax-3/#ident-token-diagram identifier = "(?:\\\\[\\da-fA-F]{1,6}" + whitespace + "?|\\\\[^\\r\\n\\f]|[\\w-]|[^\0-\\x7f])+", // Attribute selectors: http://www.w3.org/TR/selectors/#attribute-selectors attributes = "\\[" + whitespace + "*(" + identifier + ")(?:" + whitespace + // Operator (capture 2) "*([*^$|!~]?=)" + whitespace + // "Attribute values must be CSS identifiers [capture 5] // or strings [capture 3 or capture 4]" "*(?:'((?:\\\\.|[^\\\\'])*)'|\"((?:\\\\.|[^\\\\\"])*)\"|(" + identifier + "))|)" + whitespace + "*\\]", pseudos = ":(" + identifier + ")(?:\\((" + // To reduce the number of selectors needing tokenize in the preFilter, prefer arguments: // 1. quoted (capture 3; capture 4 or capture 5) "('((?:\\\\.|[^\\\\'])*)'|\"((?:\\\\.|[^\\\\\"])*)\")|" + // 2. simple (capture 6) "((?:\\\\.|[^\\\\()[\\]]|" + attributes + ")*)|" + // 3. anything else (capture 2) ".*" + ")\\)|)", // Leading and non-escaped trailing whitespace, capturing some non-whitespace characters preceding the latter rwhitespace = new RegExp( whitespace + "+", "g" ), rtrim = new RegExp( "^" + whitespace + "+|((?:^|[^\\\\])(?:\\\\.)*)" + whitespace + "+$", "g" ), rcomma = new RegExp( "^" + whitespace + "*," + whitespace + "*" ), rcombinators = new RegExp( "^" + whitespace + "*([>+~]|" + whitespace + ")" + whitespace + "*" ), rdescend = new RegExp( whitespace + "|>" ), rpseudo = new RegExp( pseudos ), ridentifier = new RegExp( "^" + identifier + "$" ), matchExpr = { "ID": new RegExp( "^#(" + identifier + ")" ), "CLASS": new RegExp( "^\\.(" + identifier + ")" ), "TAG": new RegExp( "^(" + identifier + "|[*])" ), "ATTR": new RegExp( "^" + attributes ), "PSEUDO": new RegExp( "^" + pseudos ), "CHILD": new RegExp( "^:(only|first|last|nth|nth-last)-(child|of-type)(?:\\(" + whitespace + "*(even|odd|(([+-]|)(\\d*)n|)" + whitespace + "*(?:([+-]|)" + whitespace + "*(\\d+)|))" + whitespace + "*\\)|)", "i" ), "bool": new RegExp( "^(?:" + booleans + ")$", "i" ), // For use in libraries implementing .is() // We use this for POS matching in `select` "needsContext": new RegExp( "^" + whitespace + "*[>+~]|:(even|odd|eq|gt|lt|nth|first|last)(?:\\(" + whitespace + "*((?:-\\d)?\\d*)" + whitespace + "*\\)|)(?=[^-]|$)", "i" ) }, rhtml = /HTML$/i, rinputs = /^(?:input|select|textarea|button)$/i, rheader = /^h\d$/i, rnative = /^[^{]+\{\s*\[native \w/, // Easily-parseable/retrievable ID or TAG or CLASS selectors rquickExpr = /^(?:#([\w-]+)|(\w+)|\.([\w-]+))$/, rsibling = /[+~]/, // CSS escapes // http://www.w3.org/TR/CSS21/syndata.html#escaped-characters runescape = new RegExp( "\\\\[\\da-fA-F]{1,6}" + whitespace + "?|\\\\([^\\r\\n\\f])", "g" ), funescape = function( escape, nonHex ) { var high = "0x" + escape.slice( 1 ) - 0x10000; return nonHex ? // Strip the backslash prefix from a non-hex escape sequence nonHex : // Replace a hexadecimal escape sequence with the encoded Unicode code point // Support: IE <=11+ // For values outside the Basic Multilingual Plane (BMP), manually construct a // surrogate pair high < 0 ? String.fromCharCode( high + 0x10000 ) : String.fromCharCode( high >> 10 | 0xD800, high & 0x3FF | 0xDC00 ); }, // CSS string/identifier serialization // https://drafts.csswg.org/cssom/#common-serializing-idioms rcssescape = /([\0-\x1f\x7f]|^-?\d)|^-$|[^\0-\x1f\x7f-\uFFFF\w-]/g, fcssescape = function( ch, asCodePoint ) { if ( asCodePoint ) { // U+0000 NULL becomes U+FFFD REPLACEMENT CHARACTER if ( ch === "\0" ) { return "\uFFFD"; } // Control characters and (dependent upon position) numbers get escaped as code points return ch.slice( 0, -1 ) + "\\" + ch.charCodeAt( ch.length - 1 ).toString( 16 ) + " "; } // Other potentially-special ASCII characters get backslash-escaped return "\\" + ch; }, // Used for iframes // See setDocument() // Removing the function wrapper causes a "Permission Denied" // error in IE unloadHandler = function() { setDocument(); }, inDisabledFieldset = addCombinator( function( elem ) { return elem.disabled === true && elem.nodeName.toLowerCase() === "fieldset"; }, { dir: "parentNode", next: "legend" } ); // Optimize for push.apply( _, NodeList ) try { push.apply( ( arr = slice.call( preferredDoc.childNodes ) ), preferredDoc.childNodes ); // Support: Android<4.0 // Detect silently failing push.apply // eslint-disable-next-line no-unused-expressions arr[ preferredDoc.childNodes.length ].nodeType; } catch ( e ) { push = { apply: arr.length ? // Leverage slice if possible function( target, els ) { pushNative.apply( target, slice.call( els ) ); } : // Support: IE<9 // Otherwise append directly function( target, els ) { var j = target.length, i = 0; // Can't trust NodeList.length while ( ( target[ j++ ] = els[ i++ ] ) ) {} target.length = j - 1; } }; } function Sizzle( selector, context, results, seed ) { var m, i, elem, nid, match, groups, newSelector, newContext = context && context.ownerDocument, // nodeType defaults to 9, since context defaults to document nodeType = context ? context.nodeType : 9; results = results || []; // Return early from calls with invalid selector or context if ( typeof selector !== "string" || !selector || nodeType !== 1 && nodeType !== 9 && nodeType !== 11 ) { return results; } // Try to shortcut find operations (as opposed to filters) in HTML documents if ( !seed ) { setDocument( context ); context = context || document; if ( documentIsHTML ) { // If the selector is sufficiently simple, try using a "get*By*" DOM method // (excepting DocumentFragment context, where the methods don't exist) if ( nodeType !== 11 && ( match = rquickExpr.exec( selector ) ) ) { // ID selector if ( ( m = match[ 1 ] ) ) { // Document context if ( nodeType === 9 ) { if ( ( elem = context.getElementById( m ) ) ) { // Support: IE, Opera, Webkit // TODO: identify versions // getElementById can match elements by name instead of ID if ( elem.id === m ) { results.push( elem ); return results; } } else { return results; } // Element context } else { // Support: IE, Opera, Webkit // TODO: identify versions // getElementById can match elements by name instead of ID if ( newContext && ( elem = newContext.getElementById( m ) ) && contains( context, elem ) && elem.id === m ) { results.push( elem ); return results; } } // Type selector } else if ( match[ 2 ] ) { push.apply( results, context.getElementsByTagName( selector ) ); return results; // Class selector } else if ( ( m = match[ 3 ] ) && support.getElementsByClassName && context.getElementsByClassName ) { push.apply( results, context.getElementsByClassName( m ) ); return results; } } // Take advantage of querySelectorAll if ( support.qsa && !nonnativeSelectorCache[ selector + " " ] && ( !rbuggyQSA || !rbuggyQSA.test( selector ) ) && // Support: IE 8 only // Exclude object elements ( nodeType !== 1 || context.nodeName.toLowerCase() !== "object" ) ) { newSelector = selector; newContext = context; // qSA considers elements outside a scoping root when evaluating child or // descendant combinators, which is not what we want. // In such cases, we work around the behavior by prefixing every selector in the // list with an ID selector referencing the scope context. // The technique has to be used as well when a leading combinator is used // as such selectors are not recognized by querySelectorAll. // Thanks to Andrew Dupont for this technique. if ( nodeType === 1 && ( rdescend.test( selector ) || rcombinators.test( selector ) ) ) { // Expand context for sibling selectors newContext = rsibling.test( selector ) && testContext( context.parentNode ) || context; // We can use :scope instead of the ID hack if the browser // supports it & if we're not changing the context. if ( newContext !== context || !support.scope ) { // Capture the context ID, setting it first if necessary if ( ( nid = context.getAttribute( "id" ) ) ) { nid = nid.replace( rcssescape, fcssescape ); } else { context.setAttribute( "id", ( nid = expando ) ); } } // Prefix every selector in the list groups = tokenize( selector ); i = groups.length; while ( i-- ) { groups[ i ] = ( nid ? "#" + nid : ":scope" ) + " " + toSelector( groups[ i ] ); } newSelector = groups.join( "," ); } try { push.apply( results, newContext.querySelectorAll( newSelector ) ); return results; } catch ( qsaError ) { nonnativeSelectorCache( selector, true ); } finally { if ( nid === expando ) { context.removeAttribute( "id" ); } } } } } // All others return select( selector.replace( rtrim, "$1" ), context, results, seed ); } /** * Create key-value caches of limited size * @returns {function(string, object)} Returns the Object data after storing it on itself with * property name the (space-suffixed) string and (if the cache is larger than Expr.cacheLength) * deleting the oldest entry */ function createCache() { var keys = []; function cache( key, value ) { // Use (key + " ") to avoid collision with native prototype properties (see Issue #157) if ( keys.push( key + " " ) > Expr.cacheLength ) { // Only keep the most recent entries delete cache[ keys.shift() ]; } return ( cache[ key + " " ] = value ); } return cache; } /** * Mark a function for special use by Sizzle * @param {Function} fn The function to mark */ function markFunction( fn ) { fn[ expando ] = true; return fn; } /** * Support testing using an element * @param {Function} fn Passed the created element and returns a boolean result */ function assert( fn ) { var el = document.createElement( "fieldset" ); try { return !!fn( el ); } catch ( e ) { return false; } finally { // Remove from its parent by default if ( el.parentNode ) { el.parentNode.removeChild( el ); } // release memory in IE el = null; } } /** * Adds the same handler for all of the specified attrs * @param {String} attrs Pipe-separated list of attributes * @param {Function} handler The method that will be applied */ function addHandle( attrs, handler ) { var arr = attrs.split( "|" ), i = arr.length; while ( i-- ) { Expr.attrHandle[ arr[ i ] ] = handler; } } /** * Checks document order of two siblings * @param {Element} a * @param {Element} b * @returns {Number} Returns less than 0 if a precedes b, greater than 0 if a follows b */ function siblingCheck( a, b ) { var cur = b && a, diff = cur && a.nodeType === 1 && b.nodeType === 1 && a.sourceIndex - b.sourceIndex; // Use IE sourceIndex if available on both nodes if ( diff ) { return diff; } // Check if b follows a if ( cur ) { while ( ( cur = cur.nextSibling ) ) { if ( cur === b ) { return -1; } } } return a ? 1 : -1; } /** * Returns a function to use in pseudos for input types * @param {String} type */ function createInputPseudo( type ) { return function( elem ) { var name = elem.nodeName.toLowerCase(); return name === "input" && elem.type === type; }; } /** * Returns a function to use in pseudos for buttons * @param {String} type */ function createButtonPseudo( type ) { return function( elem ) { var name = elem.nodeName.toLowerCase(); return ( name === "input" || name === "button" ) && elem.type === type; }; } /** * Returns a function to use in pseudos for :enabled/:disabled * @param {Boolean} disabled true for :disabled; false for :enabled */ function createDisabledPseudo( disabled ) { // Known :disabled false positives: fieldset[disabled] > legend:nth-of-type(n+2) :can-disable return function( elem ) { // Only certain elements can match :enabled or :disabled // https://html.spec.whatwg.org/multipage/scripting.html#selector-enabled // https://html.spec.whatwg.org/multipage/scripting.html#selector-disabled if ( "form" in elem ) { // Check for inherited disabledness on relevant non-disabled elements: // * listed form-associated elements in a disabled fieldset // https://html.spec.whatwg.org/multipage/forms.html#category-listed // https://html.spec.whatwg.org/multipage/forms.html#concept-fe-disabled // * option elements in a disabled optgroup // https://html.spec.whatwg.org/multipage/forms.html#concept-option-disabled // All such elements have a "form" property. if ( elem.parentNode && elem.disabled === false ) { // Option elements defer to a parent optgroup if present if ( "label" in elem ) { if ( "label" in elem.parentNode ) { return elem.parentNode.disabled === disabled; } else { return elem.disabled === disabled; } } // Support: IE 6 - 11 // Use the isDisabled shortcut property to check for disabled fieldset ancestors return elem.isDisabled === disabled || // Where there is no isDisabled, check manually /* jshint -W018 */ elem.isDisabled !== !disabled && inDisabledFieldset( elem ) === disabled; } return elem.disabled === disabled; // Try to winnow out elements that can't be disabled before trusting the disabled property. // Some victims get caught in our net (label, legend, menu, track), but it shouldn't // even exist on them, let alone have a boolean value. } else if ( "label" in elem ) { return elem.disabled === disabled; } // Remaining elements are neither :enabled nor :disabled return false; }; } /** * Returns a function to use in pseudos for positionals * @param {Function} fn */ function createPositionalPseudo( fn ) { return markFunction( function( argument ) { argument = +argument; return markFunction( function( seed, matches ) { var j, matchIndexes = fn( [], seed.length, argument ), i = matchIndexes.length; // Match elements found at the specified indexes while ( i-- ) { if ( seed[ ( j = matchIndexes[ i ] ) ] ) { seed[ j ] = !( matches[ j ] = seed[ j ] ); } } } ); } ); } /** * Checks a node for validity as a Sizzle context * @param {Element|Object=} context * @returns {Element|Object|Boolean} The input node if acceptable, otherwise a falsy value */ function testContext( context ) { return context && typeof context.getElementsByTagName !== "undefined" && context; } // Expose support vars for convenience support = Sizzle.support = {}; /** * Detects XML nodes * @param {Element|Object} elem An element or a document * @returns {Boolean} True iff elem is a non-HTML XML node */ isXML = Sizzle.isXML = function( elem ) { var namespace = elem && elem.namespaceURI, docElem = elem && ( elem.ownerDocument || elem ).documentElement; // Support: IE <=8 // Assume HTML when documentElement doesn't yet exist, such as inside loading iframes // https://bugs.jquery.com/ticket/4833 return !rhtml.test( namespace || docElem && docElem.nodeName || "HTML" ); }; /** * Sets document-related variables once based on the current document * @param {Element|Object} [doc] An element or document object to use to set the document * @returns {Object} Returns the current document */ setDocument = Sizzle.setDocument = function( node ) { var hasCompare, subWindow, doc = node ? node.ownerDocument || node : preferredDoc; // Return early if doc is invalid or already selected // Support: IE 11+, Edge 17 - 18+ // IE/Edge sometimes throw a "Permission denied" error when strict-comparing // two documents; shallow comparisons work. // eslint-disable-next-line eqeqeq if ( doc == document || doc.nodeType !== 9 || !doc.documentElement ) { return document; } // Update global variables document = doc; docElem = document.documentElement; documentIsHTML = !isXML( document ); // Support: IE 9 - 11+, Edge 12 - 18+ // Accessing iframe documents after unload throws "permission denied" errors (jQuery #13936) // Support: IE 11+, Edge 17 - 18+ // IE/Edge sometimes throw a "Permission denied" error when strict-comparing // two documents; shallow comparisons work. // eslint-disable-next-line eqeqeq if ( preferredDoc != document && ( subWindow = document.defaultView ) && subWindow.top !== subWindow ) { // Support: IE 11, Edge if ( subWindow.addEventListener ) { subWindow.addEventListener( "unload", unloadHandler, false ); // Support: IE 9 - 10 only } else if ( subWindow.attachEvent ) { subWindow.attachEvent( "onunload", unloadHandler ); } } // Support: IE 8 - 11+, Edge 12 - 18+, Chrome <=16 - 25 only, Firefox <=3.6 - 31 only, // Safari 4 - 5 only, Opera <=11.6 - 12.x only // IE/Edge & older browsers don't support the :scope pseudo-class. // Support: Safari 6.0 only // Safari 6.0 supports :scope but it's an alias of :root there. support.scope = assert( function( el ) { docElem.appendChild( el ).appendChild( document.createElement( "div" ) ); return typeof el.querySelectorAll !== "undefined" && !el.querySelectorAll( ":scope fieldset div" ).length; } ); /* Attributes ---------------------------------------------------------------------- */ // Support: IE<8 // Verify that getAttribute really returns attributes and not properties // (excepting IE8 booleans) support.attributes = assert( function( el ) { el.className = "i"; return !el.getAttribute( "className" ); } ); /* getElement(s)By* ---------------------------------------------------------------------- */ // Check if getElementsByTagName("*") returns only elements support.getElementsByTagName = assert( function( el ) { el.appendChild( document.createComment( "" ) ); return !el.getElementsByTagName( "*" ).length; } ); // Support: IE<9 support.getElementsByClassName = rnative.test( document.getElementsByClassName ); // Support: IE<10 // Check if getElementById returns elements by name // The broken getElementById methods don't pick up programmatically-set names, // so use a roundabout getElementsByName test support.getById = assert( function( el ) { docElem.appendChild( el ).id = expando; return !document.getElementsByName || !document.getElementsByName( expando ).length; } ); // ID filter and find if ( support.getById ) { Expr.filter[ "ID" ] = function( id ) { var attrId = id.replace( runescape, funescape ); return function( elem ) { return elem.getAttribute( "id" ) === attrId; }; }; Expr.find[ "ID" ] = function( id, context ) { if ( typeof context.getElementById !== "undefined" && documentIsHTML ) { var elem = context.getElementById( id ); return elem ? [ elem ] : []; } }; } else { Expr.filter[ "ID" ] = function( id ) { var attrId = id.replace( runescape, funescape ); return function( elem ) { var node = typeof elem.getAttributeNode !== "undefined" && elem.getAttributeNode( "id" ); return node && node.value === attrId; }; }; // Support: IE 6 - 7 only // getElementById is not reliable as a find shortcut Expr.find[ "ID" ] = function( id, context ) { if ( typeof context.getElementById !== "undefined" && documentIsHTML ) { var node, i, elems, elem = context.getElementById( id ); if ( elem ) { // Verify the id attribute node = elem.getAttributeNode( "id" ); if ( node && node.value === id ) { return [ elem ]; } // Fall back on getElementsByName elems = context.getElementsByName( id ); i = 0; while ( ( elem = elems[ i++ ] ) ) { node = elem.getAttributeNode( "id" ); if ( node && node.value === id ) { return [ elem ]; } } } return []; } }; } // Tag Expr.find[ "TAG" ] = support.getElementsByTagName ? function( tag, context ) { if ( typeof context.getElementsByTagName !== "undefined" ) { return context.getElementsByTagName( tag ); // DocumentFragment nodes don't have gEBTN } else if ( support.qsa ) { return context.querySelectorAll( tag ); } } : function( tag, context ) { var elem, tmp = [], i = 0, // By happy coincidence, a (broken) gEBTN appears on DocumentFragment nodes too results = context.getElementsByTagName( tag ); // Filter out possible comments if ( tag === "*" ) { while ( ( elem = results[ i++ ] ) ) { if ( elem.nodeType === 1 ) { tmp.push( elem ); } } return tmp; } return results; }; // Class Expr.find[ "CLASS" ] = support.getElementsByClassName && function( className, context ) { if ( typeof context.getElementsByClassName !== "undefined" && documentIsHTML ) { return context.getElementsByClassName( className ); } }; /* QSA/matchesSelector ---------------------------------------------------------------------- */ // QSA and matchesSelector support // matchesSelector(:active) reports false when true (IE9/Opera 11.5) rbuggyMatches = []; // qSa(:focus) reports false when true (Chrome 21) // We allow this because of a bug in IE8/9 that throws an error // whenever `document.activeElement` is accessed on an iframe // So, we allow :focus to pass through QSA all the time to avoid the IE error // See https://bugs.jquery.com/ticket/13378 rbuggyQSA = []; if ( ( support.qsa = rnative.test( document.querySelectorAll ) ) ) { // Build QSA regex // Regex strategy adopted from Diego Perini assert( function( el ) { var input; // Select is set to empty string on purpose // This is to test IE's treatment of not explicitly // setting a boolean content attribute, // since its presence should be enough // https://bugs.jquery.com/ticket/12359 docElem.appendChild( el ).innerHTML = "<a id='" + expando + "'></a>" + "<select id='" + expando + "-\r\\' msallowcapture=''>" + "<option selected=''></option></select>"; // Support: IE8, Opera 11-12.16 // Nothing should be selected when empty strings follow ^= or $= or *= // The test attribute must be unknown in Opera but "safe" for WinRT // https://msdn.microsoft.com/en-us/library/ie/hh465388.aspx#attribute_section if ( el.querySelectorAll( "[msallowcapture^='']" ).length ) { rbuggyQSA.push( "[*^$]=" + whitespace + "*(?:''|\"\")" ); } // Support: IE8 // Boolean attributes and "value" are not treated correctly if ( !el.querySelectorAll( "[selected]" ).length ) { rbuggyQSA.push( "\\[" + whitespace + "*(?:value|" + booleans + ")" ); } // Support: Chrome<29, Android<4.4, Safari<7.0+, iOS<7.0+, PhantomJS<1.9.8+ if ( !el.querySelectorAll( "[id~=" + expando + "-]" ).length ) { rbuggyQSA.push( "~=" ); } // Support: IE 11+, Edge 15 - 18+ // IE 11/Edge don't find elements on a `[name='']` query in some cases. // Adding a temporary attribute to the document before the selection works // around the issue. // Interestingly, IE 10 & older don't seem to have the issue. input = document.createElement( "input" ); input.setAttribute( "name", "" ); el.appendChild( input ); if ( !el.querySelectorAll( "[name='']" ).length ) { rbuggyQSA.push( "\\[" + whitespace + "*name" + whitespace + "*=" + whitespace + "*(?:''|\"\")" ); } // Webkit/Opera - :checked should return selected option elements // http://www.w3.org/TR/2011/REC-css3-selectors-20110929/#checked // IE8 throws error here and will not see later tests if ( !el.querySelectorAll( ":checked" ).length ) { rbuggyQSA.push( ":checked" ); } // Support: Safari 8+, iOS 8+ // https://bugs.webkit.org/show_bug.cgi?id=136851 // In-page `selector#id sibling-combinator selector` fails if ( !el.querySelectorAll( "a#" + expando + "+*" ).length ) { rbuggyQSA.push( ".#.+[+~]" ); } // Support: Firefox <=3.6 - 5 only // Old Firefox doesn't throw on a badly-escaped identifier. el.querySelectorAll( "\\\f" ); rbuggyQSA.push( "[\\r\\n\\f]" ); } ); assert( function( el ) { el.innerHTML = "<a href='' disabled='disabled'></a>" + "<select disabled='disabled'><option/></select>"; // Support: Windows 8 Native Apps // The type and name attributes are restricted during .innerHTML assignment var input = document.createElement( "input" ); input.setAttribute( "type", "hidden" ); el.appendChild( input ).setAttribute( "name", "D" ); // Support: IE8 // Enforce case-sensitivity of name attribute if ( el.querySelectorAll( "[name=d]" ).length ) { rbuggyQSA.push( "name" + whitespace + "*[*^$|!~]?=" ); } // FF 3.5 - :enabled/:disabled and hidden elements (hidden elements are still enabled) // IE8 throws error here and will not see later tests if ( el.querySelectorAll( ":enabled" ).length !== 2 ) { rbuggyQSA.push( ":enabled", ":disabled" ); } // Support: IE9-11+ // IE's :disabled selector does not pick up the children of disabled fieldsets docElem.appendChild( el ).disabled = true; if ( el.querySelectorAll( ":disabled" ).length !== 2 ) { rbuggyQSA.push( ":enabled", ":disabled" ); } // Support: Opera 10 - 11 only // Opera 10-11 does not throw on post-comma invalid pseudos el.querySelectorAll( "*,:x" ); rbuggyQSA.push( ",.*:" ); } ); } if ( ( support.matchesSelector = rnative.test( ( matches = docElem.matches || docElem.webkitMatchesSelector || docElem.mozMatchesSelector || docElem.oMatchesSelector || docElem.msMatchesSelector ) ) ) ) { assert( function( el ) { // Check to see if it's possible to do matchesSelector // on a disconnected node (IE 9) support.disconnectedMatch = matches.call( el, "*" ); // This should fail with an exception // Gecko does not error, returns false instead matches.call( el, "[s!='']:x" ); rbuggyMatches.push( "!=", pseudos ); } ); } rbuggyQSA = rbuggyQSA.length && new RegExp( rbuggyQSA.join( "|" ) ); rbuggyMatches = rbuggyMatches.length && new RegExp( rbuggyMatches.join( "|" ) ); /* Contains ---------------------------------------------------------------------- */ hasCompare = rnative.test( docElem.compareDocumentPosition ); // Element contains another // Purposefully self-exclusive // As in, an element does not contain itself contains = hasCompare || rnative.test( docElem.contains ) ? function( a, b ) { var adown = a.nodeType === 9 ? a.documentElement : a, bup = b && b.parentNode; return a === bup || !!( bup && bup.nodeType === 1 && ( adown.contains ? adown.contains( bup ) : a.compareDocumentPosition && a.compareDocumentPosition( bup ) & 16 ) ); } : function( a, b ) { if ( b ) { while ( ( b = b.parentNode ) ) { if ( b === a ) { return true; } } } return false; }; /* Sorting ---------------------------------------------------------------------- */ // Document order sorting sortOrder = hasCompare ? function( a, b ) { // Flag for duplicate removal if ( a === b ) { hasDuplicate = true; return 0; } // Sort on method existence if only one input has compareDocumentPosition var compare = !a.compareDocumentPosition - !b.compareDocumentPosition; if ( compare ) { return compare; } // Calculate position if both inputs belong to the same document // Support: IE 11+, Edge 17 - 18+ // IE/Edge sometimes throw a "Permission denied" error when strict-comparing // two documents; shallow comparisons work. // eslint-disable-next-line eqeqeq compare = ( a.ownerDocument || a ) == ( b.ownerDocument || b ) ? a.compareDocumentPosition( b ) : // Otherwise we know they are disconnected 1; // Disconnected nodes if ( compare & 1 || ( !support.sortDetached && b.compareDocumentPosition( a ) === compare ) ) { // Choose the first element that is related to our preferred document // Support: IE 11+, Edge 17 - 18+ // IE/Edge sometimes throw a "Permission denied" error when strict-comparing // two documents; shallow comparisons work. // eslint-disable-next-line eqeqeq if ( a == document || a.ownerDocument == preferredDoc && contains( preferredDoc, a ) ) { return -1; } // Support: IE 11+, Edge 17 - 18+ // IE/Edge sometimes throw a "Permission denied" error when strict-comparing // two documents; shallow comparisons work. // eslint-disable-next-line eqeqeq if ( b == document || b.ownerDocument == preferredDoc && contains( preferredDoc, b ) ) { return 1; } // Maintain original order return sortInput ? ( indexOf( sortInput, a ) - indexOf( sortInput, b ) ) : 0; } return compare & 4 ? -1 : 1; } : function( a, b ) { // Exit early if the nodes are identical if ( a === b ) { hasDuplicate = true; return 0; } var cur, i = 0, aup = a.parentNode, bup = b.parentNode, ap = [ a ], bp = [ b ]; // Parentless nodes are either documents or disconnected if ( !aup || !bup ) { // Support: IE 11+, Edge 17 - 18+ // IE/Edge sometimes throw a "Permission denied" error when strict-comparing // two documents; shallow comparisons work. /* eslint-disable eqeqeq */ return a == document ? -1 : b == document ? 1 : /* eslint-enable eqeqeq */ aup ? -1 : bup ? 1 : sortInput ? ( indexOf( sortInput, a ) - indexOf( sortInput, b ) ) : 0; // If the nodes are siblings, we can do a quick check } else if ( aup === bup ) { return siblingCheck( a, b ); } // Otherwise we need full lists of their ancestors for comparison cur = a; while ( ( cur = cur.parentNode ) ) { ap.unshift( cur ); } cur = b; while ( ( cur = cur.parentNode ) ) { bp.unshift( cur ); } // Walk down the tree looking for a discrepancy while ( ap[ i ] === bp[ i ] ) { i++; } return i ? // Do a sibling check if the nodes have a common ancestor siblingCheck( ap[ i ], bp[ i ] ) : // Otherwise nodes in our document sort first // Support: IE 11+, Edge 17 - 18+ // IE/Edge sometimes throw a "Permission denied" error when strict-comparing // two documents; shallow comparisons work. /* eslint-disable eqeqeq */ ap[ i ] == preferredDoc ? -1 : bp[ i ] == preferredDoc ? 1 : /* eslint-enable eqeqeq */ 0; }; return document; }; Sizzle.matches = function( expr, elements ) { return Sizzle( expr, null, null, elements ); }; Sizzle.matchesSelector = function( elem, expr ) { setDocument( elem ); if ( support.matchesSelector && documentIsHTML && !nonnativeSelectorCache[ expr + " " ] && ( !rbuggyMatches || !rbuggyMatches.test( expr ) ) && ( !rbuggyQSA || !rbuggyQSA.test( expr ) ) ) { try { var ret = matches.call( elem, expr ); // IE 9's matchesSelector returns false on disconnected nodes if ( ret || support.disconnectedMatch || // As well, disconnected nodes are said to be in a document // fragment in IE 9 elem.document && elem.document.nodeType !== 11 ) { return ret; } } catch ( e ) { nonnativeSelectorCache( expr, true ); } } return Sizzle( expr, document, null, [ elem ] ).length > 0; }; Sizzle.contains = function( context, elem ) { // Set document vars if needed // Support: IE 11+, Edge 17 - 18+ // IE/Edge sometimes throw a "Permission denied" error when strict-comparing // two documents; shallow comparisons work. // eslint-disable-next-line eqeqeq if ( ( context.ownerDocument || context ) != document ) { setDocument( context ); } return contains( context, elem ); }; Sizzle.attr = function( elem, name ) { // Set document vars if needed // Support: IE 11+, Edge 17 - 18+ // IE/Edge sometimes throw a "Permission denied" error when strict-comparing // two documents; shallow comparisons work. // eslint-disable-next-line eqeqeq if ( ( elem.ownerDocument || elem ) != document ) { setDocument( elem ); } var fn = Expr.attrHandle[ name.toLowerCase() ], // Don't get fooled by Object.prototype properties (jQuery #13807) val = fn && hasOwn.call( Expr.attrHandle, name.toLowerCase() ) ? fn( elem, name, !documentIsHTML ) : undefined; return val !== undefined ? val : support.attributes || !documentIsHTML ? elem.getAttribute( name ) : ( val = elem.getAttributeNode( name ) ) && val.specified ? val.value : null; }; Sizzle.escape = function( sel ) { return ( sel + "" ).replace( rcssescape, fcssescape ); }; Sizzle.error = function( msg ) { throw new Error( "Syntax error, unrecognized expression: " + msg ); }; /** * Document sorting and removing duplicates * @param {ArrayLike} results */ Sizzle.uniqueSort = function( results ) { var elem, duplicates = [], j = 0, i = 0; // Unless we *know* we can detect duplicates, assume their presence hasDuplicate = !support.detectDuplicates; sortInput = !support.sortStable && results.slice( 0 ); results.sort( sortOrder ); if ( hasDuplicate ) { while ( ( elem = results[ i++ ] ) ) { if ( elem === results[ i ] ) { j = duplicates.push( i ); } } while ( j-- ) { results.splice( duplicates[ j ], 1 ); } } // Clear input after sorting to release objects // See https://github.com/jquery/sizzle/pull/225 sortInput = null; return results; }; /** * Utility function for retrieving the text value of an array of DOM nodes * @param {Array|Element} elem */ getText = Sizzle.getText = function( elem ) { var node, ret = "", i = 0, nodeType = elem.nodeType; if ( !nodeType ) { // If no nodeType, this is expected to be an array while ( ( node = elem[ i++ ] ) ) { // Do not traverse comment nodes ret += getText( node ); } } else if ( nodeType === 1 || nodeType === 9 || nodeType === 11 ) { // Use textContent for elements // innerText usage removed for consistency of new lines (jQuery #11153) if ( typeof elem.textContent === "string" ) { return elem.textContent; } else { // Traverse its children for ( elem = elem.firstChild; elem; elem = elem.nextSibling ) { ret += getText( elem ); } } } else if ( nodeType === 3 || nodeType === 4 ) { return elem.nodeValue; } // Do not include comment or processing instruction nodes return ret; }; Expr = Sizzle.selectors = { // Can be adjusted by the user cacheLength: 50, createPseudo: markFunction, match: matchExpr, attrHandle: {}, find: {}, relative: { ">": { dir: "parentNode", first: true }, " ": { dir: "parentNode" }, "+": { dir: "previousSibling", first: true }, "~": { dir: "previousSibling" } }, preFilter: { "ATTR": function( match ) { match[ 1 ] = match[ 1 ].replace( runescape, funescape ); // Move the given value to match[3] whether quoted or unquoted match[ 3 ] = ( match[ 3 ] || match[ 4 ] || match[ 5 ] || "" ).replace( runescape, funescape ); if ( match[ 2 ] === "~=" ) { match[ 3 ] = " " + match[ 3 ] + " "; } return match.slice( 0, 4 ); }, "CHILD": function( match ) { /* matches from matchExpr["CHILD"] 1 type (only|nth|...) 2 what (child|of-type) 3 argument (even|odd|\d*|\d*n([+-]\d+)?|...) 4 xn-component of xn+y argument ([+-]?\d*n|) 5 sign of xn-component 6 x of xn-component 7 sign of y-component 8 y of y-component */ match[ 1 ] = match[ 1 ].toLowerCase(); if ( match[ 1 ].slice( 0, 3 ) === "nth" ) { // nth-* requires argument if ( !match[ 3 ] ) { Sizzle.error( match[ 0 ] ); } // numeric x and y parameters for Expr.filter.CHILD // remember that false/true cast respectively to 0/1 match[ 4 ] = +( match[ 4 ] ? match[ 5 ] + ( match[ 6 ] || 1 ) : 2 * ( match[ 3 ] === "even" || match[ 3 ] === "odd" ) ); match[ 5 ] = +( ( match[ 7 ] + match[ 8 ] ) || match[ 3 ] === "odd" ); // other types prohibit arguments } else if ( match[ 3 ] ) { Sizzle.error( match[ 0 ] ); } return match; }, "PSEUDO": function( match ) { var excess, unquoted = !match[ 6 ] && match[ 2 ]; if ( matchExpr[ "CHILD" ].test( match[ 0 ] ) ) { return null; } // Accept quoted arguments as-is if ( match[ 3 ] ) { match[ 2 ] = match[ 4 ] || match[ 5 ] || ""; // Strip excess characters from unquoted arguments } else if ( unquoted && rpseudo.test( unquoted ) && // Get excess from tokenize (recursively) ( excess = tokenize( unquoted, true ) ) && // advance to the next closing parenthesis ( excess = unquoted.indexOf( ")", unquoted.length - excess ) - unquoted.length ) ) { // excess is a negative index match[ 0 ] = match[ 0 ].slice( 0, excess ); match[ 2 ] = unquoted.slice( 0, excess ); } // Return only captures needed by the pseudo filter method (type and argument) return match.slice( 0, 3 ); } }, filter: { "TAG": function( nodeNameSelector ) { var nodeName = nodeNameSelector.replace( runescape, funescape ).toLowerCase(); return nodeNameSelector === "*" ? function() { return true; } : function( elem ) { return elem.nodeName && elem.nodeName.toLowerCase() === nodeName; }; }, "CLASS": function( className ) { var pattern = classCache[ className + " " ]; return pattern || ( pattern = new RegExp( "(^|" + whitespace + ")" + className + "(" + whitespace + "|$)" ) ) && classCache( className, function( elem ) { return pattern.test( typeof elem.className === "string" && elem.className || typeof elem.getAttribute !== "undefined" && elem.getAttribute( "class" ) || "" ); } ); }, "ATTR": function( name, operator, check ) { return function( elem ) { var result = Sizzle.attr( elem, name ); if ( result == null ) { return operator === "!="; } if ( !operator ) { return true; } result += ""; /* eslint-disable max-len */ return operator === "=" ? result === check : operator === "!=" ? result !== check : operator === "^=" ? check && result.indexOf( check ) === 0 : operator === "*=" ? check && result.indexOf( check ) > -1 : operator === "$=" ? check && result.slice( -check.length ) === check : operator === "~=" ? ( " " + result.replace( rwhitespace, " " ) + " " ).indexOf( check ) > -1 : operator === "|=" ? result === check || result.slice( 0, check.length + 1 ) === check + "-" : false; /* eslint-enable max-len */ }; }, "CHILD": function( type, what, _argument, first, last ) { var simple = type.slice( 0, 3 ) !== "nth", forward = type.slice( -4 ) !== "last", ofType = what === "of-type"; return first === 1 && last === 0 ? // Shortcut for :nth-*(n) function( elem ) { return !!elem.parentNode; } : function( elem, _context, xml ) { var cache, uniqueCache, outerCache, node, nodeIndex, start, dir = simple !== forward ? "nextSibling" : "previousSibling", parent = elem.parentNode, name = ofType && elem.nodeName.toLowerCase(), useCache = !xml && !ofType, diff = false; if ( parent ) { // :(first|last|only)-(child|of-type) if ( simple ) { while ( dir ) { node = elem; while ( ( node = node[ dir ] ) ) { if ( ofType ? node.nodeName.toLowerCase() === name : node.nodeType === 1 ) { return false; } } // Reverse direction for :only-* (if we haven't yet done so) start = dir = type === "only" && !start && "nextSibling"; } return true; } start = [ forward ? parent.firstChild : parent.lastChild ]; // non-xml :nth-child(...) stores cache data on `parent` if ( forward && useCache ) { // Seek `elem` from a previously-cached index // ...in a gzip-friendly way node = parent; outerCache = node[ expando ] || ( node[ expando ] = {} ); // Support: IE <9 only // Defend against cloned attroperties (jQuery gh-1709) uniqueCache = outerCache[ node.uniqueID ] || ( outerCache[ node.uniqueID ] = {} ); cache = uniqueCache[ type ] || []; nodeIndex = cache[ 0 ] === dirruns && cache[ 1 ]; diff = nodeIndex && cache[ 2 ]; node = nodeIndex && parent.childNodes[ nodeIndex ]; while ( ( node = ++nodeIndex && node && node[ dir ] || // Fallback to seeking `elem` from the start ( diff = nodeIndex = 0 ) || start.pop() ) ) { // When found, cache indexes on `parent` and break if ( node.nodeType === 1 && ++diff && node === elem ) { uniqueCache[ type ] = [ dirruns, nodeIndex, diff ]; break; } } } else { // Use previously-cached element index if available if ( useCache ) { // ...in a gzip-friendly way node = elem; outerCache = node[ expando ] || ( node[ expando ] = {} ); // Support: IE <9 only // Defend against cloned attroperties (jQuery gh-1709) uniqueCache = outerCache[ node.uniqueID ] || ( outerCache[ node.uniqueID ] = {} ); cache = uniqueCache[ type ] || []; nodeIndex = cache[ 0 ] === dirruns && cache[ 1 ]; diff = nodeIndex; } // xml :nth-child(...) // or :nth-last-child(...) or :nth(-last)?-of-type(...) if ( diff === false ) { // Use the same loop as above to seek `elem` from the start while ( ( node = ++nodeIndex && node && node[ dir ] || ( diff = nodeIndex = 0 ) || start.pop() ) ) { if ( ( ofType ? node.nodeName.toLowerCase() === name : node.nodeType === 1 ) && ++diff ) { // Cache the index of each encountered element if ( useCache ) { outerCache = node[ expando ] || ( node[ expando ] = {} ); // Support: IE <9 only // Defend against cloned attroperties (jQuery gh-1709) uniqueCache = outerCache[ node.uniqueID ] || ( outerCache[ node.uniqueID ] = {} ); uniqueCache[ type ] = [ dirruns, diff ]; } if ( node === elem ) { break; } } } } } // Incorporate the offset, then check against cycle size diff -= last; return diff === first || ( diff % first === 0 && diff / first >= 0 ); } }; }, "PSEUDO": function( pseudo, argument ) { // pseudo-class names are case-insensitive // http://www.w3.org/TR/selectors/#pseudo-classes // Prioritize by case sensitivity in case custom pseudos are added with uppercase letters // Remember that setFilters inherits from pseudos var args, fn = Expr.pseudos[ pseudo ] || Expr.setFilters[ pseudo.toLowerCase() ] || Sizzle.error( "unsupported pseudo: " + pseudo ); // The user may use createPseudo to indicate that // arguments are needed to create the filter function // just as Sizzle does if ( fn[ expando ] ) { return fn( argument ); } // But maintain support for old signatures if ( fn.length > 1 ) { args = [ pseudo, pseudo, "", argument ]; return Expr.setFilters.hasOwnProperty( pseudo.toLowerCase() ) ? markFunction( function( seed, matches ) { var idx, matched = fn( seed, argument ), i = matched.length; while ( i-- ) { idx = indexOf( seed, matched[ i ] ); seed[ idx ] = !( matches[ idx ] = matched[ i ] ); } } ) : function( elem ) { return fn( elem, 0, args ); }; } return fn; } }, pseudos: { // Potentially complex pseudos "not": markFunction( function( selector ) { // Trim the selector passed to compile // to avoid treating leading and trailing // spaces as combinators var input = [], results = [], matcher = compile( selector.replace( rtrim, "$1" ) ); return matcher[ expando ] ? markFunction( function( seed, matches, _context, xml ) { var elem, unmatched = matcher( seed, null, xml, [] ), i = seed.length; // Match elements unmatched by `matcher` while ( i-- ) { if ( ( elem = unmatched[ i ] ) ) { seed[ i ] = !( matches[ i ] = elem ); } } } ) : function( elem, _context, xml ) { input[ 0 ] = elem; matcher( input, null, xml, results ); // Don't keep the element (issue #299) input[ 0 ] = null; return !results.pop(); }; } ), "has": markFunction( function( selector ) { return function( elem ) { return Sizzle( selector, elem ).length > 0; }; } ), "contains": markFunction( function( text ) { text = text.replace( runescape, funescape ); return function( elem ) { return ( elem.textContent || getText( elem ) ).indexOf( text ) > -1; }; } ), // "Whether an element is represented by a :lang() selector // is based solely on the element's language value // being equal to the identifier C, // or beginning with the identifier C immediately followed by "-". // The matching of C against the element's language value is performed case-insensitively. // The identifier C does not have to be a valid language name." // http://www.w3.org/TR/selectors/#lang-pseudo "lang": markFunction( function( lang ) { // lang value must be a valid identifier if ( !ridentifier.test( lang || "" ) ) { Sizzle.error( "unsupported lang: " + lang ); } lang = lang.replace( runescape, funescape ).toLowerCase(); return function( elem ) { var elemLang; do { if ( ( elemLang = documentIsHTML ? elem.lang : elem.getAttribute( "xml:lang" ) || elem.getAttribute( "lang" ) ) ) { elemLang = elemLang.toLowerCase(); return elemLang === lang || elemLang.indexOf( lang + "-" ) === 0; } } while ( ( elem = elem.parentNode ) && elem.nodeType === 1 ); return false; }; } ), // Miscellaneous "target": function( elem ) { var hash = window.location && window.location.hash; return hash && hash.slice( 1 ) === elem.id; }, "root": function( elem ) { return elem === docElem; }, "focus": function( elem ) { return elem === document.activeElement && ( !document.hasFocus || document.hasFocus() ) && !!( elem.type || elem.href || ~elem.tabIndex ); }, // Boolean properties "enabled": createDisabledPseudo( false ), "disabled": createDisabledPseudo( true ), "checked": function( elem ) { // In CSS3, :checked should return both checked and selected elements // http://www.w3.org/TR/2011/REC-css3-selectors-20110929/#checked var nodeName = elem.nodeName.toLowerCase(); return ( nodeName === "input" && !!elem.checked ) || ( nodeName === "option" && !!elem.selected ); }, "selected": function( elem ) { // Accessing this property makes selected-by-default // options in Safari work properly if ( elem.parentNode ) { // eslint-disable-next-line no-unused-expressions elem.parentNode.selectedIndex; } return elem.selected === true; }, // Contents "empty": function( elem ) { // http://www.w3.org/TR/selectors/#empty-pseudo // :empty is negated by element (1) or content nodes (text: 3; cdata: 4; entity ref: 5), // but not by others (comment: 8; processing instruction: 7; etc.) // nodeType < 6 works because attributes (2) do not appear as children for ( elem = elem.firstChild; elem; elem = elem.nextSibling ) { if ( elem.nodeType < 6 ) { return false; } } return true; }, "parent": function( elem ) { return !Expr.pseudos[ "empty" ]( elem ); }, // Element/input types "header": function( elem ) { return rheader.test( elem.nodeName ); }, "input": function( elem ) { return rinputs.test( elem.nodeName ); }, "button": function( elem ) { var name = elem.nodeName.toLowerCase(); return name === "input" && elem.type === "button" || name === "button"; }, "text": function( elem ) { var attr; return elem.nodeName.toLowerCase() === "input" && elem.type === "text" && // Support: IE<8 // New HTML5 attribute values (e.g., "search") appear with elem.type === "text" ( ( attr = elem.getAttribute( "type" ) ) == null || attr.toLowerCase() === "text" ); }, // Position-in-collection "first": createPositionalPseudo( function() { return [ 0 ]; } ), "last": createPositionalPseudo( function( _matchIndexes, length ) { return [ length - 1 ]; } ), "eq": createPositionalPseudo( function( _matchIndexes, length, argument ) { return [ argument < 0 ? argument + length : argument ]; } ), "even": createPositionalPseudo( function( matchIndexes, length ) { var i = 0; for ( ; i < length; i += 2 ) { matchIndexes.push( i ); } return matchIndexes; } ), "odd": createPositionalPseudo( function( matchIndexes, length ) { var i = 1; for ( ; i < length; i += 2 ) { matchIndexes.push( i ); } return matchIndexes; } ), "lt": createPositionalPseudo( function( matchIndexes, length, argument ) { var i = argument < 0 ? argument + length : argument > length ? length : argument; for ( ; --i >= 0; ) { matchIndexes.push( i ); } return matchIndexes; } ), "gt": createPositionalPseudo( function( matchIndexes, length, argument ) { var i = argument < 0 ? argument + length : argument; for ( ; ++i < length; ) { matchIndexes.push( i ); } return matchIndexes; } ) } }; Expr.pseudos[ "nth" ] = Expr.pseudos[ "eq" ]; // Add button/input type pseudos for ( i in { radio: true, checkbox: true, file: true, password: true, image: true } ) { Expr.pseudos[ i ] = createInputPseudo( i ); } for ( i in { submit: true, reset: true } ) { Expr.pseudos[ i ] = createButtonPseudo( i ); } // Easy API for creating new setFilters function setFilters() {} setFilters.prototype = Expr.filters = Expr.pseudos; Expr.setFilters = new setFilters(); tokenize = Sizzle.tokenize = function( selector, parseOnly ) { var matched, match, tokens, type, soFar, groups, preFilters, cached = tokenCache[ selector + " " ]; if ( cached ) { return parseOnly ? 0 : cached.slice( 0 ); } soFar = selector; groups = []; preFilters = Expr.preFilter; while ( soFar ) { // Comma and first run if ( !matched || ( match = rcomma.exec( soFar ) ) ) { if ( match ) { // Don't consume trailing commas as valid soFar = soFar.slice( match[ 0 ].length ) || soFar; } groups.push( ( tokens = [] ) ); } matched = false; // Combinators if ( ( match = rcombinators.exec( soFar ) ) ) { matched = match.shift(); tokens.push( { value: matched, // Cast descendant combinators to space type: match[ 0 ].replace( rtrim, " " ) } ); soFar = soFar.slice( matched.length ); } // Filters for ( type in Expr.filter ) { if ( ( match = matchExpr[ type ].exec( soFar ) ) && ( !preFilters[ type ] || ( match = preFilters[ type ]( match ) ) ) ) { matched = match.shift(); tokens.push( { value: matched, type: type, matches: match } ); soFar = soFar.slice( matched.length ); } } if ( !matched ) { break; } } // Return the length of the invalid excess // if we're just parsing // Otherwise, throw an error or return tokens return parseOnly ? soFar.length : soFar ? Sizzle.error( selector ) : // Cache the tokens tokenCache( selector, groups ).slice( 0 ); }; function toSelector( tokens ) { var i = 0, len = tokens.length, selector = ""; for ( ; i < len; i++ ) { selector += tokens[ i ].value; } return selector; } function addCombinator( matcher, combinator, base ) { var dir = combinator.dir, skip = combinator.next, key = skip || dir, checkNonElements = base && key === "parentNode", doneName = done++; return combinator.first ? // Check against closest ancestor/preceding element function( elem, context, xml ) { while ( ( elem = elem[ dir ] ) ) { if ( elem.nodeType === 1 || checkNonElements ) { return matcher( elem, context, xml ); } } return false; } : // Check against all ancestor/preceding elements function( elem, context, xml ) { var oldCache, uniqueCache, outerCache, newCache = [ dirruns, doneName ]; // We can't set arbitrary data on XML nodes, so they don't benefit from combinator caching if ( xml ) { while ( ( elem = elem[ dir ] ) ) { if ( elem.nodeType === 1 || checkNonElements ) { if ( matcher( elem, context, xml ) ) { return true; } } } } else { while ( ( elem = elem[ dir ] ) ) { if ( elem.nodeType === 1 || checkNonElements ) { outerCache = elem[ expando ] || ( elem[ expando ] = {} ); // Support: IE <9 only // Defend against cloned attroperties (jQuery gh-1709) uniqueCache = outerCache[ elem.uniqueID ] || ( outerCache[ elem.uniqueID ] = {} ); if ( skip && skip === elem.nodeName.toLowerCase() ) { elem = elem[ dir ] || elem; } else if ( ( oldCache = uniqueCache[ key ] ) && oldCache[ 0 ] === dirruns && oldCache[ 1 ] === doneName ) { // Assign to newCache so results back-propagate to previous elements return ( newCache[ 2 ] = oldCache[ 2 ] ); } else { // Reuse newcache so results back-propagate to previous elements uniqueCache[ key ] = newCache; // A match means we're done; a fail means we have to keep checking if ( ( newCache[ 2 ] = matcher( elem, context, xml ) ) ) { return true; } } } } } return false; }; } function elementMatcher( matchers ) { return matchers.length > 1 ? function( elem, context, xml ) { var i = matchers.length; while ( i-- ) { if ( !matchers[ i ]( elem, context, xml ) ) { return false; } } return true; } : matchers[ 0 ]; } function multipleContexts( selector, contexts, results ) { var i = 0, len = contexts.length; for ( ; i < len; i++ ) { Sizzle( selector, contexts[ i ], results ); } return results; } function condense( unmatched, map, filter, context, xml ) { var elem, newUnmatched = [], i = 0, len = unmatched.length, mapped = map != null; for ( ; i < len; i++ ) { if ( ( elem = unmatched[ i ] ) ) { if ( !filter || filter( elem, context, xml ) ) { newUnmatched.push( elem ); if ( mapped ) { map.push( i ); } } } } return newUnmatched; } function setMatcher( preFilter, selector, matcher, postFilter, postFinder, postSelector ) { if ( postFilter && !postFilter[ expando ] ) { postFilter = setMatcher( postFilter ); } if ( postFinder && !postFinder[ expando ] ) { postFinder = setMatcher( postFinder, postSelector ); } return markFunction( function( seed, results, context, xml ) { var temp, i, elem, preMap = [], postMap = [], preexisting = results.length, // Get initial elements from seed or context elems = seed || multipleContexts( selector || "*", context.nodeType ? [ context ] : context, [] ), // Prefilter to get matcher input, preserving a map for seed-results synchronization matcherIn = preFilter && ( seed || !selector ) ? condense( elems, preMap, preFilter, context, xml ) : elems, matcherOut = matcher ? // If we have a postFinder, or filtered seed, or non-seed postFilter or preexisting results, postFinder || ( seed ? preFilter : preexisting || postFilter ) ? // ...intermediate processing is necessary [] : // ...otherwise use results directly results : matcherIn; // Find primary matches if ( matcher ) { matcher( matcherIn, matcherOut, context, xml ); } // Apply postFilter if ( postFilter ) { temp = condense( matcherOut, postMap ); postFilter( temp, [], context, xml ); // Un-match failing elements by moving them back to matcherIn i = temp.length; while ( i-- ) { if ( ( elem = temp[ i ] ) ) { matcherOut[ postMap[ i ] ] = !( matcherIn[ postMap[ i ] ] = elem ); } } } if ( seed ) { if ( postFinder || preFilter ) { if ( postFinder ) { // Get the final matcherOut by condensing this intermediate into postFinder contexts temp = []; i = matcherOut.length; while ( i-- ) { if ( ( elem = matcherOut[ i ] ) ) { // Restore matcherIn since elem is not yet a final match temp.push( ( matcherIn[ i ] = elem ) ); } } postFinder( null, ( matcherOut = [] ), temp, xml ); } // Move matched elements from seed to results to keep them synchronized i = matcherOut.length; while ( i-- ) { if ( ( elem = matcherOut[ i ] ) && ( temp = postFinder ? indexOf( seed, elem ) : preMap[ i ] ) > -1 ) { seed[ temp ] = !( results[ temp ] = elem ); } } } // Add elements to results, through postFinder if defined } else { matcherOut = condense( matcherOut === results ? matcherOut.splice( preexisting, matcherOut.length ) : matcherOut ); if ( postFinder ) { postFinder( null, results, matcherOut, xml ); } else { push.apply( results, matcherOut ); } } } ); } function matcherFromTokens( tokens ) { var checkContext, matcher, j, len = tokens.length, leadingRelative = Expr.relative[ tokens[ 0 ].type ], implicitRelative = leadingRelative || Expr.relative[ " " ], i = leadingRelative ? 1 : 0, // The foundational matcher ensures that elements are reachable from top-level context(s) matchContext = addCombinator( function( elem ) { return elem === checkContext; }, implicitRelative, true ), matchAnyContext = addCombinator( function( elem ) { return indexOf( checkContext, elem ) > -1; }, implicitRelative, true ), matchers = [ function( elem, context, xml ) { var ret = ( !leadingRelative && ( xml || context !== outermostContext ) ) || ( ( checkContext = context ).nodeType ? matchContext( elem, context, xml ) : matchAnyContext( elem, context, xml ) ); // Avoid hanging onto element (issue #299) checkContext = null; return ret; } ]; for ( ; i < len; i++ ) { if ( ( matcher = Expr.relative[ tokens[ i ].type ] ) ) { matchers = [ addCombinator( elementMatcher( matchers ), matcher ) ]; } else { matcher = Expr.filter[ tokens[ i ].type ].apply( null, tokens[ i ].matches ); // Return special upon seeing a positional matcher if ( matcher[ expando ] ) { // Find the next relative operator (if any) for proper handling j = ++i; for ( ; j < len; j++ ) { if ( Expr.relative[ tokens[ j ].type ] ) { break; } } return setMatcher( i > 1 && elementMatcher( matchers ), i > 1 && toSelector( // If the preceding token was a descendant combinator, insert an implicit any-element `*` tokens .slice( 0, i - 1 ) .concat( { value: tokens[ i - 2 ].type === " " ? "*" : "" } ) ).replace( rtrim, "$1" ), matcher, i < j && matcherFromTokens( tokens.slice( i, j ) ), j < len && matcherFromTokens( ( tokens = tokens.slice( j ) ) ), j < len && toSelector( tokens ) ); } matchers.push( matcher ); } } return elementMatcher( matchers ); } function matcherFromGroupMatchers( elementMatchers, setMatchers ) { var bySet = setMatchers.length > 0, byElement = elementMatchers.length > 0, superMatcher = function( seed, context, xml, results, outermost ) { var elem, j, matcher, matchedCount = 0, i = "0", unmatched = seed && [], setMatched = [], contextBackup = outermostContext, // We must always have either seed elements or outermost context elems = seed || byElement && Expr.find[ "TAG" ]( "*", outermost ), // Use integer dirruns iff this is the outermost matcher dirrunsUnique = ( dirruns += contextBackup == null ? 1 : Math.random() || 0.1 ), len = elems.length; if ( outermost ) { // Support: IE 11+, Edge 17 - 18+ // IE/Edge sometimes throw a "Permission denied" error when strict-comparing // two documents; shallow comparisons work. // eslint-disable-next-line eqeqeq outermostContext = context == document || context || outermost; } // Add elements passing elementMatchers directly to results // Support: IE<9, Safari // Tolerate NodeList properties (IE: "length"; Safari: <number>) matching elements by id for ( ; i !== len && ( elem = elems[ i ] ) != null; i++ ) { if ( byElement && elem ) { j = 0; // Support: IE 11+, Edge 17 - 18+ // IE/Edge sometimes throw a "Permission denied" error when strict-comparing // two documents; shallow comparisons work. // eslint-disable-next-line eqeqeq if ( !context && elem.ownerDocument != document ) { setDocument( elem ); xml = !documentIsHTML; } while ( ( matcher = elementMatchers[ j++ ] ) ) { if ( matcher( elem, context || document, xml ) ) { results.push( elem ); break; } } if ( outermost ) { dirruns = dirrunsUnique; } } // Track unmatched elements for set filters if ( bySet ) { // They will have gone through all possible matchers if ( ( elem = !matcher && elem ) ) { matchedCount--; } // Lengthen the array for every element, matched or not if ( seed ) { unmatched.push( elem ); } } } // `i` is now the count of elements visited above, and adding it to `matchedCount` // makes the latter nonnegative. matchedCount += i; // Apply set filters to unmatched elements // NOTE: This can be skipped if there are no unmatched elements (i.e., `matchedCount` // equals `i`), unless we didn't visit _any_ elements in the above loop because we have // no element matchers and no seed. // Incrementing an initially-string "0" `i` allows `i` to remain a string only in that // case, which will result in a "00" `matchedCount` that differs from `i` but is also // numerically zero. if ( bySet && i !== matchedCount ) { j = 0; while ( ( matcher = setMatchers[ j++ ] ) ) { matcher( unmatched, setMatched, context, xml ); } if ( seed ) { // Reintegrate element matches to eliminate the need for sorting if ( matchedCount > 0 ) { while ( i-- ) { if ( !( unmatched[ i ] || setMatched[ i ] ) ) { setMatched[ i ] = pop.call( results ); } } } // Discard index placeholder values to get only actual matches setMatched = condense( setMatched ); } // Add matches to results push.apply( results, setMatched ); // Seedless set matches succeeding multiple successful matchers stipulate sorting if ( outermost && !seed && setMatched.length > 0 && ( matchedCount + setMatchers.length ) > 1 ) { Sizzle.uniqueSort( results ); } } // Override manipulation of globals by nested matchers if ( outermost ) { dirruns = dirrunsUnique; outermostContext = contextBackup; } return unmatched; }; return bySet ? markFunction( superMatcher ) : superMatcher; } compile = Sizzle.compile = function( selector, match /* Internal Use Only */ ) { var i, setMatchers = [], elementMatchers = [], cached = compilerCache[ selector + " " ]; if ( !cached ) { // Generate a function of recursive functions that can be used to check each element if ( !match ) { match = tokenize( selector ); } i = match.length; while ( i-- ) { cached = matcherFromTokens( match[ i ] ); if ( cached[ expando ] ) { setMatchers.push( cached ); } else { elementMatchers.push( cached ); } } // Cache the compiled function cached = compilerCache( selector, matcherFromGroupMatchers( elementMatchers, setMatchers ) ); // Save selector and tokenization cached.selector = selector; } return cached; }; /** * A low-level selection function that works with Sizzle's compiled * selector functions * @param {String|Function} selector A selector or a pre-compiled * selector function built with Sizzle.compile * @param {Element} context * @param {Array} [results] * @param {Array} [seed] A set of elements to match against */ select = Sizzle.select = function( selector, context, results, seed ) { var i, tokens, token, type, find, compiled = typeof selector === "function" && selector, match = !seed && tokenize( ( selector = compiled.selector || selector ) ); results = results || []; // Try to minimize operations if there is only one selector in the list and no seed // (the latter of which guarantees us context) if ( match.length === 1 ) { // Reduce context if the leading compound selector is an ID tokens = match[ 0 ] = match[ 0 ].slice( 0 ); if ( tokens.length > 2 && ( token = tokens[ 0 ] ).type === "ID" && context.nodeType === 9 && documentIsHTML && Expr.relative[ tokens[ 1 ].type ] ) { context = ( Expr.find[ "ID" ]( token.matches[ 0 ] .replace( runescape, funescape ), context ) || [] )[ 0 ]; if ( !context ) { return results; // Precompiled matchers will still verify ancestry, so step up a level } else if ( compiled ) { context = context.parentNode; } selector = selector.slice( tokens.shift().value.length ); } // Fetch a seed set for right-to-left matching i = matchExpr[ "needsContext" ].test( selector ) ? 0 : tokens.length; while ( i-- ) { token = tokens[ i ]; // Abort if we hit a combinator if ( Expr.relative[ ( type = token.type ) ] ) { break; } if ( ( find = Expr.find[ type ] ) ) { // Search, expanding context for leading sibling combinators if ( ( seed = find( token.matches[ 0 ].replace( runescape, funescape ), rsibling.test( tokens[ 0 ].type ) && testContext( context.parentNode ) || context ) ) ) { // If seed is empty or no tokens remain, we can return early tokens.splice( i, 1 ); selector = seed.length && toSelector( tokens ); if ( !selector ) { push.apply( results, seed ); return results; } break; } } } } // Compile and execute a filtering function if one is not provided // Provide `match` to avoid retokenization if we modified the selector above ( compiled || compile( selector, match ) )( seed, context, !documentIsHTML, results, !context || rsibling.test( selector ) && testContext( context.parentNode ) || context ); return results; }; // One-time assignments // Sort stability support.sortStable = expando.split( "" ).sort( sortOrder ).join( "" ) === expando; // Support: Chrome 14-35+ // Always assume duplicates if they aren't passed to the comparison function support.detectDuplicates = !!hasDuplicate; // Initialize against the default document setDocument(); // Support: Webkit<537.32 - Safari 6.0.3/Chrome 25 (fixed in Chrome 27) // Detached nodes confoundingly follow *each other* support.sortDetached = assert( function( el ) { // Should return 1, but returns 4 (following) return el.compareDocumentPosition( document.createElement( "fieldset" ) ) & 1; } ); // Support: IE<8 // Prevent attribute/property "interpolation" // https://msdn.microsoft.com/en-us/library/ms536429%28VS.85%29.aspx if ( !assert( function( el ) { el.innerHTML = "<a href='#'></a>"; return el.firstChild.getAttribute( "href" ) === "#"; } ) ) { addHandle( "type|href|height|width", function( elem, name, isXML ) { if ( !isXML ) { return elem.getAttribute( name, name.toLowerCase() === "type" ? 1 : 2 ); } } ); } // Support: IE<9 // Use defaultValue in place of getAttribute("value") if ( !support.attributes || !assert( function( el ) { el.innerHTML = "<input/>"; el.firstChild.setAttribute( "value", "" ); return el.firstChild.getAttribute( "value" ) === ""; } ) ) { addHandle( "value", function( elem, _name, isXML ) { if ( !isXML && elem.nodeName.toLowerCase() === "input" ) { return elem.defaultValue; } } ); } // Support: IE<9 // Use getAttributeNode to fetch booleans when getAttribute lies if ( !assert( function( el ) { return el.getAttribute( "disabled" ) == null; } ) ) { addHandle( booleans, function( elem, name, isXML ) { var val; if ( !isXML ) { return elem[ name ] === true ? name.toLowerCase() : ( val = elem.getAttributeNode( name ) ) && val.specified ? val.value : null; } } ); } return Sizzle; } )( window ); jQuery.find = Sizzle; jQuery.expr = Sizzle.selectors; // Deprecated jQuery.expr[ ":" ] = jQuery.expr.pseudos; jQuery.uniqueSort = jQuery.unique = Sizzle.uniqueSort; jQuery.text = Sizzle.getText; jQuery.isXMLDoc = Sizzle.isXML; jQuery.contains = Sizzle.contains; jQuery.escapeSelector = Sizzle.escape; var dir = function( elem, dir, until ) { var matched = [], truncate = until !== undefined; while ( ( elem = elem[ dir ] ) && elem.nodeType !== 9 ) { if ( elem.nodeType === 1 ) { if ( truncate && jQuery( elem ).is( until ) ) { break; } matched.push( elem ); } } return matched; }; var siblings = function( n, elem ) { var matched = []; for ( ; n; n = n.nextSibling ) { if ( n.nodeType === 1 && n !== elem ) { matched.push( n ); } } return matched; }; var rneedsContext = jQuery.expr.match.needsContext; function nodeName( elem, name ) { return elem.nodeName && elem.nodeName.toLowerCase() === name.toLowerCase(); } var rsingleTag = ( /^<([a-z][^\/\0>:\x20\t\r\n\f]*)[\x20\t\r\n\f]*\/?>(?:<\/\1>|)$/i ); // Implement the identical functionality for filter and not function winnow( elements, qualifier, not ) { if ( isFunction( qualifier ) ) { return jQuery.grep( elements, function( elem, i ) { return !!qualifier.call( elem, i, elem ) !== not; } ); } // Single element if ( qualifier.nodeType ) { return jQuery.grep( elements, function( elem ) { return ( elem === qualifier ) !== not; } ); } // Arraylike of elements (jQuery, arguments, Array) if ( typeof qualifier !== "string" ) { return jQuery.grep( elements, function( elem ) { return ( indexOf.call( qualifier, elem ) > -1 ) !== not; } ); } // Filtered directly for both simple and complex selectors return jQuery.filter( qualifier, elements, not ); } jQuery.filter = function( expr, elems, not ) { var elem = elems[ 0 ]; if ( not ) { expr = ":not(" + expr + ")"; } if ( elems.length === 1 && elem.nodeType === 1 ) { return jQuery.find.matchesSelector( elem, expr ) ? [ elem ] : []; } return jQuery.find.matches( expr, jQuery.grep( elems, function( elem ) { return elem.nodeType === 1; } ) ); }; jQuery.fn.extend( { find: function( selector ) { var i, ret, len = this.length, self = this; if ( typeof selector !== "string" ) { return this.pushStack( jQuery( selector ).filter( function() { for ( i = 0; i < len; i++ ) { if ( jQuery.contains( self[ i ], this ) ) { return true; } } } ) ); } ret = this.pushStack( [] ); for ( i = 0; i < len; i++ ) { jQuery.find( selector, self[ i ], ret ); } return len > 1 ? jQuery.uniqueSort( ret ) : ret; }, filter: function( selector ) { return this.pushStack( winnow( this, selector || [], false ) ); }, not: function( selector ) { return this.pushStack( winnow( this, selector || [], true ) ); }, is: function( selector ) { return !!winnow( this, // If this is a positional/relative selector, check membership in the returned set // so $("p:first").is("p:last") won't return true for a doc with two "p". typeof selector === "string" && rneedsContext.test( selector ) ? jQuery( selector ) : selector || [], false ).length; } } ); // Initialize a jQuery object // A central reference to the root jQuery(document) var rootjQuery, // A simple way to check for HTML strings // Prioritize #id over <tag> to avoid XSS via location.hash (#9521) // Strict HTML recognition (#11290: must start with <) // Shortcut simple #id case for speed rquickExpr = /^(?:\s*(<[\w\W]+>)[^>]*|#([\w-]+))$/, init = jQuery.fn.init = function( selector, context, root ) { var match, elem; // HANDLE: $(""), $(null), $(undefined), $(false) if ( !selector ) { return this; } // Method init() accepts an alternate rootjQuery // so migrate can support jQuery.sub (gh-2101) root = root || rootjQuery; // Handle HTML strings if ( typeof selector === "string" ) { if ( selector[ 0 ] === "<" && selector[ selector.length - 1 ] === ">" && selector.length >= 3 ) { // Assume that strings that start and end with <> are HTML and skip the regex check match = [ null, selector, null ]; } else { match = rquickExpr.exec( selector ); } // Match html or make sure no context is specified for #id if ( match && ( match[ 1 ] || !context ) ) { // HANDLE: $(html) -> $(array) if ( match[ 1 ] ) { context = context instanceof jQuery ? context[ 0 ] : context; // Option to run scripts is true for back-compat // Intentionally let the error be thrown if parseHTML is not present jQuery.merge( this, jQuery.parseHTML( match[ 1 ], context && context.nodeType ? context.ownerDocument || context : document, true ) ); // HANDLE: $(html, props) if ( rsingleTag.test( match[ 1 ] ) && jQuery.isPlainObject( context ) ) { for ( match in context ) { // Properties of context are called as methods if possible if ( isFunction( this[ match ] ) ) { this[ match ]( context[ match ] ); // ...and otherwise set as attributes } else { this.attr( match, context[ match ] ); } } } return this; // HANDLE: $(#id) } else { elem = document.getElementById( match[ 2 ] ); if ( elem ) { // Inject the element directly into the jQuery object this[ 0 ] = elem; this.length = 1; } return this; } // HANDLE: $(expr, $(...)) } else if ( !context || context.jquery ) { return ( context || root ).find( selector ); // HANDLE: $(expr, context) // (which is just equivalent to: $(context).find(expr) } else { return this.constructor( context ).find( selector ); } // HANDLE: $(DOMElement) } else if ( selector.nodeType ) { this[ 0 ] = selector; this.length = 1; return this; // HANDLE: $(function) // Shortcut for document ready } else if ( isFunction( selector ) ) { return root.ready !== undefined ? root.ready( selector ) : // Execute immediately if ready is not present selector( jQuery ); } return jQuery.makeArray( selector, this ); }; // Give the init function the jQuery prototype for later instantiation init.prototype = jQuery.fn; // Initialize central reference rootjQuery = jQuery( document ); var rparentsprev = /^(?:parents|prev(?:Until|All))/, // Methods guaranteed to produce a unique set when starting from a unique set guaranteedUnique = { children: true, contents: true, next: true, prev: true }; jQuery.fn.extend( { has: function( target ) { var targets = jQuery( target, this ), l = targets.length; return this.filter( function() { var i = 0; for ( ; i < l; i++ ) { if ( jQuery.contains( this, targets[ i ] ) ) { return true; } } } ); }, closest: function( selectors, context ) { var cur, i = 0, l = this.length, matched = [], targets = typeof selectors !== "string" && jQuery( selectors ); // Positional selectors never match, since there's no _selection_ context if ( !rneedsContext.test( selectors ) ) { for ( ; i < l; i++ ) { for ( cur = this[ i ]; cur && cur !== context; cur = cur.parentNode ) { // Always skip document fragments if ( cur.nodeType < 11 && ( targets ? targets.index( cur ) > -1 : // Don't pass non-elements to Sizzle cur.nodeType === 1 && jQuery.find.matchesSelector( cur, selectors ) ) ) { matched.push( cur ); break; } } } } return this.pushStack( matched.length > 1 ? jQuery.uniqueSort( matched ) : matched ); }, // Determine the position of an element within the set index: function( elem ) { // No argument, return index in parent if ( !elem ) { return ( this[ 0 ] && this[ 0 ].parentNode ) ? this.first().prevAll().length : -1; } // Index in selector if ( typeof elem === "string" ) { return indexOf.call( jQuery( elem ), this[ 0 ] ); } // Locate the position of the desired element return indexOf.call( this, // If it receives a jQuery object, the first element is used elem.jquery ? elem[ 0 ] : elem ); }, add: function( selector, context ) { return this.pushStack( jQuery.uniqueSort( jQuery.merge( this.get(), jQuery( selector, context ) ) ) ); }, addBack: function( selector ) { return this.add( selector == null ? this.prevObject : this.prevObject.filter( selector ) ); } } ); function sibling( cur, dir ) { while ( ( cur = cur[ dir ] ) && cur.nodeType !== 1 ) {} return cur; } jQuery.each( { parent: function( elem ) { var parent = elem.parentNode; return parent && parent.nodeType !== 11 ? parent : null; }, parents: function( elem ) { return dir( elem, "parentNode" ); }, parentsUntil: function( elem, _i, until ) { return dir( elem, "parentNode", until ); }, next: function( elem ) { return sibling( elem, "nextSibling" ); }, prev: function( elem ) { return sibling( elem, "previousSibling" ); }, nextAll: function( elem ) { return dir( elem, "nextSibling" ); }, prevAll: function( elem ) { return dir( elem, "previousSibling" ); }, nextUntil: function( elem, _i, until ) { return dir( elem, "nextSibling", until ); }, prevUntil: function( elem, _i, until ) { return dir( elem, "previousSibling", until ); }, siblings: function( elem ) { return siblings( ( elem.parentNode || {} ).firstChild, elem ); }, children: function( elem ) { return siblings( elem.firstChild ); }, contents: function( elem ) { if ( elem.contentDocument != null && // Support: IE 11+ // <object> elements with no `data` attribute has an object // `contentDocument` with a `null` prototype. getProto( elem.contentDocument ) ) { return elem.contentDocument; } // Support: IE 9 - 11 only, iOS 7 only, Android Browser <=4.3 only // Treat the template element as a regular one in browsers that // don't support it. if ( nodeName( elem, "template" ) ) { elem = elem.content || elem; } return jQuery.merge( [], elem.childNodes ); } }, function( name, fn ) { jQuery.fn[ name ] = function( until, selector ) { var matched = jQuery.map( this, fn, until ); if ( name.slice( -5 ) !== "Until" ) { selector = until; } if ( selector && typeof selector === "string" ) { matched = jQuery.filter( selector, matched ); } if ( this.length > 1 ) { // Remove duplicates if ( !guaranteedUnique[ name ] ) { jQuery.uniqueSort( matched ); } // Reverse order for parents* and prev-derivatives if ( rparentsprev.test( name ) ) { matched.reverse(); } } return this.pushStack( matched ); }; } ); var rnothtmlwhite = ( /[^\x20\t\r\n\f]+/g ); // Convert String-formatted options into Object-formatted ones function createOptions( options ) { var object = {}; jQuery.each( options.match( rnothtmlwhite ) || [], function( _, flag ) { object[ flag ] = true; } ); return object; } /* * Create a callback list using the following parameters: * * options: an optional list of space-separated options that will change how * the callback list behaves or a more traditional option object * * By default a callback list will act like an event callback list and can be * "fired" multiple times. * * Possible options: * * once: will ensure the callback list can only be fired once (like a Deferred) * * memory: will keep track of previous values and will call any callback added * after the list has been fired right away with the latest "memorized" * values (like a Deferred) * * unique: will ensure a callback can only be added once (no duplicate in the list) * * stopOnFalse: interrupt callings when a callback returns false * */ jQuery.Callbacks = function( options ) { // Convert options from String-formatted to Object-formatted if needed // (we check in cache first) options = typeof options === "string" ? createOptions( options ) : jQuery.extend( {}, options ); var // Flag to know if list is currently firing firing, // Last fire value for non-forgettable lists memory, // Flag to know if list was already fired fired, // Flag to prevent firing locked, // Actual callback list list = [], // Queue of execution data for repeatable lists queue = [], // Index of currently firing callback (modified by add/remove as needed) firingIndex = -1, // Fire callbacks fire = function() { // Enforce single-firing locked = locked || options.once; // Execute callbacks for all pending executions, // respecting firingIndex overrides and runtime changes fired = firing = true; for ( ; queue.length; firingIndex = -1 ) { memory = queue.shift(); while ( ++firingIndex < list.length ) { // Run callback and check for early termination if ( list[ firingIndex ].apply( memory[ 0 ], memory[ 1 ] ) === false && options.stopOnFalse ) { // Jump to end and forget the data so .add doesn't re-fire firingIndex = list.length; memory = false; } } } // Forget the data if we're done with it if ( !options.memory ) { memory = false; } firing = false; // Clean up if we're done firing for good if ( locked ) { // Keep an empty list if we have data for future add calls if ( memory ) { list = []; // Otherwise, this object is spent } else { list = ""; } } }, // Actual Callbacks object self = { // Add a callback or a collection of callbacks to the list add: function() { if ( list ) { // If we have memory from a past run, we should fire after adding if ( memory && !firing ) { firingIndex = list.length - 1; queue.push( memory ); } ( function add( args ) { jQuery.each( args, function( _, arg ) { if ( isFunction( arg ) ) { if ( !options.unique || !self.has( arg ) ) { list.push( arg ); } } else if ( arg && arg.length && toType( arg ) !== "string" ) { // Inspect recursively add( arg ); } } ); } )( arguments ); if ( memory && !firing ) { fire(); } } return this; }, // Remove a callback from the list remove: function() { jQuery.each( arguments, function( _, arg ) { var index; while ( ( index = jQuery.inArray( arg, list, index ) ) > -1 ) { list.splice( index, 1 ); // Handle firing indexes if ( index <= firingIndex ) { firingIndex--; } } } ); return this; }, // Check if a given callback is in the list. // If no argument is given, return whether or not list has callbacks attached. has: function( fn ) { return fn ? jQuery.inArray( fn, list ) > -1 : list.length > 0; }, // Remove all callbacks from the list empty: function() { if ( list ) { list = []; } return this; }, // Disable .fire and .add // Abort any current/pending executions // Clear all callbacks and values disable: function() { locked = queue = []; list = memory = ""; return this; }, disabled: function() { return !list; }, // Disable .fire // Also disable .add unless we have memory (since it would have no effect) // Abort any pending executions lock: function() { locked = queue = []; if ( !memory && !firing ) { list = memory = ""; } return this; }, locked: function() { return !!locked; }, // Call all callbacks with the given context and arguments fireWith: function( context, args ) { if ( !locked ) { args = args || []; args = [ context, args.slice ? args.slice() : args ]; queue.push( args ); if ( !firing ) { fire(); } } return this; }, // Call all the callbacks with the given arguments fire: function() { self.fireWith( this, arguments ); return this; }, // To know if the callbacks have already been called at least once fired: function() { return !!fired; } }; return self; }; function Identity( v ) { return v; } function Thrower( ex ) { throw ex; } function adoptValue( value, resolve, reject, noValue ) { var method; try { // Check for promise aspect first to privilege synchronous behavior if ( value && isFunction( ( method = value.promise ) ) ) { method.call( value ).done( resolve ).fail( reject ); // Other thenables } else if ( value && isFunction( ( method = value.then ) ) ) { method.call( value, resolve, reject ); // Other non-thenables } else { // Control `resolve` arguments by letting Array#slice cast boolean `noValue` to integer: // * false: [ value ].slice( 0 ) => resolve( value ) // * true: [ value ].slice( 1 ) => resolve() resolve.apply( undefined, [ value ].slice( noValue ) ); } // For Promises/A+, convert exceptions into rejections // Since jQuery.when doesn't unwrap thenables, we can skip the extra checks appearing in // Deferred#then to conditionally suppress rejection. } catch ( value ) { // Support: Android 4.0 only // Strict mode functions invoked without .call/.apply get global-object context reject.apply( undefined, [ value ] ); } } jQuery.extend( { Deferred: function( func ) { var tuples = [ // action, add listener, callbacks, // ... .then handlers, argument index, [final state] [ "notify", "progress", jQuery.Callbacks( "memory" ), jQuery.Callbacks( "memory" ), 2 ], [ "resolve", "done", jQuery.Callbacks( "once memory" ), jQuery.Callbacks( "once memory" ), 0, "resolved" ], [ "reject", "fail", jQuery.Callbacks( "once memory" ), jQuery.Callbacks( "once memory" ), 1, "rejected" ] ], state = "pending", promise = { state: function() { return state; }, always: function() { deferred.done( arguments ).fail( arguments ); return this; }, "catch": function( fn ) { return promise.then( null, fn ); }, // Keep pipe for back-compat pipe: function( /* fnDone, fnFail, fnProgress */ ) { var fns = arguments; return jQuery.Deferred( function( newDefer ) { jQuery.each( tuples, function( _i, tuple ) { // Map tuples (progress, done, fail) to arguments (done, fail, progress) var fn = isFunction( fns[ tuple[ 4 ] ] ) && fns[ tuple[ 4 ] ]; // deferred.progress(function() { bind to newDefer or newDefer.notify }) // deferred.done(function() { bind to newDefer or newDefer.resolve }) // deferred.fail(function() { bind to newDefer or newDefer.reject }) deferred[ tuple[ 1 ] ]( function() { var returned = fn && fn.apply( this, arguments ); if ( returned && isFunction( returned.promise ) ) { returned.promise() .progress( newDefer.notify ) .done( newDefer.resolve ) .fail( newDefer.reject ); } else { newDefer[ tuple[ 0 ] + "With" ]( this, fn ? [ returned ] : arguments ); } } ); } ); fns = null; } ).promise(); }, then: function( onFulfilled, onRejected, onProgress ) { var maxDepth = 0; function resolve( depth, deferred, handler, special ) { return function() { var that = this, args = arguments, mightThrow = function() { var returned, then; // Support: Promises/A+ section 2.3.3.3.3 // https://promisesaplus.com/#point-59 // Ignore double-resolution attempts if ( depth < maxDepth ) { return; } returned = handler.apply( that, args ); // Support: Promises/A+ section 2.3.1 // https://promisesaplus.com/#point-48 if ( returned === deferred.promise() ) { throw new TypeError( "Thenable self-resolution" ); } // Support: Promises/A+ sections 2.3.3.1, 3.5 // https://promisesaplus.com/#point-54 // https://promisesaplus.com/#point-75 // Retrieve `then` only once then = returned && // Support: Promises/A+ section 2.3.4 // https://promisesaplus.com/#point-64 // Only check objects and functions for thenability ( typeof returned === "object" || typeof returned === "function" ) && returned.then; // Handle a returned thenable if ( isFunction( then ) ) { // Special processors (notify) just wait for resolution if ( special ) { then.call( returned, resolve( maxDepth, deferred, Identity, special ), resolve( maxDepth, deferred, Thrower, special ) ); // Normal processors (resolve) also hook into progress } else { // ...and disregard older resolution values maxDepth++; then.call( returned, resolve( maxDepth, deferred, Identity, special ), resolve( maxDepth, deferred, Thrower, special ), resolve( maxDepth, deferred, Identity, deferred.notifyWith ) ); } // Handle all other returned values } else { // Only substitute handlers pass on context // and multiple values (non-spec behavior) if ( handler !== Identity ) { that = undefined; args = [ returned ]; } // Process the value(s) // Default process is resolve ( special || deferred.resolveWith )( that, args ); } }, // Only normal processors (resolve) catch and reject exceptions process = special ? mightThrow : function() { try { mightThrow(); } catch ( e ) { if ( jQuery.Deferred.exceptionHook ) { jQuery.Deferred.exceptionHook( e, process.stackTrace ); } // Support: Promises/A+ section 2.3.3.3.4.1 // https://promisesaplus.com/#point-61 // Ignore post-resolution exceptions if ( depth + 1 >= maxDepth ) { // Only substitute handlers pass on context // and multiple values (non-spec behavior) if ( handler !== Thrower ) { that = undefined; args = [ e ]; } deferred.rejectWith( that, args ); } } }; // Support: Promises/A+ section 2.3.3.3.1 // https://promisesaplus.com/#point-57 // Re-resolve promises immediately to dodge false rejection from // subsequent errors if ( depth ) { process(); } else { // Call an optional hook to record the stack, in case of exception // since it's otherwise lost when execution goes async if ( jQuery.Deferred.getStackHook ) { process.stackTrace = jQuery.Deferred.getStackHook(); } window.setTimeout( process ); } }; } return jQuery.Deferred( function( newDefer ) { // progress_handlers.add( ... ) tuples[ 0 ][ 3 ].add( resolve( 0, newDefer, isFunction( onProgress ) ? onProgress : Identity, newDefer.notifyWith ) ); // fulfilled_handlers.add( ... ) tuples[ 1 ][ 3 ].add( resolve( 0, newDefer, isFunction( onFulfilled ) ? onFulfilled : Identity ) ); // rejected_handlers.add( ... ) tuples[ 2 ][ 3 ].add( resolve( 0, newDefer, isFunction( onRejected ) ? onRejected : Thrower ) ); } ).promise(); }, // Get a promise for this deferred // If obj is provided, the promise aspect is added to the object promise: function( obj ) { return obj != null ? jQuery.extend( obj, promise ) : promise; } }, deferred = {}; // Add list-specific methods jQuery.each( tuples, function( i, tuple ) { var list = tuple[ 2 ], stateString = tuple[ 5 ]; // promise.progress = list.add // promise.done = list.add // promise.fail = list.add promise[ tuple[ 1 ] ] = list.add; // Handle state if ( stateString ) { list.add( function() { // state = "resolved" (i.e., fulfilled) // state = "rejected" state = stateString; }, // rejected_callbacks.disable // fulfilled_callbacks.disable tuples[ 3 - i ][ 2 ].disable, // rejected_handlers.disable // fulfilled_handlers.disable tuples[ 3 - i ][ 3 ].disable, // progress_callbacks.lock tuples[ 0 ][ 2 ].lock, // progress_handlers.lock tuples[ 0 ][ 3 ].lock ); } // progress_handlers.fire // fulfilled_handlers.fire // rejected_handlers.fire list.add( tuple[ 3 ].fire ); // deferred.notify = function() { deferred.notifyWith(...) } // deferred.resolve = function() { deferred.resolveWith(...) } // deferred.reject = function() { deferred.rejectWith(...) } deferred[ tuple[ 0 ] ] = function() { deferred[ tuple[ 0 ] + "With" ]( this === deferred ? undefined : this, arguments ); return this; }; // deferred.notifyWith = list.fireWith // deferred.resolveWith = list.fireWith // deferred.rejectWith = list.fireWith deferred[ tuple[ 0 ] + "With" ] = list.fireWith; } ); // Make the deferred a promise promise.promise( deferred ); // Call given func if any if ( func ) { func.call( deferred, deferred ); } // All done! return deferred; }, // Deferred helper when: function( singleValue ) { var // count of uncompleted subordinates remaining = arguments.length, // count of unprocessed arguments i = remaining, // subordinate fulfillment data resolveContexts = Array( i ), resolveValues = slice.call( arguments ), // the primary Deferred primary = jQuery.Deferred(), // subordinate callback factory updateFunc = function( i ) { return function( value ) { resolveContexts[ i ] = this; resolveValues[ i ] = arguments.length > 1 ? slice.call( arguments ) : value; if ( !( --remaining ) ) { primary.resolveWith( resolveContexts, resolveValues ); } }; }; // Single- and empty arguments are adopted like Promise.resolve if ( remaining <= 1 ) { adoptValue( singleValue, primary.done( updateFunc( i ) ).resolve, primary.reject, !remaining ); // Use .then() to unwrap secondary thenables (cf. gh-3000) if ( primary.state() === "pending" || isFunction( resolveValues[ i ] && resolveValues[ i ].then ) ) { return primary.then(); } } // Multiple arguments are aggregated like Promise.all array elements while ( i-- ) { adoptValue( resolveValues[ i ], updateFunc( i ), primary.reject ); } return primary.promise(); } } ); // These usually indicate a programmer mistake during development, // warn about them ASAP rather than swallowing them by default. var rerrorNames = /^(Eval|Internal|Range|Reference|Syntax|Type|URI)Error$/; jQuery.Deferred.exceptionHook = function( error, stack ) { // Support: IE 8 - 9 only // Console exists when dev tools are open, which can happen at any time if ( window.console && window.console.warn && error && rerrorNames.test( error.name ) ) { window.console.warn( "jQuery.Deferred exception: " + error.message, error.stack, stack ); } }; jQuery.readyException = function( error ) { window.setTimeout( function() { throw error; } ); }; // The deferred used on DOM ready var readyList = jQuery.Deferred(); jQuery.fn.ready = function( fn ) { readyList .then( fn ) // Wrap jQuery.readyException in a function so that the lookup // happens at the time of error handling instead of callback // registration. .catch( function( error ) { jQuery.readyException( error ); } ); return this; }; jQuery.extend( { // Is the DOM ready to be used? Set to true once it occurs. isReady: false, // A counter to track how many items to wait for before // the ready event fires. See #6781 readyWait: 1, // Handle when the DOM is ready ready: function( wait ) { // Abort if there are pending holds or we're already ready if ( wait === true ? --jQuery.readyWait : jQuery.isReady ) { return; } // Remember that the DOM is ready jQuery.isReady = true; // If a normal DOM Ready event fired, decrement, and wait if need be if ( wait !== true && --jQuery.readyWait > 0 ) { return; } // If there are functions bound, to execute readyList.resolveWith( document, [ jQuery ] ); } } ); jQuery.ready.then = readyList.then; // The ready event handler and self cleanup method function completed() { document.removeEventListener( "DOMContentLoaded", completed ); window.removeEventListener( "load", completed ); jQuery.ready(); } // Catch cases where $(document).ready() is called // after the browser event has already occurred. // Support: IE <=9 - 10 only // Older IE sometimes signals "interactive" too soon if ( document.readyState === "complete" || ( document.readyState !== "loading" && !document.documentElement.doScroll ) ) { // Handle it asynchronously to allow scripts the opportunity to delay ready window.setTimeout( jQuery.ready ); } else { // Use the handy event callback document.addEventListener( "DOMContentLoaded", completed ); // A fallback to window.onload, that will always work window.addEventListener( "load", completed ); } // Multifunctional method to get and set values of a collection // The value/s can optionally be executed if it's a function var access = function( elems, fn, key, value, chainable, emptyGet, raw ) { var i = 0, len = elems.length, bulk = key == null; // Sets many values if ( toType( key ) === "object" ) { chainable = true; for ( i in key ) { access( elems, fn, i, key[ i ], true, emptyGet, raw ); } // Sets one value } else if ( value !== undefined ) { chainable = true; if ( !isFunction( value ) ) { raw = true; } if ( bulk ) { // Bulk operations run against the entire set if ( raw ) { fn.call( elems, value ); fn = null; // ...except when executing function values } else { bulk = fn; fn = function( elem, _key, value ) { return bulk.call( jQuery( elem ), value ); }; } } if ( fn ) { for ( ; i < len; i++ ) { fn( elems[ i ], key, raw ? value : value.call( elems[ i ], i, fn( elems[ i ], key ) ) ); } } } if ( chainable ) { return elems; } // Gets if ( bulk ) { return fn.call( elems ); } return len ? fn( elems[ 0 ], key ) : emptyGet; }; // Matches dashed string for camelizing var rmsPrefix = /^-ms-/, rdashAlpha = /-([a-z])/g; // Used by camelCase as callback to replace() function fcamelCase( _all, letter ) { return letter.toUpperCase(); } // Convert dashed to camelCase; used by the css and data modules // Support: IE <=9 - 11, Edge 12 - 15 // Microsoft forgot to hump their vendor prefix (#9572) function camelCase( string ) { return string.replace( rmsPrefix, "ms-" ).replace( rdashAlpha, fcamelCase ); } var acceptData = function( owner ) { // Accepts only: // - Node // - Node.ELEMENT_NODE // - Node.DOCUMENT_NODE // - Object // - Any return owner.nodeType === 1 || owner.nodeType === 9 || !( +owner.nodeType ); }; function Data() { this.expando = jQuery.expando + Data.uid++; } Data.uid = 1; Data.prototype = { cache: function( owner ) { // Check if the owner object already has a cache var value = owner[ this.expando ]; // If not, create one if ( !value ) { value = {}; // We can accept data for non-element nodes in modern browsers, // but we should not, see #8335. // Always return an empty object. if ( acceptData( owner ) ) { // If it is a node unlikely to be stringify-ed or looped over // use plain assignment if ( owner.nodeType ) { owner[ this.expando ] = value; // Otherwise secure it in a non-enumerable property // configurable must be true to allow the property to be // deleted when data is removed } else { Object.defineProperty( owner, this.expando, { value: value, configurable: true } ); } } } return value; }, set: function( owner, data, value ) { var prop, cache = this.cache( owner ); // Handle: [ owner, key, value ] args // Always use camelCase key (gh-2257) if ( typeof data === "string" ) { cache[ camelCase( data ) ] = value; // Handle: [ owner, { properties } ] args } else { // Copy the properties one-by-one to the cache object for ( prop in data ) { cache[ camelCase( prop ) ] = data[ prop ]; } } return cache; }, get: function( owner, key ) { return key === undefined ? this.cache( owner ) : // Always use camelCase key (gh-2257) owner[ this.expando ] && owner[ this.expando ][ camelCase( key ) ]; }, access: function( owner, key, value ) { // In cases where either: // // 1. No key was specified // 2. A string key was specified, but no value provided // // Take the "read" path and allow the get method to determine // which value to return, respectively either: // // 1. The entire cache object // 2. The data stored at the key // if ( key === undefined || ( ( key && typeof key === "string" ) && value === undefined ) ) { return this.get( owner, key ); } // When the key is not a string, or both a key and value // are specified, set or extend (existing objects) with either: // // 1. An object of properties // 2. A key and value // this.set( owner, key, value ); // Since the "set" path can have two possible entry points // return the expected data based on which path was taken[*] return value !== undefined ? value : key; }, remove: function( owner, key ) { var i, cache = owner[ this.expando ]; if ( cache === undefined ) { return; } if ( key !== undefined ) { // Support array or space separated string of keys if ( Array.isArray( key ) ) { // If key is an array of keys... // We always set camelCase keys, so remove that. key = key.map( camelCase ); } else { key = camelCase( key ); // If a key with the spaces exists, use it. // Otherwise, create an array by matching non-whitespace key = key in cache ? [ key ] : ( key.match( rnothtmlwhite ) || [] ); } i = key.length; while ( i-- ) { delete cache[ key[ i ] ]; } } // Remove the expando if there's no more data if ( key === undefined || jQuery.isEmptyObject( cache ) ) { // Support: Chrome <=35 - 45 // Webkit & Blink performance suffers when deleting properties // from DOM nodes, so set to undefined instead // https://bugs.chromium.org/p/chromium/issues/detail?id=378607 (bug restricted) if ( owner.nodeType ) { owner[ this.expando ] = undefined; } else { delete owner[ this.expando ]; } } }, hasData: function( owner ) { var cache = owner[ this.expando ]; return cache !== undefined && !jQuery.isEmptyObject( cache ); } }; var dataPriv = new Data(); var dataUser = new Data(); // Implementation Summary // // 1. Enforce API surface and semantic compatibility with 1.9.x branch // 2. Improve the module's maintainability by reducing the storage // paths to a single mechanism. // 3. Use the same single mechanism to support "private" and "user" data. // 4. _Never_ expose "private" data to user code (TODO: Drop _data, _removeData) // 5. Avoid exposing implementation details on user objects (eg. expando properties) // 6. Provide a clear path for implementation upgrade to WeakMap in 2014 var rbrace = /^(?:\{[\w\W]*\}|\[[\w\W]*\])$/, rmultiDash = /[A-Z]/g; function getData( data ) { if ( data === "true" ) { return true; } if ( data === "false" ) { return false; } if ( data === "null" ) { return null; } // Only convert to a number if it doesn't change the string if ( data === +data + "" ) { return +data; } if ( rbrace.test( data ) ) { return JSON.parse( data ); } return data; } function dataAttr( elem, key, data ) { var name; // If nothing was found internally, try to fetch any // data from the HTML5 data-* attribute if ( data === undefined && elem.nodeType === 1 ) { name = "data-" + key.replace( rmultiDash, "-$&" ).toLowerCase(); data = elem.getAttribute( name ); if ( typeof data === "string" ) { try { data = getData( data ); } catch ( e ) {} // Make sure we set the data so it isn't changed later dataUser.set( elem, key, data ); } else { data = undefined; } } return data; } jQuery.extend( { hasData: function( elem ) { return dataUser.hasData( elem ) || dataPriv.hasData( elem ); }, data: function( elem, name, data ) { return dataUser.access( elem, name, data ); }, removeData: function( elem, name ) { dataUser.remove( elem, name ); }, // TODO: Now that all calls to _data and _removeData have been replaced // with direct calls to dataPriv methods, these can be deprecated. _data: function( elem, name, data ) { return dataPriv.access( elem, name, data ); }, _removeData: function( elem, name ) { dataPriv.remove( elem, name ); } } ); jQuery.fn.extend( { data: function( key, value ) { var i, name, data, elem = this[ 0 ], attrs = elem && elem.attributes; // Gets all values if ( key === undefined ) { if ( this.length ) { data = dataUser.get( elem ); if ( elem.nodeType === 1 && !dataPriv.get( elem, "hasDataAttrs" ) ) { i = attrs.length; while ( i-- ) { // Support: IE 11 only // The attrs elements can be null (#14894) if ( attrs[ i ] ) { name = attrs[ i ].name; if ( name.indexOf( "data-" ) === 0 ) { name = camelCase( name.slice( 5 ) ); dataAttr( elem, name, data[ name ] ); } } } dataPriv.set( elem, "hasDataAttrs", true ); } } return data; } // Sets multiple values if ( typeof key === "object" ) { return this.each( function() { dataUser.set( this, key ); } ); } return access( this, function( value ) { var data; // The calling jQuery object (element matches) is not empty // (and therefore has an element appears at this[ 0 ]) and the // `value` parameter was not undefined. An empty jQuery object // will result in `undefined` for elem = this[ 0 ] which will // throw an exception if an attempt to read a data cache is made. if ( elem && value === undefined ) { // Attempt to get data from the cache // The key will always be camelCased in Data data = dataUser.get( elem, key ); if ( data !== undefined ) { return data; } // Attempt to "discover" the data in // HTML5 custom data-* attrs data = dataAttr( elem, key ); if ( data !== undefined ) { return data; } // We tried really hard, but the data doesn't exist. return; } // Set the data... this.each( function() { // We always store the camelCased key dataUser.set( this, key, value ); } ); }, null, value, arguments.length > 1, null, true ); }, removeData: function( key ) { return this.each( function() { dataUser.remove( this, key ); } ); } } ); jQuery.extend( { queue: function( elem, type, data ) { var queue; if ( elem ) { type = ( type || "fx" ) + "queue"; queue = dataPriv.get( elem, type ); // Speed up dequeue by getting out quickly if this is just a lookup if ( data ) { if ( !queue || Array.isArray( data ) ) { queue = dataPriv.access( elem, type, jQuery.makeArray( data ) ); } else { queue.push( data ); } } return queue || []; } }, dequeue: function( elem, type ) { type = type || "fx"; var queue = jQuery.queue( elem, type ), startLength = queue.length, fn = queue.shift(), hooks = jQuery._queueHooks( elem, type ), next = function() { jQuery.dequeue( elem, type ); }; // If the fx queue is dequeued, always remove the progress sentinel if ( fn === "inprogress" ) { fn = queue.shift(); startLength--; } if ( fn ) { // Add a progress sentinel to prevent the fx queue from being // automatically dequeued if ( type === "fx" ) { queue.unshift( "inprogress" ); } // Clear up the last queue stop function delete hooks.stop; fn.call( elem, next, hooks ); } if ( !startLength && hooks ) { hooks.empty.fire(); } }, // Not public - generate a queueHooks object, or return the current one _queueHooks: function( elem, type ) { var key = type + "queueHooks"; return dataPriv.get( elem, key ) || dataPriv.access( elem, key, { empty: jQuery.Callbacks( "once memory" ).add( function() { dataPriv.remove( elem, [ type + "queue", key ] ); } ) } ); } } ); jQuery.fn.extend( { queue: function( type, data ) { var setter = 2; if ( typeof type !== "string" ) { data = type; type = "fx"; setter--; } if ( arguments.length < setter ) { return jQuery.queue( this[ 0 ], type ); } return data === undefined ? this : this.each( function() { var queue = jQuery.queue( this, type, data ); // Ensure a hooks for this queue jQuery._queueHooks( this, type ); if ( type === "fx" && queue[ 0 ] !== "inprogress" ) { jQuery.dequeue( this, type ); } } ); }, dequeue: function( type ) { return this.each( function() { jQuery.dequeue( this, type ); } ); }, clearQueue: function( type ) { return this.queue( type || "fx", [] ); }, // Get a promise resolved when queues of a certain type // are emptied (fx is the type by default) promise: function( type, obj ) { var tmp, count = 1, defer = jQuery.Deferred(), elements = this, i = this.length, resolve = function() { if ( !( --count ) ) { defer.resolveWith( elements, [ elements ] ); } }; if ( typeof type !== "string" ) { obj = type; type = undefined; } type = type || "fx"; while ( i-- ) { tmp = dataPriv.get( elements[ i ], type + "queueHooks" ); if ( tmp && tmp.empty ) { count++; tmp.empty.add( resolve ); } } resolve(); return defer.promise( obj ); } } ); var pnum = ( /[+-]?(?:\d*\.|)\d+(?:[eE][+-]?\d+|)/ ).source; var rcssNum = new RegExp( "^(?:([+-])=|)(" + pnum + ")([a-z%]*)$", "i" ); var cssExpand = [ "Top", "Right", "Bottom", "Left" ]; var documentElement = document.documentElement; var isAttached = function( elem ) { return jQuery.contains( elem.ownerDocument, elem ); }, composed = { composed: true }; // Support: IE 9 - 11+, Edge 12 - 18+, iOS 10.0 - 10.2 only // Check attachment across shadow DOM boundaries when possible (gh-3504) // Support: iOS 10.0-10.2 only // Early iOS 10 versions support `attachShadow` but not `getRootNode`, // leading to errors. We need to check for `getRootNode`. if ( documentElement.getRootNode ) { isAttached = function( elem ) { return jQuery.contains( elem.ownerDocument, elem ) || elem.getRootNode( composed ) === elem.ownerDocument; }; } var isHiddenWithinTree = function( elem, el ) { // isHiddenWithinTree might be called from jQuery#filter function; // in that case, element will be second argument elem = el || elem; // Inline style trumps all return elem.style.display === "none" || elem.style.display === "" && // Otherwise, check computed style // Support: Firefox <=43 - 45 // Disconnected elements can have computed display: none, so first confirm that elem is // in the document. isAttached( elem ) && jQuery.css( elem, "display" ) === "none"; }; function adjustCSS( elem, prop, valueParts, tween ) { var adjusted, scale, maxIterations = 20, currentValue = tween ? function() { return tween.cur(); } : function() { return jQuery.css( elem, prop, "" ); }, initial = currentValue(), unit = valueParts && valueParts[ 3 ] || ( jQuery.cssNumber[ prop ] ? "" : "px" ), // Starting value computation is required for potential unit mismatches initialInUnit = elem.nodeType && ( jQuery.cssNumber[ prop ] || unit !== "px" && +initial ) && rcssNum.exec( jQuery.css( elem, prop ) ); if ( initialInUnit && initialInUnit[ 3 ] !== unit ) { // Support: Firefox <=54 // Halve the iteration target value to prevent interference from CSS upper bounds (gh-2144) initial = initial / 2; // Trust units reported by jQuery.css unit = unit || initialInUnit[ 3 ]; // Iteratively approximate from a nonzero starting point initialInUnit = +initial || 1; while ( maxIterations-- ) { // Evaluate and update our best guess (doubling guesses that zero out). // Finish if the scale equals or crosses 1 (making the old*new product non-positive). jQuery.style( elem, prop, initialInUnit + unit ); if ( ( 1 - scale ) * ( 1 - ( scale = currentValue() / initial || 0.5 ) ) <= 0 ) { maxIterations = 0; } initialInUnit = initialInUnit / scale; } initialInUnit = initialInUnit * 2; jQuery.style( elem, prop, initialInUnit + unit ); // Make sure we update the tween properties later on valueParts = valueParts || []; } if ( valueParts ) { initialInUnit = +initialInUnit || +initial || 0; // Apply relative offset (+=/-=) if specified adjusted = valueParts[ 1 ] ? initialInUnit + ( valueParts[ 1 ] + 1 ) * valueParts[ 2 ] : +valueParts[ 2 ]; if ( tween ) { tween.unit = unit; tween.start = initialInUnit; tween.end = adjusted; } } return adjusted; } var defaultDisplayMap = {}; function getDefaultDisplay( elem ) { var temp, doc = elem.ownerDocument, nodeName = elem.nodeName, display = defaultDisplayMap[ nodeName ]; if ( display ) { return display; } temp = doc.body.appendChild( doc.createElement( nodeName ) ); display = jQuery.css( temp, "display" ); temp.parentNode.removeChild( temp ); if ( display === "none" ) { display = "block"; } defaultDisplayMap[ nodeName ] = display; return display; } function showHide( elements, show ) { var display, elem, values = [], index = 0, length = elements.length; // Determine new display value for elements that need to change for ( ; index < length; index++ ) { elem = elements[ index ]; if ( !elem.style ) { continue; } display = elem.style.display; if ( show ) { // Since we force visibility upon cascade-hidden elements, an immediate (and slow) // check is required in this first loop unless we have a nonempty display value (either // inline or about-to-be-restored) if ( display === "none" ) { values[ index ] = dataPriv.get( elem, "display" ) || null; if ( !values[ index ] ) { elem.style.display = ""; } } if ( elem.style.display === "" && isHiddenWithinTree( elem ) ) { values[ index ] = getDefaultDisplay( elem ); } } else { if ( display !== "none" ) { values[ index ] = "none"; // Remember what we're overwriting dataPriv.set( elem, "display", display ); } } } // Set the display of the elements in a second loop to avoid constant reflow for ( index = 0; index < length; index++ ) { if ( values[ index ] != null ) { elements[ index ].style.display = values[ index ]; } } return elements; } jQuery.fn.extend( { show: function() { return showHide( this, true ); }, hide: function() { return showHide( this ); }, toggle: function( state ) { if ( typeof state === "boolean" ) { return state ? this.show() : this.hide(); } return this.each( function() { if ( isHiddenWithinTree( this ) ) { jQuery( this ).show(); } else { jQuery( this ).hide(); } } ); } } ); var rcheckableType = ( /^(?:checkbox|radio)$/i ); var rtagName = ( /<([a-z][^\/\0>\x20\t\r\n\f]*)/i ); var rscriptType = ( /^$|^module$|\/(?:java|ecma)script/i ); ( function() { var fragment = document.createDocumentFragment(), div = fragment.appendChild( document.createElement( "div" ) ), input = document.createElement( "input" ); // Support: Android 4.0 - 4.3 only // Check state lost if the name is set (#11217) // Support: Windows Web Apps (WWA) // `name` and `type` must use .setAttribute for WWA (#14901) input.setAttribute( "type", "radio" ); input.setAttribute( "checked", "checked" ); input.setAttribute( "name", "t" ); div.appendChild( input ); // Support: Android <=4.1 only // Older WebKit doesn't clone checked state correctly in fragments support.checkClone = div.cloneNode( true ).cloneNode( true ).lastChild.checked; // Support: IE <=11 only // Make sure textarea (and checkbox) defaultValue is properly cloned div.innerHTML = "<textarea>x</textarea>"; support.noCloneChecked = !!div.cloneNode( true ).lastChild.defaultValue; // Support: IE <=9 only // IE <=9 replaces <option> tags with their contents when inserted outside of // the select element. div.innerHTML = "<option></option>"; support.option = !!div.lastChild; } )(); // We have to close these tags to support XHTML (#13200) var wrapMap = { // XHTML parsers do not magically insert elements in the // same way that tag soup parsers do. So we cannot shorten // this by omitting <tbody> or other required elements. thead: [ 1, "<table>", "</table>" ], col: [ 2, "<table><colgroup>", "</colgroup></table>" ], tr: [ 2, "<table><tbody>", "</tbody></table>" ], td: [ 3, "<table><tbody><tr>", "</tr></tbody></table>" ], _default: [ 0, "", "" ] }; wrapMap.tbody = wrapMap.tfoot = wrapMap.colgroup = wrapMap.caption = wrapMap.thead; wrapMap.th = wrapMap.td; // Support: IE <=9 only if ( !support.option ) { wrapMap.optgroup = wrapMap.option = [ 1, "<select multiple='multiple'>", "</select>" ]; } function getAll( context, tag ) { // Support: IE <=9 - 11 only // Use typeof to avoid zero-argument method invocation on host objects (#15151) var ret; if ( typeof context.getElementsByTagName !== "undefined" ) { ret = context.getElementsByTagName( tag || "*" ); } else if ( typeof context.querySelectorAll !== "undefined" ) { ret = context.querySelectorAll( tag || "*" ); } else { ret = []; } if ( tag === undefined || tag && nodeName( context, tag ) ) { return jQuery.merge( [ context ], ret ); } return ret; } // Mark scripts as having already been evaluated function setGlobalEval( elems, refElements ) { var i = 0, l = elems.length; for ( ; i < l; i++ ) { dataPriv.set( elems[ i ], "globalEval", !refElements || dataPriv.get( refElements[ i ], "globalEval" ) ); } } var rhtml = /<|&#?\w+;/; function buildFragment( elems, context, scripts, selection, ignored ) { var elem, tmp, tag, wrap, attached, j, fragment = context.createDocumentFragment(), nodes = [], i = 0, l = elems.length; for ( ; i < l; i++ ) { elem = elems[ i ]; if ( elem || elem === 0 ) { // Add nodes directly if ( toType( elem ) === "object" ) { // Support: Android <=4.0 only, PhantomJS 1 only // push.apply(_, arraylike) throws on ancient WebKit jQuery.merge( nodes, elem.nodeType ? [ elem ] : elem ); // Convert non-html into a text node } else if ( !rhtml.test( elem ) ) { nodes.push( context.createTextNode( elem ) ); // Convert html into DOM nodes } else { tmp = tmp || fragment.appendChild( context.createElement( "div" ) ); // Deserialize a standard representation tag = ( rtagName.exec( elem ) || [ "", "" ] )[ 1 ].toLowerCase(); wrap = wrapMap[ tag ] || wrapMap._default; tmp.innerHTML = wrap[ 1 ] + jQuery.htmlPrefilter( elem ) + wrap[ 2 ]; // Descend through wrappers to the right content j = wrap[ 0 ]; while ( j-- ) { tmp = tmp.lastChild; } // Support: Android <=4.0 only, PhantomJS 1 only // push.apply(_, arraylike) throws on ancient WebKit jQuery.merge( nodes, tmp.childNodes ); // Remember the top-level container tmp = fragment.firstChild; // Ensure the created nodes are orphaned (#12392) tmp.textContent = ""; } } } // Remove wrapper from fragment fragment.textContent = ""; i = 0; while ( ( elem = nodes[ i++ ] ) ) { // Skip elements already in the context collection (trac-4087) if ( selection && jQuery.inArray( elem, selection ) > -1 ) { if ( ignored ) { ignored.push( elem ); } continue; } attached = isAttached( elem ); // Append to fragment tmp = getAll( fragment.appendChild( elem ), "script" ); // Preserve script evaluation history if ( attached ) { setGlobalEval( tmp ); } // Capture executables if ( scripts ) { j = 0; while ( ( elem = tmp[ j++ ] ) ) { if ( rscriptType.test( elem.type || "" ) ) { scripts.push( elem ); } } } } return fragment; } var rtypenamespace = /^([^.]*)(?:\.(.+)|)/; function returnTrue() { return true; } function returnFalse() { return false; } // Support: IE <=9 - 11+ // focus() and blur() are asynchronous, except when they are no-op. // So expect focus to be synchronous when the element is already active, // and blur to be synchronous when the element is not already active. // (focus and blur are always synchronous in other supported browsers, // this just defines when we can count on it). function expectSync( elem, type ) { return ( elem === safeActiveElement() ) === ( type === "focus" ); } // Support: IE <=9 only // Accessing document.activeElement can throw unexpectedly // https://bugs.jquery.com/ticket/13393 function safeActiveElement() { try { return document.activeElement; } catch ( err ) { } } function on( elem, types, selector, data, fn, one ) { var origFn, type; // Types can be a map of types/handlers if ( typeof types === "object" ) { // ( types-Object, selector, data ) if ( typeof selector !== "string" ) { // ( types-Object, data ) data = data || selector; selector = undefined; } for ( type in types ) { on( elem, type, selector, data, types[ type ], one ); } return elem; } if ( data == null && fn == null ) { // ( types, fn ) fn = selector; data = selector = undefined; } else if ( fn == null ) { if ( typeof selector === "string" ) { // ( types, selector, fn ) fn = data; data = undefined; } else { // ( types, data, fn ) fn = data; data = selector; selector = undefined; } } if ( fn === false ) { fn = returnFalse; } else if ( !fn ) { return elem; } if ( one === 1 ) { origFn = fn; fn = function( event ) { // Can use an empty set, since event contains the info jQuery().off( event ); return origFn.apply( this, arguments ); }; // Use same guid so caller can remove using origFn fn.guid = origFn.guid || ( origFn.guid = jQuery.guid++ ); } return elem.each( function() { jQuery.event.add( this, types, fn, data, selector ); } ); } /* * Helper functions for managing events -- not part of the public interface. * Props to Dean Edwards' addEvent library for many of the ideas. */ jQuery.event = { global: {}, add: function( elem, types, handler, data, selector ) { var handleObjIn, eventHandle, tmp, events, t, handleObj, special, handlers, type, namespaces, origType, elemData = dataPriv.get( elem ); // Only attach events to objects that accept data if ( !acceptData( elem ) ) { return; } // Caller can pass in an object of custom data in lieu of the handler if ( handler.handler ) { handleObjIn = handler; handler = handleObjIn.handler; selector = handleObjIn.selector; } // Ensure that invalid selectors throw exceptions at attach time // Evaluate against documentElement in case elem is a non-element node (e.g., document) if ( selector ) { jQuery.find.matchesSelector( documentElement, selector ); } // Make sure that the handler has a unique ID, used to find/remove it later if ( !handler.guid ) { handler.guid = jQuery.guid++; } // Init the element's event structure and main handler, if this is the first if ( !( events = elemData.events ) ) { events = elemData.events = Object.create( null ); } if ( !( eventHandle = elemData.handle ) ) { eventHandle = elemData.handle = function( e ) { // Discard the second event of a jQuery.event.trigger() and // when an event is called after a page has unloaded return typeof jQuery !== "undefined" && jQuery.event.triggered !== e.type ? jQuery.event.dispatch.apply( elem, arguments ) : undefined; }; } // Handle multiple events separated by a space types = ( types || "" ).match( rnothtmlwhite ) || [ "" ]; t = types.length; while ( t-- ) { tmp = rtypenamespace.exec( types[ t ] ) || []; type = origType = tmp[ 1 ]; namespaces = ( tmp[ 2 ] || "" ).split( "." ).sort(); // There *must* be a type, no attaching namespace-only handlers if ( !type ) { continue; } // If event changes its type, use the special event handlers for the changed type special = jQuery.event.special[ type ] || {}; // If selector defined, determine special event api type, otherwise given type type = ( selector ? special.delegateType : special.bindType ) || type; // Update special based on newly reset type special = jQuery.event.special[ type ] || {}; // handleObj is passed to all event handlers handleObj = jQuery.extend( { type: type, origType: origType, data: data, handler: handler, guid: handler.guid, selector: selector, needsContext: selector && jQuery.expr.match.needsContext.test( selector ), namespace: namespaces.join( "." ) }, handleObjIn ); // Init the event handler queue if we're the first if ( !( handlers = events[ type ] ) ) { handlers = events[ type ] = []; handlers.delegateCount = 0; // Only use addEventListener if the special events handler returns false if ( !special.setup || special.setup.call( elem, data, namespaces, eventHandle ) === false ) { if ( elem.addEventListener ) { elem.addEventListener( type, eventHandle ); } } } if ( special.add ) { special.add.call( elem, handleObj ); if ( !handleObj.handler.guid ) { handleObj.handler.guid = handler.guid; } } // Add to the element's handler list, delegates in front if ( selector ) { handlers.splice( handlers.delegateCount++, 0, handleObj ); } else { handlers.push( handleObj ); } // Keep track of which events have ever been used, for event optimization jQuery.event.global[ type ] = true; } }, // Detach an event or set of events from an element remove: function( elem, types, handler, selector, mappedTypes ) { var j, origCount, tmp, events, t, handleObj, special, handlers, type, namespaces, origType, elemData = dataPriv.hasData( elem ) && dataPriv.get( elem ); if ( !elemData || !( events = elemData.events ) ) { return; } // Once for each type.namespace in types; type may be omitted types = ( types || "" ).match( rnothtmlwhite ) || [ "" ]; t = types.length; while ( t-- ) { tmp = rtypenamespace.exec( types[ t ] ) || []; type = origType = tmp[ 1 ]; namespaces = ( tmp[ 2 ] || "" ).split( "." ).sort(); // Unbind all events (on this namespace, if provided) for the element if ( !type ) { for ( type in events ) { jQuery.event.remove( elem, type + types[ t ], handler, selector, true ); } continue; } special = jQuery.event.special[ type ] || {}; type = ( selector ? special.delegateType : special.bindType ) || type; handlers = events[ type ] || []; tmp = tmp[ 2 ] && new RegExp( "(^|\\.)" + namespaces.join( "\\.(?:.*\\.|)" ) + "(\\.|$)" ); // Remove matching events origCount = j = handlers.length; while ( j-- ) { handleObj = handlers[ j ]; if ( ( mappedTypes || origType === handleObj.origType ) && ( !handler || handler.guid === handleObj.guid ) && ( !tmp || tmp.test( handleObj.namespace ) ) && ( !selector || selector === handleObj.selector || selector === "**" && handleObj.selector ) ) { handlers.splice( j, 1 ); if ( handleObj.selector ) { handlers.delegateCount--; } if ( special.remove ) { special.remove.call( elem, handleObj ); } } } // Remove generic event handler if we removed something and no more handlers exist // (avoids potential for endless recursion during removal of special event handlers) if ( origCount && !handlers.length ) { if ( !special.teardown || special.teardown.call( elem, namespaces, elemData.handle ) === false ) { jQuery.removeEvent( elem, type, elemData.handle ); } delete events[ type ]; } } // Remove data and the expando if it's no longer used if ( jQuery.isEmptyObject( events ) ) { dataPriv.remove( elem, "handle events" ); } }, dispatch: function( nativeEvent ) { var i, j, ret, matched, handleObj, handlerQueue, args = new Array( arguments.length ), // Make a writable jQuery.Event from the native event object event = jQuery.event.fix( nativeEvent ), handlers = ( dataPriv.get( this, "events" ) || Object.create( null ) )[ event.type ] || [], special = jQuery.event.special[ event.type ] || {}; // Use the fix-ed jQuery.Event rather than the (read-only) native event args[ 0 ] = event; for ( i = 1; i < arguments.length; i++ ) { args[ i ] = arguments[ i ]; } event.delegateTarget = this; // Call the preDispatch hook for the mapped type, and let it bail if desired if ( special.preDispatch && special.preDispatch.call( this, event ) === false ) { return; } // Determine handlers handlerQueue = jQuery.event.handlers.call( this, event, handlers ); // Run delegates first; they may want to stop propagation beneath us i = 0; while ( ( matched = handlerQueue[ i++ ] ) && !event.isPropagationStopped() ) { event.currentTarget = matched.elem; j = 0; while ( ( handleObj = matched.handlers[ j++ ] ) && !event.isImmediatePropagationStopped() ) { // If the event is namespaced, then each handler is only invoked if it is // specially universal or its namespaces are a superset of the event's. if ( !event.rnamespace || handleObj.namespace === false || event.rnamespace.test( handleObj.namespace ) ) { event.handleObj = handleObj; event.data = handleObj.data; ret = ( ( jQuery.event.special[ handleObj.origType ] || {} ).handle || handleObj.handler ).apply( matched.elem, args ); if ( ret !== undefined ) { if ( ( event.result = ret ) === false ) { event.preventDefault(); event.stopPropagation(); } } } } } // Call the postDispatch hook for the mapped type if ( special.postDispatch ) { special.postDispatch.call( this, event ); } return event.result; }, handlers: function( event, handlers ) { var i, handleObj, sel, matchedHandlers, matchedSelectors, handlerQueue = [], delegateCount = handlers.delegateCount, cur = event.target; // Find delegate handlers if ( delegateCount && // Support: IE <=9 // Black-hole SVG <use> instance trees (trac-13180) cur.nodeType && // Support: Firefox <=42 // Suppress spec-violating clicks indicating a non-primary pointer button (trac-3861) // https://www.w3.org/TR/DOM-Level-3-Events/#event-type-click // Support: IE 11 only // ...but not arrow key "clicks" of radio inputs, which can have `button` -1 (gh-2343) !( event.type === "click" && event.button >= 1 ) ) { for ( ; cur !== this; cur = cur.parentNode || this ) { // Don't check non-elements (#13208) // Don't process clicks on disabled elements (#6911, #8165, #11382, #11764) if ( cur.nodeType === 1 && !( event.type === "click" && cur.disabled === true ) ) { matchedHandlers = []; matchedSelectors = {}; for ( i = 0; i < delegateCount; i++ ) { handleObj = handlers[ i ]; // Don't conflict with Object.prototype properties (#13203) sel = handleObj.selector + " "; if ( matchedSelectors[ sel ] === undefined ) { matchedSelectors[ sel ] = handleObj.needsContext ? jQuery( sel, this ).index( cur ) > -1 : jQuery.find( sel, this, null, [ cur ] ).length; } if ( matchedSelectors[ sel ] ) { matchedHandlers.push( handleObj ); } } if ( matchedHandlers.length ) { handlerQueue.push( { elem: cur, handlers: matchedHandlers } ); } } } } // Add the remaining (directly-bound) handlers cur = this; if ( delegateCount < handlers.length ) { handlerQueue.push( { elem: cur, handlers: handlers.slice( delegateCount ) } ); } return handlerQueue; }, addProp: function( name, hook ) { Object.defineProperty( jQuery.Event.prototype, name, { enumerable: true, configurable: true, get: isFunction( hook ) ? function() { if ( this.originalEvent ) { return hook( this.originalEvent ); } } : function() { if ( this.originalEvent ) { return this.originalEvent[ name ]; } }, set: function( value ) { Object.defineProperty( this, name, { enumerable: true, configurable: true, writable: true, value: value } ); } } ); }, fix: function( originalEvent ) { return originalEvent[ jQuery.expando ] ? originalEvent : new jQuery.Event( originalEvent ); }, special: { load: { // Prevent triggered image.load events from bubbling to window.load noBubble: true }, click: { // Utilize native event to ensure correct state for checkable inputs setup: function( data ) { // For mutual compressibility with _default, replace `this` access with a local var. // `|| data` is dead code meant only to preserve the variable through minification. var el = this || data; // Claim the first handler if ( rcheckableType.test( el.type ) && el.click && nodeName( el, "input" ) ) { // dataPriv.set( el, "click", ... ) leverageNative( el, "click", returnTrue ); } // Return false to allow normal processing in the caller return false; }, trigger: function( data ) { // For mutual compressibility with _default, replace `this` access with a local var. // `|| data` is dead code meant only to preserve the variable through minification. var el = this || data; // Force setup before triggering a click if ( rcheckableType.test( el.type ) && el.click && nodeName( el, "input" ) ) { leverageNative( el, "click" ); } // Return non-false to allow normal event-path propagation return true; }, // For cross-browser consistency, suppress native .click() on links // Also prevent it if we're currently inside a leveraged native-event stack _default: function( event ) { var target = event.target; return rcheckableType.test( target.type ) && target.click && nodeName( target, "input" ) && dataPriv.get( target, "click" ) || nodeName( target, "a" ); } }, beforeunload: { postDispatch: function( event ) { // Support: Firefox 20+ // Firefox doesn't alert if the returnValue field is not set. if ( event.result !== undefined && event.originalEvent ) { event.originalEvent.returnValue = event.result; } } } } }; // Ensure the presence of an event listener that handles manually-triggered // synthetic events by interrupting progress until reinvoked in response to // *native* events that it fires directly, ensuring that state changes have // already occurred before other listeners are invoked. function leverageNative( el, type, expectSync ) { // Missing expectSync indicates a trigger call, which must force setup through jQuery.event.add if ( !expectSync ) { if ( dataPriv.get( el, type ) === undefined ) { jQuery.event.add( el, type, returnTrue ); } return; } // Register the controller as a special universal handler for all event namespaces dataPriv.set( el, type, false ); jQuery.event.add( el, type, { namespace: false, handler: function( event ) { var notAsync, result, saved = dataPriv.get( this, type ); if ( ( event.isTrigger & 1 ) && this[ type ] ) { // Interrupt processing of the outer synthetic .trigger()ed event // Saved data should be false in such cases, but might be a leftover capture object // from an async native handler (gh-4350) if ( !saved.length ) { // Store arguments for use when handling the inner native event // There will always be at least one argument (an event object), so this array // will not be confused with a leftover capture object. saved = slice.call( arguments ); dataPriv.set( this, type, saved ); // Trigger the native event and capture its result // Support: IE <=9 - 11+ // focus() and blur() are asynchronous notAsync = expectSync( this, type ); this[ type ](); result = dataPriv.get( this, type ); if ( saved !== result || notAsync ) { dataPriv.set( this, type, false ); } else { result = {}; } if ( saved !== result ) { // Cancel the outer synthetic event event.stopImmediatePropagation(); event.preventDefault(); // Support: Chrome 86+ // In Chrome, if an element having a focusout handler is blurred by // clicking outside of it, it invokes the handler synchronously. If // that handler calls `.remove()` on the element, the data is cleared, // leaving `result` undefined. We need to guard against this. return result && result.value; } // If this is an inner synthetic event for an event with a bubbling surrogate // (focus or blur), assume that the surrogate already propagated from triggering the // native event and prevent that from happening again here. // This technically gets the ordering wrong w.r.t. to `.trigger()` (in which the // bubbling surrogate propagates *after* the non-bubbling base), but that seems // less bad than duplication. } else if ( ( jQuery.event.special[ type ] || {} ).delegateType ) { event.stopPropagation(); } // If this is a native event triggered above, everything is now in order // Fire an inner synthetic event with the original arguments } else if ( saved.length ) { // ...and capture the result dataPriv.set( this, type, { value: jQuery.event.trigger( // Support: IE <=9 - 11+ // Extend with the prototype to reset the above stopImmediatePropagation() jQuery.extend( saved[ 0 ], jQuery.Event.prototype ), saved.slice( 1 ), this ) } ); // Abort handling of the native event event.stopImmediatePropagation(); } } } ); } jQuery.removeEvent = function( elem, type, handle ) { // This "if" is needed for plain objects if ( elem.removeEventListener ) { elem.removeEventListener( type, handle ); } }; jQuery.Event = function( src, props ) { // Allow instantiation without the 'new' keyword if ( !( this instanceof jQuery.Event ) ) { return new jQuery.Event( src, props ); } // Event object if ( src && src.type ) { this.originalEvent = src; this.type = src.type; // Events bubbling up the document may have been marked as prevented // by a handler lower down the tree; reflect the correct value. this.isDefaultPrevented = src.defaultPrevented || src.defaultPrevented === undefined && // Support: Android <=2.3 only src.returnValue === false ? returnTrue : returnFalse; // Create target properties // Support: Safari <=6 - 7 only // Target should not be a text node (#504, #13143) this.target = ( src.target && src.target.nodeType === 3 ) ? src.target.parentNode : src.target; this.currentTarget = src.currentTarget; this.relatedTarget = src.relatedTarget; // Event type } else { this.type = src; } // Put explicitly provided properties onto the event object if ( props ) { jQuery.extend( this, props ); } // Create a timestamp if incoming event doesn't have one this.timeStamp = src && src.timeStamp || Date.now(); // Mark it as fixed this[ jQuery.expando ] = true; }; // jQuery.Event is based on DOM3 Events as specified by the ECMAScript Language Binding // https://www.w3.org/TR/2003/WD-DOM-Level-3-Events-20030331/ecma-script-binding.html jQuery.Event.prototype = { constructor: jQuery.Event, isDefaultPrevented: returnFalse, isPropagationStopped: returnFalse, isImmediatePropagationStopped: returnFalse, isSimulated: false, preventDefault: function() { var e = this.originalEvent; this.isDefaultPrevented = returnTrue; if ( e && !this.isSimulated ) { e.preventDefault(); } }, stopPropagation: function() { var e = this.originalEvent; this.isPropagationStopped = returnTrue; if ( e && !this.isSimulated ) { e.stopPropagation(); } }, stopImmediatePropagation: function() { var e = this.originalEvent; this.isImmediatePropagationStopped = returnTrue; if ( e && !this.isSimulated ) { e.stopImmediatePropagation(); } this.stopPropagation(); } }; // Includes all common event props including KeyEvent and MouseEvent specific props jQuery.each( { altKey: true, bubbles: true, cancelable: true, changedTouches: true, ctrlKey: true, detail: true, eventPhase: true, metaKey: true, pageX: true, pageY: true, shiftKey: true, view: true, "char": true, code: true, charCode: true, key: true, keyCode: true, button: true, buttons: true, clientX: true, clientY: true, offsetX: true, offsetY: true, pointerId: true, pointerType: true, screenX: true, screenY: true, targetTouches: true, toElement: true, touches: true, which: true }, jQuery.event.addProp ); jQuery.each( { focus: "focusin", blur: "focusout" }, function( type, delegateType ) { jQuery.event.special[ type ] = { // Utilize native event if possible so blur/focus sequence is correct setup: function() { // Claim the first handler // dataPriv.set( this, "focus", ... ) // dataPriv.set( this, "blur", ... ) leverageNative( this, type, expectSync ); // Return false to allow normal processing in the caller return false; }, trigger: function() { // Force setup before trigger leverageNative( this, type ); // Return non-false to allow normal event-path propagation return true; }, // Suppress native focus or blur as it's already being fired // in leverageNative. _default: function() { return true; }, delegateType: delegateType }; } ); // Create mouseenter/leave events using mouseover/out and event-time checks // so that event delegation works in jQuery. // Do the same for pointerenter/pointerleave and pointerover/pointerout // // Support: Safari 7 only // Safari sends mouseenter too often; see: // https://bugs.chromium.org/p/chromium/issues/detail?id=470258 // for the description of the bug (it existed in older Chrome versions as well). jQuery.each( { mouseenter: "mouseover", mouseleave: "mouseout", pointerenter: "pointerover", pointerleave: "pointerout" }, function( orig, fix ) { jQuery.event.special[ orig ] = { delegateType: fix, bindType: fix, handle: function( event ) { var ret, target = this, related = event.relatedTarget, handleObj = event.handleObj; // For mouseenter/leave call the handler if related is outside the target. // NB: No relatedTarget if the mouse left/entered the browser window if ( !related || ( related !== target && !jQuery.contains( target, related ) ) ) { event.type = handleObj.origType; ret = handleObj.handler.apply( this, arguments ); event.type = fix; } return ret; } }; } ); jQuery.fn.extend( { on: function( types, selector, data, fn ) { return on( this, types, selector, data, fn ); }, one: function( types, selector, data, fn ) { return on( this, types, selector, data, fn, 1 ); }, off: function( types, selector, fn ) { var handleObj, type; if ( types && types.preventDefault && types.handleObj ) { // ( event ) dispatched jQuery.Event handleObj = types.handleObj; jQuery( types.delegateTarget ).off( handleObj.namespace ? handleObj.origType + "." + handleObj.namespace : handleObj.origType, handleObj.selector, handleObj.handler ); return this; } if ( typeof types === "object" ) { // ( types-object [, selector] ) for ( type in types ) { this.off( type, selector, types[ type ] ); } return this; } if ( selector === false || typeof selector === "function" ) { // ( types [, fn] ) fn = selector; selector = undefined; } if ( fn === false ) { fn = returnFalse; } return this.each( function() { jQuery.event.remove( this, types, fn, selector ); } ); } } ); var // Support: IE <=10 - 11, Edge 12 - 13 only // In IE/Edge using regex groups here causes severe slowdowns. // See https://connect.microsoft.com/IE/feedback/details/1736512/ rnoInnerhtml = /<script|<style|<link/i, // checked="checked" or checked rchecked = /checked\s*(?:[^=]|=\s*.checked.)/i, rcleanScript = /^\s*<!(?:\[CDATA\[|--)|(?:\]\]|--)>\s*$/g; // Prefer a tbody over its parent table for containing new rows function manipulationTarget( elem, content ) { if ( nodeName( elem, "table" ) && nodeName( content.nodeType !== 11 ? content : content.firstChild, "tr" ) ) { return jQuery( elem ).children( "tbody" )[ 0 ] || elem; } return elem; } // Replace/restore the type attribute of script elements for safe DOM manipulation function disableScript( elem ) { elem.type = ( elem.getAttribute( "type" ) !== null ) + "/" + elem.type; return elem; } function restoreScript( elem ) { if ( ( elem.type || "" ).slice( 0, 5 ) === "true/" ) { elem.type = elem.type.slice( 5 ); } else { elem.removeAttribute( "type" ); } return elem; } function cloneCopyEvent( src, dest ) { var i, l, type, pdataOld, udataOld, udataCur, events; if ( dest.nodeType !== 1 ) { return; } // 1. Copy private data: events, handlers, etc. if ( dataPriv.hasData( src ) ) { pdataOld = dataPriv.get( src ); events = pdataOld.events; if ( events ) { dataPriv.remove( dest, "handle events" ); for ( type in events ) { for ( i = 0, l = events[ type ].length; i < l; i++ ) { jQuery.event.add( dest, type, events[ type ][ i ] ); } } } } // 2. Copy user data if ( dataUser.hasData( src ) ) { udataOld = dataUser.access( src ); udataCur = jQuery.extend( {}, udataOld ); dataUser.set( dest, udataCur ); } } // Fix IE bugs, see support tests function fixInput( src, dest ) { var nodeName = dest.nodeName.toLowerCase(); // Fails to persist the checked state of a cloned checkbox or radio button. if ( nodeName === "input" && rcheckableType.test( src.type ) ) { dest.checked = src.checked; // Fails to return the selected option to the default selected state when cloning options } else if ( nodeName === "input" || nodeName === "textarea" ) { dest.defaultValue = src.defaultValue; } } function domManip( collection, args, callback, ignored ) { // Flatten any nested arrays args = flat( args ); var fragment, first, scripts, hasScripts, node, doc, i = 0, l = collection.length, iNoClone = l - 1, value = args[ 0 ], valueIsFunction = isFunction( value ); // We can't cloneNode fragments that contain checked, in WebKit if ( valueIsFunction || ( l > 1 && typeof value === "string" && !support.checkClone && rchecked.test( value ) ) ) { return collection.each( function( index ) { var self = collection.eq( index ); if ( valueIsFunction ) { args[ 0 ] = value.call( this, index, self.html() ); } domManip( self, args, callback, ignored ); } ); } if ( l ) { fragment = buildFragment( args, collection[ 0 ].ownerDocument, false, collection, ignored ); first = fragment.firstChild; if ( fragment.childNodes.length === 1 ) { fragment = first; } // Require either new content or an interest in ignored elements to invoke the callback if ( first || ignored ) { scripts = jQuery.map( getAll( fragment, "script" ), disableScript ); hasScripts = scripts.length; // Use the original fragment for the last item // instead of the first because it can end up // being emptied incorrectly in certain situations (#8070). for ( ; i < l; i++ ) { node = fragment; if ( i !== iNoClone ) { node = jQuery.clone( node, true, true ); // Keep references to cloned scripts for later restoration if ( hasScripts ) { // Support: Android <=4.0 only, PhantomJS 1 only // push.apply(_, arraylike) throws on ancient WebKit jQuery.merge( scripts, getAll( node, "script" ) ); } } callback.call( collection[ i ], node, i ); } if ( hasScripts ) { doc = scripts[ scripts.length - 1 ].ownerDocument; // Reenable scripts jQuery.map( scripts, restoreScript ); // Evaluate executable scripts on first document insertion for ( i = 0; i < hasScripts; i++ ) { node = scripts[ i ]; if ( rscriptType.test( node.type || "" ) && !dataPriv.access( node, "globalEval" ) && jQuery.contains( doc, node ) ) { if ( node.src && ( node.type || "" ).toLowerCase() !== "module" ) { // Optional AJAX dependency, but won't run scripts if not present if ( jQuery._evalUrl && !node.noModule ) { jQuery._evalUrl( node.src, { nonce: node.nonce || node.getAttribute( "nonce" ) }, doc ); } } else { DOMEval( node.textContent.replace( rcleanScript, "" ), node, doc ); } } } } } } return collection; } function remove( elem, selector, keepData ) { var node, nodes = selector ? jQuery.filter( selector, elem ) : elem, i = 0; for ( ; ( node = nodes[ i ] ) != null; i++ ) { if ( !keepData && node.nodeType === 1 ) { jQuery.cleanData( getAll( node ) ); } if ( node.parentNode ) { if ( keepData && isAttached( node ) ) { setGlobalEval( getAll( node, "script" ) ); } node.parentNode.removeChild( node ); } } return elem; } jQuery.extend( { htmlPrefilter: function( html ) { return html; }, clone: function( elem, dataAndEvents, deepDataAndEvents ) { var i, l, srcElements, destElements, clone = elem.cloneNode( true ), inPage = isAttached( elem ); // Fix IE cloning issues if ( !support.noCloneChecked && ( elem.nodeType === 1 || elem.nodeType === 11 ) && !jQuery.isXMLDoc( elem ) ) { // We eschew Sizzle here for performance reasons: https://jsperf.com/getall-vs-sizzle/2 destElements = getAll( clone ); srcElements = getAll( elem ); for ( i = 0, l = srcElements.length; i < l; i++ ) { fixInput( srcElements[ i ], destElements[ i ] ); } } // Copy the events from the original to the clone if ( dataAndEvents ) { if ( deepDataAndEvents ) { srcElements = srcElements || getAll( elem ); destElements = destElements || getAll( clone ); for ( i = 0, l = srcElements.length; i < l; i++ ) { cloneCopyEvent( srcElements[ i ], destElements[ i ] ); } } else { cloneCopyEvent( elem, clone ); } } // Preserve script evaluation history destElements = getAll( clone, "script" ); if ( destElements.length > 0 ) { setGlobalEval( destElements, !inPage && getAll( elem, "script" ) ); } // Return the cloned set return clone; }, cleanData: function( elems ) { var data, elem, type, special = jQuery.event.special, i = 0; for ( ; ( elem = elems[ i ] ) !== undefined; i++ ) { if ( acceptData( elem ) ) { if ( ( data = elem[ dataPriv.expando ] ) ) { if ( data.events ) { for ( type in data.events ) { if ( special[ type ] ) { jQuery.event.remove( elem, type ); // This is a shortcut to avoid jQuery.event.remove's overhead } else { jQuery.removeEvent( elem, type, data.handle ); } } } // Support: Chrome <=35 - 45+ // Assign undefined instead of using delete, see Data#remove elem[ dataPriv.expando ] = undefined; } if ( elem[ dataUser.expando ] ) { // Support: Chrome <=35 - 45+ // Assign undefined instead of using delete, see Data#remove elem[ dataUser.expando ] = undefined; } } } } } ); jQuery.fn.extend( { detach: function( selector ) { return remove( this, selector, true ); }, remove: function( selector ) { return remove( this, selector ); }, text: function( value ) { return access( this, function( value ) { return value === undefined ? jQuery.text( this ) : this.empty().each( function() { if ( this.nodeType === 1 || this.nodeType === 11 || this.nodeType === 9 ) { this.textContent = value; } } ); }, null, value, arguments.length ); }, append: function() { return domManip( this, arguments, function( elem ) { if ( this.nodeType === 1 || this.nodeType === 11 || this.nodeType === 9 ) { var target = manipulationTarget( this, elem ); target.appendChild( elem ); } } ); }, prepend: function() { return domManip( this, arguments, function( elem ) { if ( this.nodeType === 1 || this.nodeType === 11 || this.nodeType === 9 ) { var target = manipulationTarget( this, elem ); target.insertBefore( elem, target.firstChild ); } } ); }, before: function() { return domManip( this, arguments, function( elem ) { if ( this.parentNode ) { this.parentNode.insertBefore( elem, this ); } } ); }, after: function() { return domManip( this, arguments, function( elem ) { if ( this.parentNode ) { this.parentNode.insertBefore( elem, this.nextSibling ); } } ); }, empty: function() { var elem, i = 0; for ( ; ( elem = this[ i ] ) != null; i++ ) { if ( elem.nodeType === 1 ) { // Prevent memory leaks jQuery.cleanData( getAll( elem, false ) ); // Remove any remaining nodes elem.textContent = ""; } } return this; }, clone: function( dataAndEvents, deepDataAndEvents ) { dataAndEvents = dataAndEvents == null ? false : dataAndEvents; deepDataAndEvents = deepDataAndEvents == null ? dataAndEvents : deepDataAndEvents; return this.map( function() { return jQuery.clone( this, dataAndEvents, deepDataAndEvents ); } ); }, html: function( value ) { return access( this, function( value ) { var elem = this[ 0 ] || {}, i = 0, l = this.length; if ( value === undefined && elem.nodeType === 1 ) { return elem.innerHTML; } // See if we can take a shortcut and just use innerHTML if ( typeof value === "string" && !rnoInnerhtml.test( value ) && !wrapMap[ ( rtagName.exec( value ) || [ "", "" ] )[ 1 ].toLowerCase() ] ) { value = jQuery.htmlPrefilter( value ); try { for ( ; i < l; i++ ) { elem = this[ i ] || {}; // Remove element nodes and prevent memory leaks if ( elem.nodeType === 1 ) { jQuery.cleanData( getAll( elem, false ) ); elem.innerHTML = value; } } elem = 0; // If using innerHTML throws an exception, use the fallback method } catch ( e ) {} } if ( elem ) { this.empty().append( value ); } }, null, value, arguments.length ); }, replaceWith: function() { var ignored = []; // Make the changes, replacing each non-ignored context element with the new content return domManip( this, arguments, function( elem ) { var parent = this.parentNode; if ( jQuery.inArray( this, ignored ) < 0 ) { jQuery.cleanData( getAll( this ) ); if ( parent ) { parent.replaceChild( elem, this ); } } // Force callback invocation }, ignored ); } } ); jQuery.each( { appendTo: "append", prependTo: "prepend", insertBefore: "before", insertAfter: "after", replaceAll: "replaceWith" }, function( name, original ) { jQuery.fn[ name ] = function( selector ) { var elems, ret = [], insert = jQuery( selector ), last = insert.length - 1, i = 0; for ( ; i <= last; i++ ) { elems = i === last ? this : this.clone( true ); jQuery( insert[ i ] )[ original ]( elems ); // Support: Android <=4.0 only, PhantomJS 1 only // .get() because push.apply(_, arraylike) throws on ancient WebKit push.apply( ret, elems.get() ); } return this.pushStack( ret ); }; } ); var rnumnonpx = new RegExp( "^(" + pnum + ")(?!px)[a-z%]+$", "i" ); var getStyles = function( elem ) { // Support: IE <=11 only, Firefox <=30 (#15098, #14150) // IE throws on elements created in popups // FF meanwhile throws on frame elements through "defaultView.getComputedStyle" var view = elem.ownerDocument.defaultView; if ( !view || !view.opener ) { view = window; } return view.getComputedStyle( elem ); }; var swap = function( elem, options, callback ) { var ret, name, old = {}; // Remember the old values, and insert the new ones for ( name in options ) { old[ name ] = elem.style[ name ]; elem.style[ name ] = options[ name ]; } ret = callback.call( elem ); // Revert the old values for ( name in options ) { elem.style[ name ] = old[ name ]; } return ret; }; var rboxStyle = new RegExp( cssExpand.join( "|" ), "i" ); ( function() { // Executing both pixelPosition & boxSizingReliable tests require only one layout // so they're executed at the same time to save the second computation. function computeStyleTests() { // This is a singleton, we need to execute it only once if ( !div ) { return; } container.style.cssText = "position:absolute;left:-11111px;width:60px;" + "margin-top:1px;padding:0;border:0"; div.style.cssText = "position:relative;display:block;box-sizing:border-box;overflow:scroll;" + "margin:auto;border:1px;padding:1px;" + "width:60%;top:1%"; documentElement.appendChild( container ).appendChild( div ); var divStyle = window.getComputedStyle( div ); pixelPositionVal = divStyle.top !== "1%"; // Support: Android 4.0 - 4.3 only, Firefox <=3 - 44 reliableMarginLeftVal = roundPixelMeasures( divStyle.marginLeft ) === 12; // Support: Android 4.0 - 4.3 only, Safari <=9.1 - 10.1, iOS <=7.0 - 9.3 // Some styles come back with percentage values, even though they shouldn't div.style.right = "60%"; pixelBoxStylesVal = roundPixelMeasures( divStyle.right ) === 36; // Support: IE 9 - 11 only // Detect misreporting of content dimensions for box-sizing:border-box elements boxSizingReliableVal = roundPixelMeasures( divStyle.width ) === 36; // Support: IE 9 only // Detect overflow:scroll screwiness (gh-3699) // Support: Chrome <=64 // Don't get tricked when zoom affects offsetWidth (gh-4029) div.style.position = "absolute"; scrollboxSizeVal = roundPixelMeasures( div.offsetWidth / 3 ) === 12; documentElement.removeChild( container ); // Nullify the div so it wouldn't be stored in the memory and // it will also be a sign that checks already performed div = null; } function roundPixelMeasures( measure ) { return Math.round( parseFloat( measure ) ); } var pixelPositionVal, boxSizingReliableVal, scrollboxSizeVal, pixelBoxStylesVal, reliableTrDimensionsVal, reliableMarginLeftVal, container = document.createElement( "div" ), div = document.createElement( "div" ); // Finish early in limited (non-browser) environments if ( !div.style ) { return; } // Support: IE <=9 - 11 only // Style of cloned element affects source element cloned (#8908) div.style.backgroundClip = "content-box"; div.cloneNode( true ).style.backgroundClip = ""; support.clearCloneStyle = div.style.backgroundClip === "content-box"; jQuery.extend( support, { boxSizingReliable: function() { computeStyleTests(); return boxSizingReliableVal; }, pixelBoxStyles: function() { computeStyleTests(); return pixelBoxStylesVal; }, pixelPosition: function() { computeStyleTests(); return pixelPositionVal; }, reliableMarginLeft: function() { computeStyleTests(); return reliableMarginLeftVal; }, scrollboxSize: function() { computeStyleTests(); return scrollboxSizeVal; }, // Support: IE 9 - 11+, Edge 15 - 18+ // IE/Edge misreport `getComputedStyle` of table rows with width/height // set in CSS while `offset*` properties report correct values. // Behavior in IE 9 is more subtle than in newer versions & it passes // some versions of this test; make sure not to make it pass there! // // Support: Firefox 70+ // Only Firefox includes border widths // in computed dimensions. (gh-4529) reliableTrDimensions: function() { var table, tr, trChild, trStyle; if ( reliableTrDimensionsVal == null ) { table = document.createElement( "table" ); tr = document.createElement( "tr" ); trChild = document.createElement( "div" ); table.style.cssText = "position:absolute;left:-11111px;border-collapse:separate"; tr.style.cssText = "border:1px solid"; // Support: Chrome 86+ // Height set through cssText does not get applied. // Computed height then comes back as 0. tr.style.height = "1px"; trChild.style.height = "9px"; // Support: Android 8 Chrome 86+ // In our bodyBackground.html iframe, // display for all div elements is set to "inline", // which causes a problem only in Android 8 Chrome 86. // Ensuring the div is display: block // gets around this issue. trChild.style.display = "block"; documentElement .appendChild( table ) .appendChild( tr ) .appendChild( trChild ); trStyle = window.getComputedStyle( tr ); reliableTrDimensionsVal = ( parseInt( trStyle.height, 10 ) + parseInt( trStyle.borderTopWidth, 10 ) + parseInt( trStyle.borderBottomWidth, 10 ) ) === tr.offsetHeight; documentElement.removeChild( table ); } return reliableTrDimensionsVal; } } ); } )(); function curCSS( elem, name, computed ) { var width, minWidth, maxWidth, ret, // Support: Firefox 51+ // Retrieving style before computed somehow // fixes an issue with getting wrong values // on detached elements style = elem.style; computed = computed || getStyles( elem ); // getPropertyValue is needed for: // .css('filter') (IE 9 only, #12537) // .css('--customProperty) (#3144) if ( computed ) { ret = computed.getPropertyValue( name ) || computed[ name ]; if ( ret === "" && !isAttached( elem ) ) { ret = jQuery.style( elem, name ); } // A tribute to the "awesome hack by Dean Edwards" // Android Browser returns percentage for some values, // but width seems to be reliably pixels. // This is against the CSSOM draft spec: // https://drafts.csswg.org/cssom/#resolved-values if ( !support.pixelBoxStyles() && rnumnonpx.test( ret ) && rboxStyle.test( name ) ) { // Remember the original values width = style.width; minWidth = style.minWidth; maxWidth = style.maxWidth; // Put in the new values to get a computed value out style.minWidth = style.maxWidth = style.width = ret; ret = computed.width; // Revert the changed values style.width = width; style.minWidth = minWidth; style.maxWidth = maxWidth; } } return ret !== undefined ? // Support: IE <=9 - 11 only // IE returns zIndex value as an integer. ret + "" : ret; } function addGetHookIf( conditionFn, hookFn ) { // Define the hook, we'll check on the first run if it's really needed. return { get: function() { if ( conditionFn() ) { // Hook not needed (or it's not possible to use it due // to missing dependency), remove it. delete this.get; return; } // Hook needed; redefine it so that the support test is not executed again. return ( this.get = hookFn ).apply( this, arguments ); } }; } var cssPrefixes = [ "Webkit", "Moz", "ms" ], emptyStyle = document.createElement( "div" ).style, vendorProps = {}; // Return a vendor-prefixed property or undefined function vendorPropName( name ) { // Check for vendor prefixed names var capName = name[ 0 ].toUpperCase() + name.slice( 1 ), i = cssPrefixes.length; while ( i-- ) { name = cssPrefixes[ i ] + capName; if ( name in emptyStyle ) { return name; } } } // Return a potentially-mapped jQuery.cssProps or vendor prefixed property function finalPropName( name ) { var final = jQuery.cssProps[ name ] || vendorProps[ name ]; if ( final ) { return final; } if ( name in emptyStyle ) { return name; } return vendorProps[ name ] = vendorPropName( name ) || name; } var // Swappable if display is none or starts with table // except "table", "table-cell", or "table-caption" // See here for display values: https://developer.mozilla.org/en-US/docs/CSS/display rdisplayswap = /^(none|table(?!-c[ea]).+)/, rcustomProp = /^--/, cssShow = { position: "absolute", visibility: "hidden", display: "block" }, cssNormalTransform = { letterSpacing: "0", fontWeight: "400" }; function setPositiveNumber( _elem, value, subtract ) { // Any relative (+/-) values have already been // normalized at this point var matches = rcssNum.exec( value ); return matches ? // Guard against undefined "subtract", e.g., when used as in cssHooks Math.max( 0, matches[ 2 ] - ( subtract || 0 ) ) + ( matches[ 3 ] || "px" ) : value; } function boxModelAdjustment( elem, dimension, box, isBorderBox, styles, computedVal ) { var i = dimension === "width" ? 1 : 0, extra = 0, delta = 0; // Adjustment may not be necessary if ( box === ( isBorderBox ? "border" : "content" ) ) { return 0; } for ( ; i < 4; i += 2 ) { // Both box models exclude margin if ( box === "margin" ) { delta += jQuery.css( elem, box + cssExpand[ i ], true, styles ); } // If we get here with a content-box, we're seeking "padding" or "border" or "margin" if ( !isBorderBox ) { // Add padding delta += jQuery.css( elem, "padding" + cssExpand[ i ], true, styles ); // For "border" or "margin", add border if ( box !== "padding" ) { delta += jQuery.css( elem, "border" + cssExpand[ i ] + "Width", true, styles ); // But still keep track of it otherwise } else { extra += jQuery.css( elem, "border" + cssExpand[ i ] + "Width", true, styles ); } // If we get here with a border-box (content + padding + border), we're seeking "content" or // "padding" or "margin" } else { // For "content", subtract padding if ( box === "content" ) { delta -= jQuery.css( elem, "padding" + cssExpand[ i ], true, styles ); } // For "content" or "padding", subtract border if ( box !== "margin" ) { delta -= jQuery.css( elem, "border" + cssExpand[ i ] + "Width", true, styles ); } } } // Account for positive content-box scroll gutter when requested by providing computedVal if ( !isBorderBox && computedVal >= 0 ) { // offsetWidth/offsetHeight is a rounded sum of content, padding, scroll gutter, and border // Assuming integer scroll gutter, subtract the rest and round down delta += Math.max( 0, Math.ceil( elem[ "offset" + dimension[ 0 ].toUpperCase() + dimension.slice( 1 ) ] - computedVal - delta - extra - 0.5 // If offsetWidth/offsetHeight is unknown, then we can't determine content-box scroll gutter // Use an explicit zero to avoid NaN (gh-3964) ) ) || 0; } return delta; } function getWidthOrHeight( elem, dimension, extra ) { // Start with computed style var styles = getStyles( elem ), // To avoid forcing a reflow, only fetch boxSizing if we need it (gh-4322). // Fake content-box until we know it's needed to know the true value. boxSizingNeeded = !support.boxSizingReliable() || extra, isBorderBox = boxSizingNeeded && jQuery.css( elem, "boxSizing", false, styles ) === "border-box", valueIsBorderBox = isBorderBox, val = curCSS( elem, dimension, styles ), offsetProp = "offset" + dimension[ 0 ].toUpperCase() + dimension.slice( 1 ); // Support: Firefox <=54 // Return a confounding non-pixel value or feign ignorance, as appropriate. if ( rnumnonpx.test( val ) ) { if ( !extra ) { return val; } val = "auto"; } // Support: IE 9 - 11 only // Use offsetWidth/offsetHeight for when box sizing is unreliable. // In those cases, the computed value can be trusted to be border-box. if ( ( !support.boxSizingReliable() && isBorderBox || // Support: IE 10 - 11+, Edge 15 - 18+ // IE/Edge misreport `getComputedStyle` of table rows with width/height // set in CSS while `offset*` properties report correct values. // Interestingly, in some cases IE 9 doesn't suffer from this issue. !support.reliableTrDimensions() && nodeName( elem, "tr" ) || // Fall back to offsetWidth/offsetHeight when value is "auto" // This happens for inline elements with no explicit setting (gh-3571) val === "auto" || // Support: Android <=4.1 - 4.3 only // Also use offsetWidth/offsetHeight for misreported inline dimensions (gh-3602) !parseFloat( val ) && jQuery.css( elem, "display", false, styles ) === "inline" ) && // Make sure the element is visible & connected elem.getClientRects().length ) { isBorderBox = jQuery.css( elem, "boxSizing", false, styles ) === "border-box"; // Where available, offsetWidth/offsetHeight approximate border box dimensions. // Where not available (e.g., SVG), assume unreliable box-sizing and interpret the // retrieved value as a content box dimension. valueIsBorderBox = offsetProp in elem; if ( valueIsBorderBox ) { val = elem[ offsetProp ]; } } // Normalize "" and auto val = parseFloat( val ) || 0; // Adjust for the element's box model return ( val + boxModelAdjustment( elem, dimension, extra || ( isBorderBox ? "border" : "content" ), valueIsBorderBox, styles, // Provide the current computed size to request scroll gutter calculation (gh-3589) val ) ) + "px"; } jQuery.extend( { // Add in style property hooks for overriding the default // behavior of getting and setting a style property cssHooks: { opacity: { get: function( elem, computed ) { if ( computed ) { // We should always get a number back from opacity var ret = curCSS( elem, "opacity" ); return ret === "" ? "1" : ret; } } } }, // Don't automatically add "px" to these possibly-unitless properties cssNumber: { "animationIterationCount": true, "columnCount": true, "fillOpacity": true, "flexGrow": true, "flexShrink": true, "fontWeight": true, "gridArea": true, "gridColumn": true, "gridColumnEnd": true, "gridColumnStart": true, "gridRow": true, "gridRowEnd": true, "gridRowStart": true, "lineHeight": true, "opacity": true, "order": true, "orphans": true, "widows": true, "zIndex": true, "zoom": true }, // Add in properties whose names you wish to fix before // setting or getting the value cssProps: {}, // Get and set the style property on a DOM Node style: function( elem, name, value, extra ) { // Don't set styles on text and comment nodes if ( !elem || elem.nodeType === 3 || elem.nodeType === 8 || !elem.style ) { return; } // Make sure that we're working with the right name var ret, type, hooks, origName = camelCase( name ), isCustomProp = rcustomProp.test( name ), style = elem.style; // Make sure that we're working with the right name. We don't // want to query the value if it is a CSS custom property // since they are user-defined. if ( !isCustomProp ) { name = finalPropName( origName ); } // Gets hook for the prefixed version, then unprefixed version hooks = jQuery.cssHooks[ name ] || jQuery.cssHooks[ origName ]; // Check if we're setting a value if ( value !== undefined ) { type = typeof value; // Convert "+=" or "-=" to relative numbers (#7345) if ( type === "string" && ( ret = rcssNum.exec( value ) ) && ret[ 1 ] ) { value = adjustCSS( elem, name, ret ); // Fixes bug #9237 type = "number"; } // Make sure that null and NaN values aren't set (#7116) if ( value == null || value !== value ) { return; } // If a number was passed in, add the unit (except for certain CSS properties) // The isCustomProp check can be removed in jQuery 4.0 when we only auto-append // "px" to a few hardcoded values. if ( type === "number" && !isCustomProp ) { value += ret && ret[ 3 ] || ( jQuery.cssNumber[ origName ] ? "" : "px" ); } // background-* props affect original clone's values if ( !support.clearCloneStyle && value === "" && name.indexOf( "background" ) === 0 ) { style[ name ] = "inherit"; } // If a hook was provided, use that value, otherwise just set the specified value if ( !hooks || !( "set" in hooks ) || ( value = hooks.set( elem, value, extra ) ) !== undefined ) { if ( isCustomProp ) { style.setProperty( name, value ); } else { style[ name ] = value; } } } else { // If a hook was provided get the non-computed value from there if ( hooks && "get" in hooks && ( ret = hooks.get( elem, false, extra ) ) !== undefined ) { return ret; } // Otherwise just get the value from the style object return style[ name ]; } }, css: function( elem, name, extra, styles ) { var val, num, hooks, origName = camelCase( name ), isCustomProp = rcustomProp.test( name ); // Make sure that we're working with the right name. We don't // want to modify the value if it is a CSS custom property // since they are user-defined. if ( !isCustomProp ) { name = finalPropName( origName ); } // Try prefixed name followed by the unprefixed name hooks = jQuery.cssHooks[ name ] || jQuery.cssHooks[ origName ]; // If a hook was provided get the computed value from there if ( hooks && "get" in hooks ) { val = hooks.get( elem, true, extra ); } // Otherwise, if a way to get the computed value exists, use that if ( val === undefined ) { val = curCSS( elem, name, styles ); } // Convert "normal" to computed value if ( val === "normal" && name in cssNormalTransform ) { val = cssNormalTransform[ name ]; } // Make numeric if forced or a qualifier was provided and val looks numeric if ( extra === "" || extra ) { num = parseFloat( val ); return extra === true || isFinite( num ) ? num || 0 : val; } return val; } } ); jQuery.each( [ "height", "width" ], function( _i, dimension ) { jQuery.cssHooks[ dimension ] = { get: function( elem, computed, extra ) { if ( computed ) { // Certain elements can have dimension info if we invisibly show them // but it must have a current display style that would benefit return rdisplayswap.test( jQuery.css( elem, "display" ) ) && // Support: Safari 8+ // Table columns in Safari have non-zero offsetWidth & zero // getBoundingClientRect().width unless display is changed. // Support: IE <=11 only // Running getBoundingClientRect on a disconnected node // in IE throws an error. ( !elem.getClientRects().length || !elem.getBoundingClientRect().width ) ? swap( elem, cssShow, function() { return getWidthOrHeight( elem, dimension, extra ); } ) : getWidthOrHeight( elem, dimension, extra ); } }, set: function( elem, value, extra ) { var matches, styles = getStyles( elem ), // Only read styles.position if the test has a chance to fail // to avoid forcing a reflow. scrollboxSizeBuggy = !support.scrollboxSize() && styles.position === "absolute", // To avoid forcing a reflow, only fetch boxSizing if we need it (gh-3991) boxSizingNeeded = scrollboxSizeBuggy || extra, isBorderBox = boxSizingNeeded && jQuery.css( elem, "boxSizing", false, styles ) === "border-box", subtract = extra ? boxModelAdjustment( elem, dimension, extra, isBorderBox, styles ) : 0; // Account for unreliable border-box dimensions by comparing offset* to computed and // faking a content-box to get border and padding (gh-3699) if ( isBorderBox && scrollboxSizeBuggy ) { subtract -= Math.ceil( elem[ "offset" + dimension[ 0 ].toUpperCase() + dimension.slice( 1 ) ] - parseFloat( styles[ dimension ] ) - boxModelAdjustment( elem, dimension, "border", false, styles ) - 0.5 ); } // Convert to pixels if value adjustment is needed if ( subtract && ( matches = rcssNum.exec( value ) ) && ( matches[ 3 ] || "px" ) !== "px" ) { elem.style[ dimension ] = value; value = jQuery.css( elem, dimension ); } return setPositiveNumber( elem, value, subtract ); } }; } ); jQuery.cssHooks.marginLeft = addGetHookIf( support.reliableMarginLeft, function( elem, computed ) { if ( computed ) { return ( parseFloat( curCSS( elem, "marginLeft" ) ) || elem.getBoundingClientRect().left - swap( elem, { marginLeft: 0 }, function() { return elem.getBoundingClientRect().left; } ) ) + "px"; } } ); // These hooks are used by animate to expand properties jQuery.each( { margin: "", padding: "", border: "Width" }, function( prefix, suffix ) { jQuery.cssHooks[ prefix + suffix ] = { expand: function( value ) { var i = 0, expanded = {}, // Assumes a single number if not a string parts = typeof value === "string" ? value.split( " " ) : [ value ]; for ( ; i < 4; i++ ) { expanded[ prefix + cssExpand[ i ] + suffix ] = parts[ i ] || parts[ i - 2 ] || parts[ 0 ]; } return expanded; } }; if ( prefix !== "margin" ) { jQuery.cssHooks[ prefix + suffix ].set = setPositiveNumber; } } ); jQuery.fn.extend( { css: function( name, value ) { return access( this, function( elem, name, value ) { var styles, len, map = {}, i = 0; if ( Array.isArray( name ) ) { styles = getStyles( elem ); len = name.length; for ( ; i < len; i++ ) { map[ name[ i ] ] = jQuery.css( elem, name[ i ], false, styles ); } return map; } return value !== undefined ? jQuery.style( elem, name, value ) : jQuery.css( elem, name ); }, name, value, arguments.length > 1 ); } } ); function Tween( elem, options, prop, end, easing ) { return new Tween.prototype.init( elem, options, prop, end, easing ); } jQuery.Tween = Tween; Tween.prototype = { constructor: Tween, init: function( elem, options, prop, end, easing, unit ) { this.elem = elem; this.prop = prop; this.easing = easing || jQuery.easing._default; this.options = options; this.start = this.now = this.cur(); this.end = end; this.unit = unit || ( jQuery.cssNumber[ prop ] ? "" : "px" ); }, cur: function() { var hooks = Tween.propHooks[ this.prop ]; return hooks && hooks.get ? hooks.get( this ) : Tween.propHooks._default.get( this ); }, run: function( percent ) { var eased, hooks = Tween.propHooks[ this.prop ]; if ( this.options.duration ) { this.pos = eased = jQuery.easing[ this.easing ]( percent, this.options.duration * percent, 0, 1, this.options.duration ); } else { this.pos = eased = percent; } this.now = ( this.end - this.start ) * eased + this.start; if ( this.options.step ) { this.options.step.call( this.elem, this.now, this ); } if ( hooks && hooks.set ) { hooks.set( this ); } else { Tween.propHooks._default.set( this ); } return this; } }; Tween.prototype.init.prototype = Tween.prototype; Tween.propHooks = { _default: { get: function( tween ) { var result; // Use a property on the element directly when it is not a DOM element, // or when there is no matching style property that exists. if ( tween.elem.nodeType !== 1 || tween.elem[ tween.prop ] != null && tween.elem.style[ tween.prop ] == null ) { return tween.elem[ tween.prop ]; } // Passing an empty string as a 3rd parameter to .css will automatically // attempt a parseFloat and fallback to a string if the parse fails. // Simple values such as "10px" are parsed to Float; // complex values such as "rotate(1rad)" are returned as-is. result = jQuery.css( tween.elem, tween.prop, "" ); // Empty strings, null, undefined and "auto" are converted to 0. return !result || result === "auto" ? 0 : result; }, set: function( tween ) { // Use step hook for back compat. // Use cssHook if its there. // Use .style if available and use plain properties where available. if ( jQuery.fx.step[ tween.prop ] ) { jQuery.fx.step[ tween.prop ]( tween ); } else if ( tween.elem.nodeType === 1 && ( jQuery.cssHooks[ tween.prop ] || tween.elem.style[ finalPropName( tween.prop ) ] != null ) ) { jQuery.style( tween.elem, tween.prop, tween.now + tween.unit ); } else { tween.elem[ tween.prop ] = tween.now; } } } }; // Support: IE <=9 only // Panic based approach to setting things on disconnected nodes Tween.propHooks.scrollTop = Tween.propHooks.scrollLeft = { set: function( tween ) { if ( tween.elem.nodeType && tween.elem.parentNode ) { tween.elem[ tween.prop ] = tween.now; } } }; jQuery.easing = { linear: function( p ) { return p; }, swing: function( p ) { return 0.5 - Math.cos( p * Math.PI ) / 2; }, _default: "swing" }; jQuery.fx = Tween.prototype.init; // Back compat <1.8 extension point jQuery.fx.step = {}; var fxNow, inProgress, rfxtypes = /^(?:toggle|show|hide)$/, rrun = /queueHooks$/; function schedule() { if ( inProgress ) { if ( document.hidden === false && window.requestAnimationFrame ) { window.requestAnimationFrame( schedule ); } else { window.setTimeout( schedule, jQuery.fx.interval ); } jQuery.fx.tick(); } } // Animations created synchronously will run synchronously function createFxNow() { window.setTimeout( function() { fxNow = undefined; } ); return ( fxNow = Date.now() ); } // Generate parameters to create a standard animation function genFx( type, includeWidth ) { var which, i = 0, attrs = { height: type }; // If we include width, step value is 1 to do all cssExpand values, // otherwise step value is 2 to skip over Left and Right includeWidth = includeWidth ? 1 : 0; for ( ; i < 4; i += 2 - includeWidth ) { which = cssExpand[ i ]; attrs[ "margin" + which ] = attrs[ "padding" + which ] = type; } if ( includeWidth ) { attrs.opacity = attrs.width = type; } return attrs; } function createTween( value, prop, animation ) { var tween, collection = ( Animation.tweeners[ prop ] || [] ).concat( Animation.tweeners[ "*" ] ), index = 0, length = collection.length; for ( ; index < length; index++ ) { if ( ( tween = collection[ index ].call( animation, prop, value ) ) ) { // We're done with this property return tween; } } } function defaultPrefilter( elem, props, opts ) { var prop, value, toggle, hooks, oldfire, propTween, restoreDisplay, display, isBox = "width" in props || "height" in props, anim = this, orig = {}, style = elem.style, hidden = elem.nodeType && isHiddenWithinTree( elem ), dataShow = dataPriv.get( elem, "fxshow" ); // Queue-skipping animations hijack the fx hooks if ( !opts.queue ) { hooks = jQuery._queueHooks( elem, "fx" ); if ( hooks.unqueued == null ) { hooks.unqueued = 0; oldfire = hooks.empty.fire; hooks.empty.fire = function() { if ( !hooks.unqueued ) { oldfire(); } }; } hooks.unqueued++; anim.always( function() { // Ensure the complete handler is called before this completes anim.always( function() { hooks.unqueued--; if ( !jQuery.queue( elem, "fx" ).length ) { hooks.empty.fire(); } } ); } ); } // Detect show/hide animations for ( prop in props ) { value = props[ prop ]; if ( rfxtypes.test( value ) ) { delete props[ prop ]; toggle = toggle || value === "toggle"; if ( value === ( hidden ? "hide" : "show" ) ) { // Pretend to be hidden if this is a "show" and // there is still data from a stopped show/hide if ( value === "show" && dataShow && dataShow[ prop ] !== undefined ) { hidden = true; // Ignore all other no-op show/hide data } else { continue; } } orig[ prop ] = dataShow && dataShow[ prop ] || jQuery.style( elem, prop ); } } // Bail out if this is a no-op like .hide().hide() propTween = !jQuery.isEmptyObject( props ); if ( !propTween && jQuery.isEmptyObject( orig ) ) { return; } // Restrict "overflow" and "display" styles during box animations if ( isBox && elem.nodeType === 1 ) { // Support: IE <=9 - 11, Edge 12 - 15 // Record all 3 overflow attributes because IE does not infer the shorthand // from identically-valued overflowX and overflowY and Edge just mirrors // the overflowX value there. opts.overflow = [ style.overflow, style.overflowX, style.overflowY ]; // Identify a display type, preferring old show/hide data over the CSS cascade restoreDisplay = dataShow && dataShow.display; if ( restoreDisplay == null ) { restoreDisplay = dataPriv.get( elem, "display" ); } display = jQuery.css( elem, "display" ); if ( display === "none" ) { if ( restoreDisplay ) { display = restoreDisplay; } else { // Get nonempty value(s) by temporarily forcing visibility showHide( [ elem ], true ); restoreDisplay = elem.style.display || restoreDisplay; display = jQuery.css( elem, "display" ); showHide( [ elem ] ); } } // Animate inline elements as inline-block if ( display === "inline" || display === "inline-block" && restoreDisplay != null ) { if ( jQuery.css( elem, "float" ) === "none" ) { // Restore the original display value at the end of pure show/hide animations if ( !propTween ) { anim.done( function() { style.display = restoreDisplay; } ); if ( restoreDisplay == null ) { display = style.display; restoreDisplay = display === "none" ? "" : display; } } style.display = "inline-block"; } } } if ( opts.overflow ) { style.overflow = "hidden"; anim.always( function() { style.overflow = opts.overflow[ 0 ]; style.overflowX = opts.overflow[ 1 ]; style.overflowY = opts.overflow[ 2 ]; } ); } // Implement show/hide animations propTween = false; for ( prop in orig ) { // General show/hide setup for this element animation if ( !propTween ) { if ( dataShow ) { if ( "hidden" in dataShow ) { hidden = dataShow.hidden; } } else { dataShow = dataPriv.access( elem, "fxshow", { display: restoreDisplay } ); } // Store hidden/visible for toggle so `.stop().toggle()` "reverses" if ( toggle ) { dataShow.hidden = !hidden; } // Show elements before animating them if ( hidden ) { showHide( [ elem ], true ); } /* eslint-disable no-loop-func */ anim.done( function() { /* eslint-enable no-loop-func */ // The final step of a "hide" animation is actually hiding the element if ( !hidden ) { showHide( [ elem ] ); } dataPriv.remove( elem, "fxshow" ); for ( prop in orig ) { jQuery.style( elem, prop, orig[ prop ] ); } } ); } // Per-property setup propTween = createTween( hidden ? dataShow[ prop ] : 0, prop, anim ); if ( !( prop in dataShow ) ) { dataShow[ prop ] = propTween.start; if ( hidden ) { propTween.end = propTween.start; propTween.start = 0; } } } } function propFilter( props, specialEasing ) { var index, name, easing, value, hooks; // camelCase, specialEasing and expand cssHook pass for ( index in props ) { name = camelCase( index ); easing = specialEasing[ name ]; value = props[ index ]; if ( Array.isArray( value ) ) { easing = value[ 1 ]; value = props[ index ] = value[ 0 ]; } if ( index !== name ) { props[ name ] = value; delete props[ index ]; } hooks = jQuery.cssHooks[ name ]; if ( hooks && "expand" in hooks ) { value = hooks.expand( value ); delete props[ name ]; // Not quite $.extend, this won't overwrite existing keys. // Reusing 'index' because we have the correct "name" for ( index in value ) { if ( !( index in props ) ) { props[ index ] = value[ index ]; specialEasing[ index ] = easing; } } } else { specialEasing[ name ] = easing; } } } function Animation( elem, properties, options ) { var result, stopped, index = 0, length = Animation.prefilters.length, deferred = jQuery.Deferred().always( function() { // Don't match elem in the :animated selector delete tick.elem; } ), tick = function() { if ( stopped ) { return false; } var currentTime = fxNow || createFxNow(), remaining = Math.max( 0, animation.startTime + animation.duration - currentTime ), // Support: Android 2.3 only // Archaic crash bug won't allow us to use `1 - ( 0.5 || 0 )` (#12497) temp = remaining / animation.duration || 0, percent = 1 - temp, index = 0, length = animation.tweens.length; for ( ; index < length; index++ ) { animation.tweens[ index ].run( percent ); } deferred.notifyWith( elem, [ animation, percent, remaining ] ); // If there's more to do, yield if ( percent < 1 && length ) { return remaining; } // If this was an empty animation, synthesize a final progress notification if ( !length ) { deferred.notifyWith( elem, [ animation, 1, 0 ] ); } // Resolve the animation and report its conclusion deferred.resolveWith( elem, [ animation ] ); return false; }, animation = deferred.promise( { elem: elem, props: jQuery.extend( {}, properties ), opts: jQuery.extend( true, { specialEasing: {}, easing: jQuery.easing._default }, options ), originalProperties: properties, originalOptions: options, startTime: fxNow || createFxNow(), duration: options.duration, tweens: [], createTween: function( prop, end ) { var tween = jQuery.Tween( elem, animation.opts, prop, end, animation.opts.specialEasing[ prop ] || animation.opts.easing ); animation.tweens.push( tween ); return tween; }, stop: function( gotoEnd ) { var index = 0, // If we are going to the end, we want to run all the tweens // otherwise we skip this part length = gotoEnd ? animation.tweens.length : 0; if ( stopped ) { return this; } stopped = true; for ( ; index < length; index++ ) { animation.tweens[ index ].run( 1 ); } // Resolve when we played the last frame; otherwise, reject if ( gotoEnd ) { deferred.notifyWith( elem, [ animation, 1, 0 ] ); deferred.resolveWith( elem, [ animation, gotoEnd ] ); } else { deferred.rejectWith( elem, [ animation, gotoEnd ] ); } return this; } } ), props = animation.props; propFilter( props, animation.opts.specialEasing ); for ( ; index < length; index++ ) { result = Animation.prefilters[ index ].call( animation, elem, props, animation.opts ); if ( result ) { if ( isFunction( result.stop ) ) { jQuery._queueHooks( animation.elem, animation.opts.queue ).stop = result.stop.bind( result ); } return result; } } jQuery.map( props, createTween, animation ); if ( isFunction( animation.opts.start ) ) { animation.opts.start.call( elem, animation ); } // Attach callbacks from options animation .progress( animation.opts.progress ) .done( animation.opts.done, animation.opts.complete ) .fail( animation.opts.fail ) .always( animation.opts.always ); jQuery.fx.timer( jQuery.extend( tick, { elem: elem, anim: animation, queue: animation.opts.queue } ) ); return animation; } jQuery.Animation = jQuery.extend( Animation, { tweeners: { "*": [ function( prop, value ) { var tween = this.createTween( prop, value ); adjustCSS( tween.elem, prop, rcssNum.exec( value ), tween ); return tween; } ] }, tweener: function( props, callback ) { if ( isFunction( props ) ) { callback = props; props = [ "*" ]; } else { props = props.match( rnothtmlwhite ); } var prop, index = 0, length = props.length; for ( ; index < length; index++ ) { prop = props[ index ]; Animation.tweeners[ prop ] = Animation.tweeners[ prop ] || []; Animation.tweeners[ prop ].unshift( callback ); } }, prefilters: [ defaultPrefilter ], prefilter: function( callback, prepend ) { if ( prepend ) { Animation.prefilters.unshift( callback ); } else { Animation.prefilters.push( callback ); } } } ); jQuery.speed = function( speed, easing, fn ) { var opt = speed && typeof speed === "object" ? jQuery.extend( {}, speed ) : { complete: fn || !fn && easing || isFunction( speed ) && speed, duration: speed, easing: fn && easing || easing && !isFunction( easing ) && easing }; // Go to the end state if fx are off if ( jQuery.fx.off ) { opt.duration = 0; } else { if ( typeof opt.duration !== "number" ) { if ( opt.duration in jQuery.fx.speeds ) { opt.duration = jQuery.fx.speeds[ opt.duration ]; } else { opt.duration = jQuery.fx.speeds._default; } } } // Normalize opt.queue - true/undefined/null -> "fx" if ( opt.queue == null || opt.queue === true ) { opt.queue = "fx"; } // Queueing opt.old = opt.complete; opt.complete = function() { if ( isFunction( opt.old ) ) { opt.old.call( this ); } if ( opt.queue ) { jQuery.dequeue( this, opt.queue ); } }; return opt; }; jQuery.fn.extend( { fadeTo: function( speed, to, easing, callback ) { // Show any hidden elements after setting opacity to 0 return this.filter( isHiddenWithinTree ).css( "opacity", 0 ).show() // Animate to the value specified .end().animate( { opacity: to }, speed, easing, callback ); }, animate: function( prop, speed, easing, callback ) { var empty = jQuery.isEmptyObject( prop ), optall = jQuery.speed( speed, easing, callback ), doAnimation = function() { // Operate on a copy of prop so per-property easing won't be lost var anim = Animation( this, jQuery.extend( {}, prop ), optall ); // Empty animations, or finishing resolves immediately if ( empty || dataPriv.get( this, "finish" ) ) { anim.stop( true ); } }; doAnimation.finish = doAnimation; return empty || optall.queue === false ? this.each( doAnimation ) : this.queue( optall.queue, doAnimation ); }, stop: function( type, clearQueue, gotoEnd ) { var stopQueue = function( hooks ) { var stop = hooks.stop; delete hooks.stop; stop( gotoEnd ); }; if ( typeof type !== "string" ) { gotoEnd = clearQueue; clearQueue = type; type = undefined; } if ( clearQueue ) { this.queue( type || "fx", [] ); } return this.each( function() { var dequeue = true, index = type != null && type + "queueHooks", timers = jQuery.timers, data = dataPriv.get( this ); if ( index ) { if ( data[ index ] && data[ index ].stop ) { stopQueue( data[ index ] ); } } else { for ( index in data ) { if ( data[ index ] && data[ index ].stop && rrun.test( index ) ) { stopQueue( data[ index ] ); } } } for ( index = timers.length; index--; ) { if ( timers[ index ].elem === this && ( type == null || timers[ index ].queue === type ) ) { timers[ index ].anim.stop( gotoEnd ); dequeue = false; timers.splice( index, 1 ); } } // Start the next in the queue if the last step wasn't forced. // Timers currently will call their complete callbacks, which // will dequeue but only if they were gotoEnd. if ( dequeue || !gotoEnd ) { jQuery.dequeue( this, type ); } } ); }, finish: function( type ) { if ( type !== false ) { type = type || "fx"; } return this.each( function() { var index, data = dataPriv.get( this ), queue = data[ type + "queue" ], hooks = data[ type + "queueHooks" ], timers = jQuery.timers, length = queue ? queue.length : 0; // Enable finishing flag on private data data.finish = true; // Empty the queue first jQuery.queue( this, type, [] ); if ( hooks && hooks.stop ) { hooks.stop.call( this, true ); } // Look for any active animations, and finish them for ( index = timers.length; index--; ) { if ( timers[ index ].elem === this && timers[ index ].queue === type ) { timers[ index ].anim.stop( true ); timers.splice( index, 1 ); } } // Look for any animations in the old queue and finish them for ( index = 0; index < length; index++ ) { if ( queue[ index ] && queue[ index ].finish ) { queue[ index ].finish.call( this ); } } // Turn off finishing flag delete data.finish; } ); } } ); jQuery.each( [ "toggle", "show", "hide" ], function( _i, name ) { var cssFn = jQuery.fn[ name ]; jQuery.fn[ name ] = function( speed, easing, callback ) { return speed == null || typeof speed === "boolean" ? cssFn.apply( this, arguments ) : this.animate( genFx( name, true ), speed, easing, callback ); }; } ); // Generate shortcuts for custom animations jQuery.each( { slideDown: genFx( "show" ), slideUp: genFx( "hide" ), slideToggle: genFx( "toggle" ), fadeIn: { opacity: "show" }, fadeOut: { opacity: "hide" }, fadeToggle: { opacity: "toggle" } }, function( name, props ) { jQuery.fn[ name ] = function( speed, easing, callback ) { return this.animate( props, speed, easing, callback ); }; } ); jQuery.timers = []; jQuery.fx.tick = function() { var timer, i = 0, timers = jQuery.timers; fxNow = Date.now(); for ( ; i < timers.length; i++ ) { timer = timers[ i ]; // Run the timer and safely remove it when done (allowing for external removal) if ( !timer() && timers[ i ] === timer ) { timers.splice( i--, 1 ); } } if ( !timers.length ) { jQuery.fx.stop(); } fxNow = undefined; }; jQuery.fx.timer = function( timer ) { jQuery.timers.push( timer ); jQuery.fx.start(); }; jQuery.fx.interval = 13; jQuery.fx.start = function() { if ( inProgress ) { return; } inProgress = true; schedule(); }; jQuery.fx.stop = function() { inProgress = null; }; jQuery.fx.speeds = { slow: 600, fast: 200, // Default speed _default: 400 }; // Based off of the plugin by Clint Helfers, with permission. // https://web.archive.org/web/20100324014747/http://blindsignals.com/index.php/2009/07/jquery-delay/ jQuery.fn.delay = function( time, type ) { time = jQuery.fx ? jQuery.fx.speeds[ time ] || time : time; type = type || "fx"; return this.queue( type, function( next, hooks ) { var timeout = window.setTimeout( next, time ); hooks.stop = function() { window.clearTimeout( timeout ); }; } ); }; ( function() { var input = document.createElement( "input" ), select = document.createElement( "select" ), opt = select.appendChild( document.createElement( "option" ) ); input.type = "checkbox"; // Support: Android <=4.3 only // Default value for a checkbox should be "on" support.checkOn = input.value !== ""; // Support: IE <=11 only // Must access selectedIndex to make default options select support.optSelected = opt.selected; // Support: IE <=11 only // An input loses its value after becoming a radio input = document.createElement( "input" ); input.value = "t"; input.type = "radio"; support.radioValue = input.value === "t"; } )(); var boolHook, attrHandle = jQuery.expr.attrHandle; jQuery.fn.extend( { attr: function( name, value ) { return access( this, jQuery.attr, name, value, arguments.length > 1 ); }, removeAttr: function( name ) { return this.each( function() { jQuery.removeAttr( this, name ); } ); } } ); jQuery.extend( { attr: function( elem, name, value ) { var ret, hooks, nType = elem.nodeType; // Don't get/set attributes on text, comment and attribute nodes if ( nType === 3 || nType === 8 || nType === 2 ) { return; } // Fallback to prop when attributes are not supported if ( typeof elem.getAttribute === "undefined" ) { return jQuery.prop( elem, name, value ); } // Attribute hooks are determined by the lowercase version // Grab necessary hook if one is defined if ( nType !== 1 || !jQuery.isXMLDoc( elem ) ) { hooks = jQuery.attrHooks[ name.toLowerCase() ] || ( jQuery.expr.match.bool.test( name ) ? boolHook : undefined ); } if ( value !== undefined ) { if ( value === null ) { jQuery.removeAttr( elem, name ); return; } if ( hooks && "set" in hooks && ( ret = hooks.set( elem, value, name ) ) !== undefined ) { return ret; } elem.setAttribute( name, value + "" ); return value; } if ( hooks && "get" in hooks && ( ret = hooks.get( elem, name ) ) !== null ) { return ret; } ret = jQuery.find.attr( elem, name ); // Non-existent attributes return null, we normalize to undefined return ret == null ? undefined : ret; }, attrHooks: { type: { set: function( elem, value ) { if ( !support.radioValue && value === "radio" && nodeName( elem, "input" ) ) { var val = elem.value; elem.setAttribute( "type", value ); if ( val ) { elem.value = val; } return value; } } } }, removeAttr: function( elem, value ) { var name, i = 0, // Attribute names can contain non-HTML whitespace characters // https://html.spec.whatwg.org/multipage/syntax.html#attributes-2 attrNames = value && value.match( rnothtmlwhite ); if ( attrNames && elem.nodeType === 1 ) { while ( ( name = attrNames[ i++ ] ) ) { elem.removeAttribute( name ); } } } } ); // Hooks for boolean attributes boolHook = { set: function( elem, value, name ) { if ( value === false ) { // Remove boolean attributes when set to false jQuery.removeAttr( elem, name ); } else { elem.setAttribute( name, name ); } return name; } }; jQuery.each( jQuery.expr.match.bool.source.match( /\w+/g ), function( _i, name ) { var getter = attrHandle[ name ] || jQuery.find.attr; attrHandle[ name ] = function( elem, name, isXML ) { var ret, handle, lowercaseName = name.toLowerCase(); if ( !isXML ) { // Avoid an infinite loop by temporarily removing this function from the getter handle = attrHandle[ lowercaseName ]; attrHandle[ lowercaseName ] = ret; ret = getter( elem, name, isXML ) != null ? lowercaseName : null; attrHandle[ lowercaseName ] = handle; } return ret; }; } ); var rfocusable = /^(?:input|select|textarea|button)$/i, rclickable = /^(?:a|area)$/i; jQuery.fn.extend( { prop: function( name, value ) { return access( this, jQuery.prop, name, value, arguments.length > 1 ); }, removeProp: function( name ) { return this.each( function() { delete this[ jQuery.propFix[ name ] || name ]; } ); } } ); jQuery.extend( { prop: function( elem, name, value ) { var ret, hooks, nType = elem.nodeType; // Don't get/set properties on text, comment and attribute nodes if ( nType === 3 || nType === 8 || nType === 2 ) { return; } if ( nType !== 1 || !jQuery.isXMLDoc( elem ) ) { // Fix name and attach hooks name = jQuery.propFix[ name ] || name; hooks = jQuery.propHooks[ name ]; } if ( value !== undefined ) { if ( hooks && "set" in hooks && ( ret = hooks.set( elem, value, name ) ) !== undefined ) { return ret; } return ( elem[ name ] = value ); } if ( hooks && "get" in hooks && ( ret = hooks.get( elem, name ) ) !== null ) { return ret; } return elem[ name ]; }, propHooks: { tabIndex: { get: function( elem ) { // Support: IE <=9 - 11 only // elem.tabIndex doesn't always return the // correct value when it hasn't been explicitly set // https://web.archive.org/web/20141116233347/http://fluidproject.org/blog/2008/01/09/getting-setting-and-removing-tabindex-values-with-javascript/ // Use proper attribute retrieval(#12072) var tabindex = jQuery.find.attr( elem, "tabindex" ); if ( tabindex ) { return parseInt( tabindex, 10 ); } if ( rfocusable.test( elem.nodeName ) || rclickable.test( elem.nodeName ) && elem.href ) { return 0; } return -1; } } }, propFix: { "for": "htmlFor", "class": "className" } } ); // Support: IE <=11 only // Accessing the selectedIndex property // forces the browser to respect setting selected // on the option // The getter ensures a default option is selected // when in an optgroup // eslint rule "no-unused-expressions" is disabled for this code // since it considers such accessions noop if ( !support.optSelected ) { jQuery.propHooks.selected = { get: function( elem ) { /* eslint no-unused-expressions: "off" */ var parent = elem.parentNode; if ( parent && parent.parentNode ) { parent.parentNode.selectedIndex; } return null; }, set: function( elem ) { /* eslint no-unused-expressions: "off" */ var parent = elem.parentNode; if ( parent ) { parent.selectedIndex; if ( parent.parentNode ) { parent.parentNode.selectedIndex; } } } }; } jQuery.each( [ "tabIndex", "readOnly", "maxLength", "cellSpacing", "cellPadding", "rowSpan", "colSpan", "useMap", "frameBorder", "contentEditable" ], function() { jQuery.propFix[ this.toLowerCase() ] = this; } ); // Strip and collapse whitespace according to HTML spec // https://infra.spec.whatwg.org/#strip-and-collapse-ascii-whitespace function stripAndCollapse( value ) { var tokens = value.match( rnothtmlwhite ) || []; return tokens.join( " " ); } function getClass( elem ) { return elem.getAttribute && elem.getAttribute( "class" ) || ""; } function classesToArray( value ) { if ( Array.isArray( value ) ) { return value; } if ( typeof value === "string" ) { return value.match( rnothtmlwhite ) || []; } return []; } jQuery.fn.extend( { addClass: function( value ) { var classes, elem, cur, curValue, clazz, j, finalValue, i = 0; if ( isFunction( value ) ) { return this.each( function( j ) { jQuery( this ).addClass( value.call( this, j, getClass( this ) ) ); } ); } classes = classesToArray( value ); if ( classes.length ) { while ( ( elem = this[ i++ ] ) ) { curValue = getClass( elem ); cur = elem.nodeType === 1 && ( " " + stripAndCollapse( curValue ) + " " ); if ( cur ) { j = 0; while ( ( clazz = classes[ j++ ] ) ) { if ( cur.indexOf( " " + clazz + " " ) < 0 ) { cur += clazz + " "; } } // Only assign if different to avoid unneeded rendering. finalValue = stripAndCollapse( cur ); if ( curValue !== finalValue ) { elem.setAttribute( "class", finalValue ); } } } } return this; }, removeClass: function( value ) { var classes, elem, cur, curValue, clazz, j, finalValue, i = 0; if ( isFunction( value ) ) { return this.each( function( j ) { jQuery( this ).removeClass( value.call( this, j, getClass( this ) ) ); } ); } if ( !arguments.length ) { return this.attr( "class", "" ); } classes = classesToArray( value ); if ( classes.length ) { while ( ( elem = this[ i++ ] ) ) { curValue = getClass( elem ); // This expression is here for better compressibility (see addClass) cur = elem.nodeType === 1 && ( " " + stripAndCollapse( curValue ) + " " ); if ( cur ) { j = 0; while ( ( clazz = classes[ j++ ] ) ) { // Remove *all* instances while ( cur.indexOf( " " + clazz + " " ) > -1 ) { cur = cur.replace( " " + clazz + " ", " " ); } } // Only assign if different to avoid unneeded rendering. finalValue = stripAndCollapse( cur ); if ( curValue !== finalValue ) { elem.setAttribute( "class", finalValue ); } } } } return this; }, toggleClass: function( value, stateVal ) { var type = typeof value, isValidValue = type === "string" || Array.isArray( value ); if ( typeof stateVal === "boolean" && isValidValue ) { return stateVal ? this.addClass( value ) : this.removeClass( value ); } if ( isFunction( value ) ) { return this.each( function( i ) { jQuery( this ).toggleClass( value.call( this, i, getClass( this ), stateVal ), stateVal ); } ); } return this.each( function() { var className, i, self, classNames; if ( isValidValue ) { // Toggle individual class names i = 0; self = jQuery( this ); classNames = classesToArray( value ); while ( ( className = classNames[ i++ ] ) ) { // Check each className given, space separated list if ( self.hasClass( className ) ) { self.removeClass( className ); } else { self.addClass( className ); } } // Toggle whole class name } else if ( value === undefined || type === "boolean" ) { className = getClass( this ); if ( className ) { // Store className if set dataPriv.set( this, "__className__", className ); } // If the element has a class name or if we're passed `false`, // then remove the whole classname (if there was one, the above saved it). // Otherwise bring back whatever was previously saved (if anything), // falling back to the empty string if nothing was stored. if ( this.setAttribute ) { this.setAttribute( "class", className || value === false ? "" : dataPriv.get( this, "__className__" ) || "" ); } } } ); }, hasClass: function( selector ) { var className, elem, i = 0; className = " " + selector + " "; while ( ( elem = this[ i++ ] ) ) { if ( elem.nodeType === 1 && ( " " + stripAndCollapse( getClass( elem ) ) + " " ).indexOf( className ) > -1 ) { return true; } } return false; } } ); var rreturn = /\r/g; jQuery.fn.extend( { val: function( value ) { var hooks, ret, valueIsFunction, elem = this[ 0 ]; if ( !arguments.length ) { if ( elem ) { hooks = jQuery.valHooks[ elem.type ] || jQuery.valHooks[ elem.nodeName.toLowerCase() ]; if ( hooks && "get" in hooks && ( ret = hooks.get( elem, "value" ) ) !== undefined ) { return ret; } ret = elem.value; // Handle most common string cases if ( typeof ret === "string" ) { return ret.replace( rreturn, "" ); } // Handle cases where value is null/undef or number return ret == null ? "" : ret; } return; } valueIsFunction = isFunction( value ); return this.each( function( i ) { var val; if ( this.nodeType !== 1 ) { return; } if ( valueIsFunction ) { val = value.call( this, i, jQuery( this ).val() ); } else { val = value; } // Treat null/undefined as ""; convert numbers to string if ( val == null ) { val = ""; } else if ( typeof val === "number" ) { val += ""; } else if ( Array.isArray( val ) ) { val = jQuery.map( val, function( value ) { return value == null ? "" : value + ""; } ); } hooks = jQuery.valHooks[ this.type ] || jQuery.valHooks[ this.nodeName.toLowerCase() ]; // If set returns undefined, fall back to normal setting if ( !hooks || !( "set" in hooks ) || hooks.set( this, val, "value" ) === undefined ) { this.value = val; } } ); } } ); jQuery.extend( { valHooks: { option: { get: function( elem ) { var val = jQuery.find.attr( elem, "value" ); return val != null ? val : // Support: IE <=10 - 11 only // option.text throws exceptions (#14686, #14858) // Strip and collapse whitespace // https://html.spec.whatwg.org/#strip-and-collapse-whitespace stripAndCollapse( jQuery.text( elem ) ); } }, select: { get: function( elem ) { var value, option, i, options = elem.options, index = elem.selectedIndex, one = elem.type === "select-one", values = one ? null : [], max = one ? index + 1 : options.length; if ( index < 0 ) { i = max; } else { i = one ? index : 0; } // Loop through all the selected options for ( ; i < max; i++ ) { option = options[ i ]; // Support: IE <=9 only // IE8-9 doesn't update selected after form reset (#2551) if ( ( option.selected || i === index ) && // Don't return options that are disabled or in a disabled optgroup !option.disabled && ( !option.parentNode.disabled || !nodeName( option.parentNode, "optgroup" ) ) ) { // Get the specific value for the option value = jQuery( option ).val(); // We don't need an array for one selects if ( one ) { return value; } // Multi-Selects return an array values.push( value ); } } return values; }, set: function( elem, value ) { var optionSet, option, options = elem.options, values = jQuery.makeArray( value ), i = options.length; while ( i-- ) { option = options[ i ]; /* eslint-disable no-cond-assign */ if ( option.selected = jQuery.inArray( jQuery.valHooks.option.get( option ), values ) > -1 ) { optionSet = true; } /* eslint-enable no-cond-assign */ } // Force browsers to behave consistently when non-matching value is set if ( !optionSet ) { elem.selectedIndex = -1; } return values; } } } } ); // Radios and checkboxes getter/setter jQuery.each( [ "radio", "checkbox" ], function() { jQuery.valHooks[ this ] = { set: function( elem, value ) { if ( Array.isArray( value ) ) { return ( elem.checked = jQuery.inArray( jQuery( elem ).val(), value ) > -1 ); } } }; if ( !support.checkOn ) { jQuery.valHooks[ this ].get = function( elem ) { return elem.getAttribute( "value" ) === null ? "on" : elem.value; }; } } ); // Return jQuery for attributes-only inclusion support.focusin = "onfocusin" in window; var rfocusMorph = /^(?:focusinfocus|focusoutblur)$/, stopPropagationCallback = function( e ) { e.stopPropagation(); }; jQuery.extend( jQuery.event, { trigger: function( event, data, elem, onlyHandlers ) { var i, cur, tmp, bubbleType, ontype, handle, special, lastElement, eventPath = [ elem || document ], type = hasOwn.call( event, "type" ) ? event.type : event, namespaces = hasOwn.call( event, "namespace" ) ? event.namespace.split( "." ) : []; cur = lastElement = tmp = elem = elem || document; // Don't do events on text and comment nodes if ( elem.nodeType === 3 || elem.nodeType === 8 ) { return; } // focus/blur morphs to focusin/out; ensure we're not firing them right now if ( rfocusMorph.test( type + jQuery.event.triggered ) ) { return; } if ( type.indexOf( "." ) > -1 ) { // Namespaced trigger; create a regexp to match event type in handle() namespaces = type.split( "." ); type = namespaces.shift(); namespaces.sort(); } ontype = type.indexOf( ":" ) < 0 && "on" + type; // Caller can pass in a jQuery.Event object, Object, or just an event type string event = event[ jQuery.expando ] ? event : new jQuery.Event( type, typeof event === "object" && event ); // Trigger bitmask: & 1 for native handlers; & 2 for jQuery (always true) event.isTrigger = onlyHandlers ? 2 : 3; event.namespace = namespaces.join( "." ); event.rnamespace = event.namespace ? new RegExp( "(^|\\.)" + namespaces.join( "\\.(?:.*\\.|)" ) + "(\\.|$)" ) : null; // Clean up the event in case it is being reused event.result = undefined; if ( !event.target ) { event.target = elem; } // Clone any incoming data and prepend the event, creating the handler arg list data = data == null ? [ event ] : jQuery.makeArray( data, [ event ] ); // Allow special events to draw outside the lines special = jQuery.event.special[ type ] || {}; if ( !onlyHandlers && special.trigger && special.trigger.apply( elem, data ) === false ) { return; } // Determine event propagation path in advance, per W3C events spec (#9951) // Bubble up to document, then to window; watch for a global ownerDocument var (#9724) if ( !onlyHandlers && !special.noBubble && !isWindow( elem ) ) { bubbleType = special.delegateType || type; if ( !rfocusMorph.test( bubbleType + type ) ) { cur = cur.parentNode; } for ( ; cur; cur = cur.parentNode ) { eventPath.push( cur ); tmp = cur; } // Only add window if we got to document (e.g., not plain obj or detached DOM) if ( tmp === ( elem.ownerDocument || document ) ) { eventPath.push( tmp.defaultView || tmp.parentWindow || window ); } } // Fire handlers on the event path i = 0; while ( ( cur = eventPath[ i++ ] ) && !event.isPropagationStopped() ) { lastElement = cur; event.type = i > 1 ? bubbleType : special.bindType || type; // jQuery handler handle = ( dataPriv.get( cur, "events" ) || Object.create( null ) )[ event.type ] && dataPriv.get( cur, "handle" ); if ( handle ) { handle.apply( cur, data ); } // Native handler handle = ontype && cur[ ontype ]; if ( handle && handle.apply && acceptData( cur ) ) { event.result = handle.apply( cur, data ); if ( event.result === false ) { event.preventDefault(); } } } event.type = type; // If nobody prevented the default action, do it now if ( !onlyHandlers && !event.isDefaultPrevented() ) { if ( ( !special._default || special._default.apply( eventPath.pop(), data ) === false ) && acceptData( elem ) ) { // Call a native DOM method on the target with the same name as the event. // Don't do default actions on window, that's where global variables be (#6170) if ( ontype && isFunction( elem[ type ] ) && !isWindow( elem ) ) { // Don't re-trigger an onFOO event when we call its FOO() method tmp = elem[ ontype ]; if ( tmp ) { elem[ ontype ] = null; } // Prevent re-triggering of the same event, since we already bubbled it above jQuery.event.triggered = type; if ( event.isPropagationStopped() ) { lastElement.addEventListener( type, stopPropagationCallback ); } elem[ type ](); if ( event.isPropagationStopped() ) { lastElement.removeEventListener( type, stopPropagationCallback ); } jQuery.event.triggered = undefined; if ( tmp ) { elem[ ontype ] = tmp; } } } } return event.result; }, // Piggyback on a donor event to simulate a different one // Used only for `focus(in | out)` events simulate: function( type, elem, event ) { var e = jQuery.extend( new jQuery.Event(), event, { type: type, isSimulated: true } ); jQuery.event.trigger( e, null, elem ); } } ); jQuery.fn.extend( { trigger: function( type, data ) { return this.each( function() { jQuery.event.trigger( type, data, this ); } ); }, triggerHandler: function( type, data ) { var elem = this[ 0 ]; if ( elem ) { return jQuery.event.trigger( type, data, elem, true ); } } } ); // Support: Firefox <=44 // Firefox doesn't have focus(in | out) events // Related ticket - https://bugzilla.mozilla.org/show_bug.cgi?id=687787 // // Support: Chrome <=48 - 49, Safari <=9.0 - 9.1 // focus(in | out) events fire after focus & blur events, // which is spec violation - http://www.w3.org/TR/DOM-Level-3-Events/#events-focusevent-event-order // Related ticket - https://bugs.chromium.org/p/chromium/issues/detail?id=449857 if ( !support.focusin ) { jQuery.each( { focus: "focusin", blur: "focusout" }, function( orig, fix ) { // Attach a single capturing handler on the document while someone wants focusin/focusout var handler = function( event ) { jQuery.event.simulate( fix, event.target, jQuery.event.fix( event ) ); }; jQuery.event.special[ fix ] = { setup: function() { // Handle: regular nodes (via `this.ownerDocument`), window // (via `this.document`) & document (via `this`). var doc = this.ownerDocument || this.document || this, attaches = dataPriv.access( doc, fix ); if ( !attaches ) { doc.addEventListener( orig, handler, true ); } dataPriv.access( doc, fix, ( attaches || 0 ) + 1 ); }, teardown: function() { var doc = this.ownerDocument || this.document || this, attaches = dataPriv.access( doc, fix ) - 1; if ( !attaches ) { doc.removeEventListener( orig, handler, true ); dataPriv.remove( doc, fix ); } else { dataPriv.access( doc, fix, attaches ); } } }; } ); } var location = window.location; var nonce = { guid: Date.now() }; var rquery = ( /\?/ ); // Cross-browser xml parsing jQuery.parseXML = function( data ) { var xml, parserErrorElem; if ( !data || typeof data !== "string" ) { return null; } // Support: IE 9 - 11 only // IE throws on parseFromString with invalid input. try { xml = ( new window.DOMParser() ).parseFromString( data, "text/xml" ); } catch ( e ) {} parserErrorElem = xml && xml.getElementsByTagName( "parsererror" )[ 0 ]; if ( !xml || parserErrorElem ) { jQuery.error( "Invalid XML: " + ( parserErrorElem ? jQuery.map( parserErrorElem.childNodes, function( el ) { return el.textContent; } ).join( "\n" ) : data ) ); } return xml; }; var rbracket = /\[\]$/, rCRLF = /\r?\n/g, rsubmitterTypes = /^(?:submit|button|image|reset|file)$/i, rsubmittable = /^(?:input|select|textarea|keygen)/i; function buildParams( prefix, obj, traditional, add ) { var name; if ( Array.isArray( obj ) ) { // Serialize array item. jQuery.each( obj, function( i, v ) { if ( traditional || rbracket.test( prefix ) ) { // Treat each array item as a scalar. add( prefix, v ); } else { // Item is non-scalar (array or object), encode its numeric index. buildParams( prefix + "[" + ( typeof v === "object" && v != null ? i : "" ) + "]", v, traditional, add ); } } ); } else if ( !traditional && toType( obj ) === "object" ) { // Serialize object item. for ( name in obj ) { buildParams( prefix + "[" + name + "]", obj[ name ], traditional, add ); } } else { // Serialize scalar item. add( prefix, obj ); } } // Serialize an array of form elements or a set of // key/values into a query string jQuery.param = function( a, traditional ) { var prefix, s = [], add = function( key, valueOrFunction ) { // If value is a function, invoke it and use its return value var value = isFunction( valueOrFunction ) ? valueOrFunction() : valueOrFunction; s[ s.length ] = encodeURIComponent( key ) + "=" + encodeURIComponent( value == null ? "" : value ); }; if ( a == null ) { return ""; } // If an array was passed in, assume that it is an array of form elements. if ( Array.isArray( a ) || ( a.jquery && !jQuery.isPlainObject( a ) ) ) { // Serialize the form elements jQuery.each( a, function() { add( this.name, this.value ); } ); } else { // If traditional, encode the "old" way (the way 1.3.2 or older // did it), otherwise encode params recursively. for ( prefix in a ) { buildParams( prefix, a[ prefix ], traditional, add ); } } // Return the resulting serialization return s.join( "&" ); }; jQuery.fn.extend( { serialize: function() { return jQuery.param( this.serializeArray() ); }, serializeArray: function() { return this.map( function() { // Can add propHook for "elements" to filter or add form elements var elements = jQuery.prop( this, "elements" ); return elements ? jQuery.makeArray( elements ) : this; } ).filter( function() { var type = this.type; // Use .is( ":disabled" ) so that fieldset[disabled] works return this.name && !jQuery( this ).is( ":disabled" ) && rsubmittable.test( this.nodeName ) && !rsubmitterTypes.test( type ) && ( this.checked || !rcheckableType.test( type ) ); } ).map( function( _i, elem ) { var val = jQuery( this ).val(); if ( val == null ) { return null; } if ( Array.isArray( val ) ) { return jQuery.map( val, function( val ) { return { name: elem.name, value: val.replace( rCRLF, "\r\n" ) }; } ); } return { name: elem.name, value: val.replace( rCRLF, "\r\n" ) }; } ).get(); } } ); var r20 = /%20/g, rhash = /#.*$/, rantiCache = /([?&])_=[^&]*/, rheaders = /^(.*?):[ \t]*([^\r\n]*)$/mg, // #7653, #8125, #8152: local protocol detection rlocalProtocol = /^(?:about|app|app-storage|.+-extension|file|res|widget):$/, rnoContent = /^(?:GET|HEAD)$/, rprotocol = /^\/\//, /* Prefilters * 1) They are useful to introduce custom dataTypes (see ajax/jsonp.js for an example) * 2) These are called: * - BEFORE asking for a transport * - AFTER param serialization (s.data is a string if s.processData is true) * 3) key is the dataType * 4) the catchall symbol "*" can be used * 5) execution will start with transport dataType and THEN continue down to "*" if needed */ prefilters = {}, /* Transports bindings * 1) key is the dataType * 2) the catchall symbol "*" can be used * 3) selection will start with transport dataType and THEN go to "*" if needed */ transports = {}, // Avoid comment-prolog char sequence (#10098); must appease lint and evade compression allTypes = "*/".concat( "*" ), // Anchor tag for parsing the document origin originAnchor = document.createElement( "a" ); originAnchor.href = location.href; // Base "constructor" for jQuery.ajaxPrefilter and jQuery.ajaxTransport function addToPrefiltersOrTransports( structure ) { // dataTypeExpression is optional and defaults to "*" return function( dataTypeExpression, func ) { if ( typeof dataTypeExpression !== "string" ) { func = dataTypeExpression; dataTypeExpression = "*"; } var dataType, i = 0, dataTypes = dataTypeExpression.toLowerCase().match( rnothtmlwhite ) || []; if ( isFunction( func ) ) { // For each dataType in the dataTypeExpression while ( ( dataType = dataTypes[ i++ ] ) ) { // Prepend if requested if ( dataType[ 0 ] === "+" ) { dataType = dataType.slice( 1 ) || "*"; ( structure[ dataType ] = structure[ dataType ] || [] ).unshift( func ); // Otherwise append } else { ( structure[ dataType ] = structure[ dataType ] || [] ).push( func ); } } } }; } // Base inspection function for prefilters and transports function inspectPrefiltersOrTransports( structure, options, originalOptions, jqXHR ) { var inspected = {}, seekingTransport = ( structure === transports ); function inspect( dataType ) { var selected; inspected[ dataType ] = true; jQuery.each( structure[ dataType ] || [], function( _, prefilterOrFactory ) { var dataTypeOrTransport = prefilterOrFactory( options, originalOptions, jqXHR ); if ( typeof dataTypeOrTransport === "string" && !seekingTransport && !inspected[ dataTypeOrTransport ] ) { options.dataTypes.unshift( dataTypeOrTransport ); inspect( dataTypeOrTransport ); return false; } else if ( seekingTransport ) { return !( selected = dataTypeOrTransport ); } } ); return selected; } return inspect( options.dataTypes[ 0 ] ) || !inspected[ "*" ] && inspect( "*" ); } // A special extend for ajax options // that takes "flat" options (not to be deep extended) // Fixes #9887 function ajaxExtend( target, src ) { var key, deep, flatOptions = jQuery.ajaxSettings.flatOptions || {}; for ( key in src ) { if ( src[ key ] !== undefined ) { ( flatOptions[ key ] ? target : ( deep || ( deep = {} ) ) )[ key ] = src[ key ]; } } if ( deep ) { jQuery.extend( true, target, deep ); } return target; } /* Handles responses to an ajax request: * - finds the right dataType (mediates between content-type and expected dataType) * - returns the corresponding response */ function ajaxHandleResponses( s, jqXHR, responses ) { var ct, type, finalDataType, firstDataType, contents = s.contents, dataTypes = s.dataTypes; // Remove auto dataType and get content-type in the process while ( dataTypes[ 0 ] === "*" ) { dataTypes.shift(); if ( ct === undefined ) { ct = s.mimeType || jqXHR.getResponseHeader( "Content-Type" ); } } // Check if we're dealing with a known content-type if ( ct ) { for ( type in contents ) { if ( contents[ type ] && contents[ type ].test( ct ) ) { dataTypes.unshift( type ); break; } } } // Check to see if we have a response for the expected dataType if ( dataTypes[ 0 ] in responses ) { finalDataType = dataTypes[ 0 ]; } else { // Try convertible dataTypes for ( type in responses ) { if ( !dataTypes[ 0 ] || s.converters[ type + " " + dataTypes[ 0 ] ] ) { finalDataType = type; break; } if ( !firstDataType ) { firstDataType = type; } } // Or just use first one finalDataType = finalDataType || firstDataType; } // If we found a dataType // We add the dataType to the list if needed // and return the corresponding response if ( finalDataType ) { if ( finalDataType !== dataTypes[ 0 ] ) { dataTypes.unshift( finalDataType ); } return responses[ finalDataType ]; } } /* Chain conversions given the request and the original response * Also sets the responseXXX fields on the jqXHR instance */ function ajaxConvert( s, response, jqXHR, isSuccess ) { var conv2, current, conv, tmp, prev, converters = {}, // Work with a copy of dataTypes in case we need to modify it for conversion dataTypes = s.dataTypes.slice(); // Create converters map with lowercased keys if ( dataTypes[ 1 ] ) { for ( conv in s.converters ) { converters[ conv.toLowerCase() ] = s.converters[ conv ]; } } current = dataTypes.shift(); // Convert to each sequential dataType while ( current ) { if ( s.responseFields[ current ] ) { jqXHR[ s.responseFields[ current ] ] = response; } // Apply the dataFilter if provided if ( !prev && isSuccess && s.dataFilter ) { response = s.dataFilter( response, s.dataType ); } prev = current; current = dataTypes.shift(); if ( current ) { // There's only work to do if current dataType is non-auto if ( current === "*" ) { current = prev; // Convert response if prev dataType is non-auto and differs from current } else if ( prev !== "*" && prev !== current ) { // Seek a direct converter conv = converters[ prev + " " + current ] || converters[ "* " + current ]; // If none found, seek a pair if ( !conv ) { for ( conv2 in converters ) { // If conv2 outputs current tmp = conv2.split( " " ); if ( tmp[ 1 ] === current ) { // If prev can be converted to accepted input conv = converters[ prev + " " + tmp[ 0 ] ] || converters[ "* " + tmp[ 0 ] ]; if ( conv ) { // Condense equivalence converters if ( conv === true ) { conv = converters[ conv2 ]; // Otherwise, insert the intermediate dataType } else if ( converters[ conv2 ] !== true ) { current = tmp[ 0 ]; dataTypes.unshift( tmp[ 1 ] ); } break; } } } } // Apply converter (if not an equivalence) if ( conv !== true ) { // Unless errors are allowed to bubble, catch and return them if ( conv && s.throws ) { response = conv( response ); } else { try { response = conv( response ); } catch ( e ) { return { state: "parsererror", error: conv ? e : "No conversion from " + prev + " to " + current }; } } } } } } return { state: "success", data: response }; } jQuery.extend( { // Counter for holding the number of active queries active: 0, // Last-Modified header cache for next request lastModified: {}, etag: {}, ajaxSettings: { url: location.href, type: "GET", isLocal: rlocalProtocol.test( location.protocol ), global: true, processData: true, async: true, contentType: "application/x-www-form-urlencoded; charset=UTF-8", /* timeout: 0, data: null, dataType: null, username: null, password: null, cache: null, throws: false, traditional: false, headers: {}, */ accepts: { "*": allTypes, text: "text/plain", html: "text/html", xml: "application/xml, text/xml", json: "application/json, text/javascript" }, contents: { xml: /\bxml\b/, html: /\bhtml/, json: /\bjson\b/ }, responseFields: { xml: "responseXML", text: "responseText", json: "responseJSON" }, // Data converters // Keys separate source (or catchall "*") and destination types with a single space converters: { // Convert anything to text "* text": String, // Text to html (true = no transformation) "text html": true, // Evaluate text as a json expression "text json": JSON.parse, // Parse text as xml "text xml": jQuery.parseXML }, // For options that shouldn't be deep extended: // you can add your own custom options here if // and when you create one that shouldn't be // deep extended (see ajaxExtend) flatOptions: { url: true, context: true } }, // Creates a full fledged settings object into target // with both ajaxSettings and settings fields. // If target is omitted, writes into ajaxSettings. ajaxSetup: function( target, settings ) { return settings ? // Building a settings object ajaxExtend( ajaxExtend( target, jQuery.ajaxSettings ), settings ) : // Extending ajaxSettings ajaxExtend( jQuery.ajaxSettings, target ); }, ajaxPrefilter: addToPrefiltersOrTransports( prefilters ), ajaxTransport: addToPrefiltersOrTransports( transports ), // Main method ajax: function( url, options ) { // If url is an object, simulate pre-1.5 signature if ( typeof url === "object" ) { options = url; url = undefined; } // Force options to be an object options = options || {}; var transport, // URL without anti-cache param cacheURL, // Response headers responseHeadersString, responseHeaders, // timeout handle timeoutTimer, // Url cleanup var urlAnchor, // Request state (becomes false upon send and true upon completion) completed, // To know if global events are to be dispatched fireGlobals, // Loop variable i, // uncached part of the url uncached, // Create the final options object s = jQuery.ajaxSetup( {}, options ), // Callbacks context callbackContext = s.context || s, // Context for global events is callbackContext if it is a DOM node or jQuery collection globalEventContext = s.context && ( callbackContext.nodeType || callbackContext.jquery ) ? jQuery( callbackContext ) : jQuery.event, // Deferreds deferred = jQuery.Deferred(), completeDeferred = jQuery.Callbacks( "once memory" ), // Status-dependent callbacks statusCode = s.statusCode || {}, // Headers (they are sent all at once) requestHeaders = {}, requestHeadersNames = {}, // Default abort message strAbort = "canceled", // Fake xhr jqXHR = { readyState: 0, // Builds headers hashtable if needed getResponseHeader: function( key ) { var match; if ( completed ) { if ( !responseHeaders ) { responseHeaders = {}; while ( ( match = rheaders.exec( responseHeadersString ) ) ) { responseHeaders[ match[ 1 ].toLowerCase() + " " ] = ( responseHeaders[ match[ 1 ].toLowerCase() + " " ] || [] ) .concat( match[ 2 ] ); } } match = responseHeaders[ key.toLowerCase() + " " ]; } return match == null ? null : match.join( ", " ); }, // Raw string getAllResponseHeaders: function() { return completed ? responseHeadersString : null; }, // Caches the header setRequestHeader: function( name, value ) { if ( completed == null ) { name = requestHeadersNames[ name.toLowerCase() ] = requestHeadersNames[ name.toLowerCase() ] || name; requestHeaders[ name ] = value; } return this; }, // Overrides response content-type header overrideMimeType: function( type ) { if ( completed == null ) { s.mimeType = type; } return this; }, // Status-dependent callbacks statusCode: function( map ) { var code; if ( map ) { if ( completed ) { // Execute the appropriate callbacks jqXHR.always( map[ jqXHR.status ] ); } else { // Lazy-add the new callbacks in a way that preserves old ones for ( code in map ) { statusCode[ code ] = [ statusCode[ code ], map[ code ] ]; } } } return this; }, // Cancel the request abort: function( statusText ) { var finalText = statusText || strAbort; if ( transport ) { transport.abort( finalText ); } done( 0, finalText ); return this; } }; // Attach deferreds deferred.promise( jqXHR ); // Add protocol if not provided (prefilters might expect it) // Handle falsy url in the settings object (#10093: consistency with old signature) // We also use the url parameter if available s.url = ( ( url || s.url || location.href ) + "" ) .replace( rprotocol, location.protocol + "//" ); // Alias method option to type as per ticket #12004 s.type = options.method || options.type || s.method || s.type; // Extract dataTypes list s.dataTypes = ( s.dataType || "*" ).toLowerCase().match( rnothtmlwhite ) || [ "" ]; // A cross-domain request is in order when the origin doesn't match the current origin. if ( s.crossDomain == null ) { urlAnchor = document.createElement( "a" ); // Support: IE <=8 - 11, Edge 12 - 15 // IE throws exception on accessing the href property if url is malformed, // e.g. http://example.com:80x/ try { urlAnchor.href = s.url; // Support: IE <=8 - 11 only // Anchor's host property isn't correctly set when s.url is relative urlAnchor.href = urlAnchor.href; s.crossDomain = originAnchor.protocol + "//" + originAnchor.host !== urlAnchor.protocol + "//" + urlAnchor.host; } catch ( e ) { // If there is an error parsing the URL, assume it is crossDomain, // it can be rejected by the transport if it is invalid s.crossDomain = true; } } // Convert data if not already a string if ( s.data && s.processData && typeof s.data !== "string" ) { s.data = jQuery.param( s.data, s.traditional ); } // Apply prefilters inspectPrefiltersOrTransports( prefilters, s, options, jqXHR ); // If request was aborted inside a prefilter, stop there if ( completed ) { return jqXHR; } // We can fire global events as of now if asked to // Don't fire events if jQuery.event is undefined in an AMD-usage scenario (#15118) fireGlobals = jQuery.event && s.global; // Watch for a new set of requests if ( fireGlobals && jQuery.active++ === 0 ) { jQuery.event.trigger( "ajaxStart" ); } // Uppercase the type s.type = s.type.toUpperCase(); // Determine if request has content s.hasContent = !rnoContent.test( s.type ); // Save the URL in case we're toying with the If-Modified-Since // and/or If-None-Match header later on // Remove hash to simplify url manipulation cacheURL = s.url.replace( rhash, "" ); // More options handling for requests with no content if ( !s.hasContent ) { // Remember the hash so we can put it back uncached = s.url.slice( cacheURL.length ); // If data is available and should be processed, append data to url if ( s.data && ( s.processData || typeof s.data === "string" ) ) { cacheURL += ( rquery.test( cacheURL ) ? "&" : "?" ) + s.data; // #9682: remove data so that it's not used in an eventual retry delete s.data; } // Add or update anti-cache param if needed if ( s.cache === false ) { cacheURL = cacheURL.replace( rantiCache, "$1" ); uncached = ( rquery.test( cacheURL ) ? "&" : "?" ) + "_=" + ( nonce.guid++ ) + uncached; } // Put hash and anti-cache on the URL that will be requested (gh-1732) s.url = cacheURL + uncached; // Change '%20' to '+' if this is encoded form body content (gh-2658) } else if ( s.data && s.processData && ( s.contentType || "" ).indexOf( "application/x-www-form-urlencoded" ) === 0 ) { s.data = s.data.replace( r20, "+" ); } // Set the If-Modified-Since and/or If-None-Match header, if in ifModified mode. if ( s.ifModified ) { if ( jQuery.lastModified[ cacheURL ] ) { jqXHR.setRequestHeader( "If-Modified-Since", jQuery.lastModified[ cacheURL ] ); } if ( jQuery.etag[ cacheURL ] ) { jqXHR.setRequestHeader( "If-None-Match", jQuery.etag[ cacheURL ] ); } } // Set the correct header, if data is being sent if ( s.data && s.hasContent && s.contentType !== false || options.contentType ) { jqXHR.setRequestHeader( "Content-Type", s.contentType ); } // Set the Accepts header for the server, depending on the dataType jqXHR.setRequestHeader( "Accept", s.dataTypes[ 0 ] && s.accepts[ s.dataTypes[ 0 ] ] ? s.accepts[ s.dataTypes[ 0 ] ] + ( s.dataTypes[ 0 ] !== "*" ? ", " + allTypes + "; q=0.01" : "" ) : s.accepts[ "*" ] ); // Check for headers option for ( i in s.headers ) { jqXHR.setRequestHeader( i, s.headers[ i ] ); } // Allow custom headers/mimetypes and early abort if ( s.beforeSend && ( s.beforeSend.call( callbackContext, jqXHR, s ) === false || completed ) ) { // Abort if not done already and return return jqXHR.abort(); } // Aborting is no longer a cancellation strAbort = "abort"; // Install callbacks on deferreds completeDeferred.add( s.complete ); jqXHR.done( s.success ); jqXHR.fail( s.error ); // Get transport transport = inspectPrefiltersOrTransports( transports, s, options, jqXHR ); // If no transport, we auto-abort if ( !transport ) { done( -1, "No Transport" ); } else { jqXHR.readyState = 1; // Send global event if ( fireGlobals ) { globalEventContext.trigger( "ajaxSend", [ jqXHR, s ] ); } // If request was aborted inside ajaxSend, stop there if ( completed ) { return jqXHR; } // Timeout if ( s.async && s.timeout > 0 ) { timeoutTimer = window.setTimeout( function() { jqXHR.abort( "timeout" ); }, s.timeout ); } try { completed = false; transport.send( requestHeaders, done ); } catch ( e ) { // Rethrow post-completion exceptions if ( completed ) { throw e; } // Propagate others as results done( -1, e ); } } // Callback for when everything is done function done( status, nativeStatusText, responses, headers ) { var isSuccess, success, error, response, modified, statusText = nativeStatusText; // Ignore repeat invocations if ( completed ) { return; } completed = true; // Clear timeout if it exists if ( timeoutTimer ) { window.clearTimeout( timeoutTimer ); } // Dereference transport for early garbage collection // (no matter how long the jqXHR object will be used) transport = undefined; // Cache response headers responseHeadersString = headers || ""; // Set readyState jqXHR.readyState = status > 0 ? 4 : 0; // Determine if successful isSuccess = status >= 200 && status < 300 || status === 304; // Get response data if ( responses ) { response = ajaxHandleResponses( s, jqXHR, responses ); } // Use a noop converter for missing script but not if jsonp if ( !isSuccess && jQuery.inArray( "script", s.dataTypes ) > -1 && jQuery.inArray( "json", s.dataTypes ) < 0 ) { s.converters[ "text script" ] = function() {}; } // Convert no matter what (that way responseXXX fields are always set) response = ajaxConvert( s, response, jqXHR, isSuccess ); // If successful, handle type chaining if ( isSuccess ) { // Set the If-Modified-Since and/or If-None-Match header, if in ifModified mode. if ( s.ifModified ) { modified = jqXHR.getResponseHeader( "Last-Modified" ); if ( modified ) { jQuery.lastModified[ cacheURL ] = modified; } modified = jqXHR.getResponseHeader( "etag" ); if ( modified ) { jQuery.etag[ cacheURL ] = modified; } } // if no content if ( status === 204 || s.type === "HEAD" ) { statusText = "nocontent"; // if not modified } else if ( status === 304 ) { statusText = "notmodified"; // If we have data, let's convert it } else { statusText = response.state; success = response.data; error = response.error; isSuccess = !error; } } else { // Extract error from statusText and normalize for non-aborts error = statusText; if ( status || !statusText ) { statusText = "error"; if ( status < 0 ) { status = 0; } } } // Set data for the fake xhr object jqXHR.status = status; jqXHR.statusText = ( nativeStatusText || statusText ) + ""; // Success/Error if ( isSuccess ) { deferred.resolveWith( callbackContext, [ success, statusText, jqXHR ] ); } else { deferred.rejectWith( callbackContext, [ jqXHR, statusText, error ] ); } // Status-dependent callbacks jqXHR.statusCode( statusCode ); statusCode = undefined; if ( fireGlobals ) { globalEventContext.trigger( isSuccess ? "ajaxSuccess" : "ajaxError", [ jqXHR, s, isSuccess ? success : error ] ); } // Complete completeDeferred.fireWith( callbackContext, [ jqXHR, statusText ] ); if ( fireGlobals ) { globalEventContext.trigger( "ajaxComplete", [ jqXHR, s ] ); // Handle the global AJAX counter if ( !( --jQuery.active ) ) { jQuery.event.trigger( "ajaxStop" ); } } } return jqXHR; }, getJSON: function( url, data, callback ) { return jQuery.get( url, data, callback, "json" ); }, getScript: function( url, callback ) { return jQuery.get( url, undefined, callback, "script" ); } } ); jQuery.each( [ "get", "post" ], function( _i, method ) { jQuery[ method ] = function( url, data, callback, type ) { // Shift arguments if data argument was omitted if ( isFunction( data ) ) { type = type || callback; callback = data; data = undefined; } // The url can be an options object (which then must have .url) return jQuery.ajax( jQuery.extend( { url: url, type: method, dataType: type, data: data, success: callback }, jQuery.isPlainObject( url ) && url ) ); }; } ); jQuery.ajaxPrefilter( function( s ) { var i; for ( i in s.headers ) { if ( i.toLowerCase() === "content-type" ) { s.contentType = s.headers[ i ] || ""; } } } ); jQuery._evalUrl = function( url, options, doc ) { return jQuery.ajax( { url: url, // Make this explicit, since user can override this through ajaxSetup (#11264) type: "GET", dataType: "script", cache: true, async: false, global: false, // Only evaluate the response if it is successful (gh-4126) // dataFilter is not invoked for failure responses, so using it instead // of the default converter is kludgy but it works. converters: { "text script": function() {} }, dataFilter: function( response ) { jQuery.globalEval( response, options, doc ); } } ); }; jQuery.fn.extend( { wrapAll: function( html ) { var wrap; if ( this[ 0 ] ) { if ( isFunction( html ) ) { html = html.call( this[ 0 ] ); } // The elements to wrap the target around wrap = jQuery( html, this[ 0 ].ownerDocument ).eq( 0 ).clone( true ); if ( this[ 0 ].parentNode ) { wrap.insertBefore( this[ 0 ] ); } wrap.map( function() { var elem = this; while ( elem.firstElementChild ) { elem = elem.firstElementChild; } return elem; } ).append( this ); } return this; }, wrapInner: function( html ) { if ( isFunction( html ) ) { return this.each( function( i ) { jQuery( this ).wrapInner( html.call( this, i ) ); } ); } return this.each( function() { var self = jQuery( this ), contents = self.contents(); if ( contents.length ) { contents.wrapAll( html ); } else { self.append( html ); } } ); }, wrap: function( html ) { var htmlIsFunction = isFunction( html ); return this.each( function( i ) { jQuery( this ).wrapAll( htmlIsFunction ? html.call( this, i ) : html ); } ); }, unwrap: function( selector ) { this.parent( selector ).not( "body" ).each( function() { jQuery( this ).replaceWith( this.childNodes ); } ); return this; } } ); jQuery.expr.pseudos.hidden = function( elem ) { return !jQuery.expr.pseudos.visible( elem ); }; jQuery.expr.pseudos.visible = function( elem ) { return !!( elem.offsetWidth || elem.offsetHeight || elem.getClientRects().length ); }; jQuery.ajaxSettings.xhr = function() { try { return new window.XMLHttpRequest(); } catch ( e ) {} }; var xhrSuccessStatus = { // File protocol always yields status code 0, assume 200 0: 200, // Support: IE <=9 only // #1450: sometimes IE returns 1223 when it should be 204 1223: 204 }, xhrSupported = jQuery.ajaxSettings.xhr(); support.cors = !!xhrSupported && ( "withCredentials" in xhrSupported ); support.ajax = xhrSupported = !!xhrSupported; jQuery.ajaxTransport( function( options ) { var callback, errorCallback; // Cross domain only allowed if supported through XMLHttpRequest if ( support.cors || xhrSupported && !options.crossDomain ) { return { send: function( headers, complete ) { var i, xhr = options.xhr(); xhr.open( options.type, options.url, options.async, options.username, options.password ); // Apply custom fields if provided if ( options.xhrFields ) { for ( i in options.xhrFields ) { xhr[ i ] = options.xhrFields[ i ]; } } // Override mime type if needed if ( options.mimeType && xhr.overrideMimeType ) { xhr.overrideMimeType( options.mimeType ); } // X-Requested-With header // For cross-domain requests, seeing as conditions for a preflight are // akin to a jigsaw puzzle, we simply never set it to be sure. // (it can always be set on a per-request basis or even using ajaxSetup) // For same-domain requests, won't change header if already provided. if ( !options.crossDomain && !headers[ "X-Requested-With" ] ) { headers[ "X-Requested-With" ] = "XMLHttpRequest"; } // Set headers for ( i in headers ) { xhr.setRequestHeader( i, headers[ i ] ); } // Callback callback = function( type ) { return function() { if ( callback ) { callback = errorCallback = xhr.onload = xhr.onerror = xhr.onabort = xhr.ontimeout = xhr.onreadystatechange = null; if ( type === "abort" ) { xhr.abort(); } else if ( type === "error" ) { // Support: IE <=9 only // On a manual native abort, IE9 throws // errors on any property access that is not readyState if ( typeof xhr.status !== "number" ) { complete( 0, "error" ); } else { complete( // File: protocol always yields status 0; see #8605, #14207 xhr.status, xhr.statusText ); } } else { complete( xhrSuccessStatus[ xhr.status ] || xhr.status, xhr.statusText, // Support: IE <=9 only // IE9 has no XHR2 but throws on binary (trac-11426) // For XHR2 non-text, let the caller handle it (gh-2498) ( xhr.responseType || "text" ) !== "text" || typeof xhr.responseText !== "string" ? { binary: xhr.response } : { text: xhr.responseText }, xhr.getAllResponseHeaders() ); } } }; }; // Listen to events xhr.onload = callback(); errorCallback = xhr.onerror = xhr.ontimeout = callback( "error" ); // Support: IE 9 only // Use onreadystatechange to replace onabort // to handle uncaught aborts if ( xhr.onabort !== undefined ) { xhr.onabort = errorCallback; } else { xhr.onreadystatechange = function() { // Check readyState before timeout as it changes if ( xhr.readyState === 4 ) { // Allow onerror to be called first, // but that will not handle a native abort // Also, save errorCallback to a variable // as xhr.onerror cannot be accessed window.setTimeout( function() { if ( callback ) { errorCallback(); } } ); } }; } // Create the abort callback callback = callback( "abort" ); try { // Do send the request (this may raise an exception) xhr.send( options.hasContent && options.data || null ); } catch ( e ) { // #14683: Only rethrow if this hasn't been notified as an error yet if ( callback ) { throw e; } } }, abort: function() { if ( callback ) { callback(); } } }; } } ); // Prevent auto-execution of scripts when no explicit dataType was provided (See gh-2432) jQuery.ajaxPrefilter( function( s ) { if ( s.crossDomain ) { s.contents.script = false; } } ); // Install script dataType jQuery.ajaxSetup( { accepts: { script: "text/javascript, application/javascript, " + "application/ecmascript, application/x-ecmascript" }, contents: { script: /\b(?:java|ecma)script\b/ }, converters: { "text script": function( text ) { jQuery.globalEval( text ); return text; } } } ); // Handle cache's special case and crossDomain jQuery.ajaxPrefilter( "script", function( s ) { if ( s.cache === undefined ) { s.cache = false; } if ( s.crossDomain ) { s.type = "GET"; } } ); // Bind script tag hack transport jQuery.ajaxTransport( "script", function( s ) { // This transport only deals with cross domain or forced-by-attrs requests if ( s.crossDomain || s.scriptAttrs ) { var script, callback; return { send: function( _, complete ) { script = jQuery( "<script>" ) .attr( s.scriptAttrs || {} ) .prop( { charset: s.scriptCharset, src: s.url } ) .on( "load error", callback = function( evt ) { script.remove(); callback = null; if ( evt ) { complete( evt.type === "error" ? 404 : 200, evt.type ); } } ); // Use native DOM manipulation to avoid our domManip AJAX trickery document.head.appendChild( script[ 0 ] ); }, abort: function() { if ( callback ) { callback(); } } }; } } ); var oldCallbacks = [], rjsonp = /(=)\?(?=&|$)|\?\?/; // Default jsonp settings jQuery.ajaxSetup( { jsonp: "callback", jsonpCallback: function() { var callback = oldCallbacks.pop() || ( jQuery.expando + "_" + ( nonce.guid++ ) ); this[ callback ] = true; return callback; } } ); // Detect, normalize options and install callbacks for jsonp requests jQuery.ajaxPrefilter( "json jsonp", function( s, originalSettings, jqXHR ) { var callbackName, overwritten, responseContainer, jsonProp = s.jsonp !== false && ( rjsonp.test( s.url ) ? 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this : this.each( function( i ) { jQuery.offset.setOffset( this, options, i ); } ); } var rect, win, elem = this[ 0 ]; if ( !elem ) { return; } // Return zeros for disconnected and hidden (display: none) elements (gh-2310) // Support: IE <=11 only // Running getBoundingClientRect on a // disconnected node in IE throws an error if ( !elem.getClientRects().length ) { return { top: 0, left: 0 }; } // Get document-relative position by adding viewport scroll to viewport-relative gBCR rect = elem.getBoundingClientRect(); win = elem.ownerDocument.defaultView; return { top: rect.top + win.pageYOffset, left: rect.left + win.pageXOffset }; }, // position() relates an element's margin box to its offset parent's padding box // This corresponds to the behavior of CSS absolute positioning position: function() { if ( !this[ 0 ] ) { return; } var offsetParent, offset, doc, elem = this[ 0 ], parentOffset = { top: 0, left: 0 }; // position:fixed elements are offset from the viewport, which itself always has zero offset if ( jQuery.css( elem, "position" ) === "fixed" ) { // Assume position:fixed implies availability of getBoundingClientRect offset = elem.getBoundingClientRect(); } else { offset = this.offset(); // Account for the *real* offset parent, which can be the document or its root element // when a statically positioned element is identified doc = elem.ownerDocument; offsetParent = elem.offsetParent || doc.documentElement; while ( offsetParent && ( offsetParent === doc.body || offsetParent === doc.documentElement ) && jQuery.css( offsetParent, "position" ) === "static" ) { offsetParent = offsetParent.parentNode; } if ( offsetParent && offsetParent !== elem && offsetParent.nodeType === 1 ) { // Incorporate borders into its offset, since they are outside its content origin parentOffset = jQuery( offsetParent ).offset(); parentOffset.top += jQuery.css( offsetParent, "borderTopWidth", true ); parentOffset.left += jQuery.css( offsetParent, "borderLeftWidth", true ); } } // Subtract parent offsets and element margins return { top: offset.top - parentOffset.top - jQuery.css( elem, "marginTop", true ), left: offset.left - parentOffset.left - jQuery.css( elem, "marginLeft", true ) }; }, // This method will return documentElement in the following cases: // 1) For the element inside the iframe without offsetParent, this method will return // documentElement of the parent window // 2) For the hidden or detached element // 3) For body or html element, i.e. in case of the html node - it will return itself // // but those exceptions were never presented as a real life use-cases // and might be considered as more preferable results. // // This logic, however, is not guaranteed and can change at any point in the future offsetParent: function() { return this.map( function() { var offsetParent = this.offsetParent; while ( offsetParent && jQuery.css( offsetParent, "position" ) === "static" ) { offsetParent = offsetParent.offsetParent; } return offsetParent || documentElement; } ); } } ); // Create scrollLeft and scrollTop methods jQuery.each( { scrollLeft: "pageXOffset", scrollTop: "pageYOffset" }, function( method, prop ) { var top = "pageYOffset" === prop; jQuery.fn[ method ] = function( val ) { return access( this, function( elem, method, val ) { // Coalesce documents and windows var win; if ( isWindow( elem ) ) { win = elem; } else if ( elem.nodeType === 9 ) { win = elem.defaultView; } if ( val === undefined ) { return win ? win[ prop ] : elem[ method ]; } if ( win ) { win.scrollTo( !top ? val : win.pageXOffset, top ? val : win.pageYOffset ); } else { elem[ method ] = val; } }, method, val, arguments.length ); }; } ); // Support: Safari <=7 - 9.1, Chrome <=37 - 49 // Add the top/left cssHooks using jQuery.fn.position // Webkit bug: https://bugs.webkit.org/show_bug.cgi?id=29084 // Blink bug: https://bugs.chromium.org/p/chromium/issues/detail?id=589347 // getComputedStyle returns percent when specified for top/left/bottom/right; // rather than make the css module depend on the offset module, just check for it here jQuery.each( [ "top", "left" ], function( _i, prop ) { jQuery.cssHooks[ prop ] = addGetHookIf( support.pixelPosition, function( elem, computed ) { if ( computed ) { computed = curCSS( elem, prop ); // If curCSS returns percentage, fallback to offset return rnumnonpx.test( computed ) ? jQuery( elem ).position()[ prop ] + "px" : computed; } } ); } ); // Create innerHeight, innerWidth, height, width, outerHeight and outerWidth methods jQuery.each( { Height: "height", Width: "width" }, function( name, type ) { jQuery.each( { padding: "inner" + name, content: type, "": "outer" + name }, function( defaultExtra, funcName ) { // Margin is only for outerHeight, outerWidth jQuery.fn[ funcName ] = function( margin, value ) { var chainable = arguments.length && ( defaultExtra || typeof margin !== "boolean" ), extra = defaultExtra || ( margin === true || value === true ? "margin" : "border" ); return access( this, function( elem, type, value ) { var doc; if ( isWindow( elem ) ) { // $( window ).outerWidth/Height return w/h including scrollbars (gh-1729) return funcName.indexOf( "outer" ) === 0 ? elem[ "inner" + name ] : elem.document.documentElement[ "client" + name ]; } // Get document width or height if ( elem.nodeType === 9 ) { doc = elem.documentElement; // Either scroll[Width/Height] or offset[Width/Height] or client[Width/Height], // whichever is greatest return Math.max( elem.body[ "scroll" + name ], doc[ "scroll" + name ], elem.body[ "offset" + name ], doc[ "offset" + name ], doc[ "client" + name ] ); } return value === undefined ? // Get width or height on the element, requesting but not forcing parseFloat jQuery.css( elem, type, extra ) : // Set width or height on the element jQuery.style( elem, type, value, extra ); }, type, chainable ? margin : undefined, chainable ); }; } ); } ); jQuery.each( [ "ajaxStart", "ajaxStop", "ajaxComplete", "ajaxError", "ajaxSuccess", "ajaxSend" ], function( _i, type ) { jQuery.fn[ type ] = function( fn ) { return this.on( type, fn ); }; } ); jQuery.fn.extend( { bind: function( types, data, fn ) { return this.on( types, null, data, fn ); }, unbind: function( types, fn ) { return this.off( types, null, fn ); }, delegate: function( selector, types, data, fn ) { return this.on( types, selector, data, fn ); }, undelegate: function( selector, types, fn ) { // ( namespace ) or ( selector, types [, fn] ) return arguments.length === 1 ? this.off( selector, "**" ) : this.off( types, selector || "**", fn ); }, hover: function( fnOver, fnOut ) { return this.mouseenter( fnOver ).mouseleave( fnOut || fnOver ); } } ); jQuery.each( ( "blur focus focusin focusout resize scroll click dblclick " + "mousedown mouseup mousemove mouseover mouseout mouseenter mouseleave " + "change select submit keydown keypress keyup contextmenu" ).split( " " ), function( _i, name ) { // Handle event binding jQuery.fn[ name ] = function( data, fn ) { return arguments.length > 0 ? this.on( name, null, data, fn ) : this.trigger( name ); }; } ); // Support: Android <=4.0 only // Make sure we trim BOM and NBSP var rtrim = /^[\s\uFEFF\xA0]+|[\s\uFEFF\xA0]+$/g; // Bind a function to a context, optionally partially applying any // arguments. // jQuery.proxy is deprecated to promote standards (specifically Function#bind) // However, it is not slated for removal any time soon jQuery.proxy = function( fn, context ) { var tmp, args, proxy; if ( typeof context === "string" ) { tmp = fn[ context ]; context = fn; fn = tmp; } // Quick check to determine if target is callable, in the spec // this throws a TypeError, but we will just return undefined. if ( !isFunction( fn ) ) { return undefined; } // Simulated bind args = slice.call( arguments, 2 ); proxy = function() { return fn.apply( context || this, args.concat( slice.call( arguments ) ) ); }; // Set the guid of unique handler to the same of original handler, so it can be removed proxy.guid = fn.guid = fn.guid || jQuery.guid++; return proxy; }; jQuery.holdReady = function( hold ) { if ( hold ) { jQuery.readyWait++; } else { jQuery.ready( true ); } }; jQuery.isArray = Array.isArray; jQuery.parseJSON = JSON.parse; jQuery.nodeName = nodeName; jQuery.isFunction = isFunction; jQuery.isWindow = isWindow; jQuery.camelCase = camelCase; jQuery.type = toType; jQuery.now = Date.now; jQuery.isNumeric = function( obj ) { // As of jQuery 3.0, isNumeric is limited to // strings and numbers (primitives or objects) // that can be coerced to finite numbers (gh-2662) var type = jQuery.type( obj ); return ( type === "number" || type === "string" ) && // parseFloat NaNs numeric-cast false positives ("") // ...but misinterprets leading-number strings, particularly hex literals ("0x...") // subtraction forces infinities to NaN !isNaN( obj - parseFloat( obj ) ); }; jQuery.trim = function( text ) { return text == null ? 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html/_static/js/versions.js (deleted)
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@@ -1,228 +0,0 @@const themeFlyoutDisplay = "hidden"; const themeVersionSelector = true; const themeLanguageSelector = true; if (themeFlyoutDisplay === "attached") { function renderLanguages(config) { if (!config.projects.translations.length) { return ""; } // Insert the current language to the options on the selector let languages = config.projects.translations.concat(config.projects.current); languages = languages.sort((a, b) => a.language.name.localeCompare(b.language.name)); const languagesHTML = ` <dl> <dt>Languages</dt> ${languages .map( (translation) => ` <dd ${translation.slug == config.projects.current.slug ? 'class="rtd-current-item"' : ""}> <a href="${translation.urls.documentation}">${translation.language.code}</a> </dd> `, ) .join("\n")} </dl> `; return languagesHTML; } function renderVersions(config) { if (!config.versions.active.length) { return ""; } const versionsHTML = ` <dl> <dt>Versions</dt> ${config.versions.active .map( (version) => ` <dd ${version.slug === config.versions.current.slug ? 'class="rtd-current-item"' : ""}> <a href="${version.urls.documentation}">${version.slug}</a> </dd> `, ) .join("\n")} </dl> `; return versionsHTML; } function renderDownloads(config) { if (!Object.keys(config.versions.current.downloads).length) { return ""; } const downloadsNameDisplay = { pdf: "PDF", epub: "Epub", htmlzip: "HTML", }; const downloadsHTML = ` <dl> <dt>Downloads</dt> ${Object.entries(config.versions.current.downloads) .map( ([name, url]) => ` <dd> <a href="${url}">${downloadsNameDisplay[name]}</a> </dd> `, ) .join("\n")} </dl> `; return downloadsHTML; } document.addEventListener("readthedocs-addons-data-ready", function (event) { const config = event.detail.data(); const flyout = ` <div class="rst-versions" data-toggle="rst-versions" role="note"> <span class="rst-current-version" data-toggle="rst-current-version"> <span class="fa fa-book"> Read the Docs</span> v: ${config.versions.current.slug} <span class="fa fa-caret-down"></span> </span> <div class="rst-other-versions"> <div class="injected"> ${renderLanguages(config)} ${renderVersions(config)} ${renderDownloads(config)} <dl> <dt>On Read the Docs</dt> <dd> <a href="${config.projects.current.urls.home}">Project Home</a> </dd> <dd> <a href="${config.projects.current.urls.builds}">Builds</a> </dd> <dd> <a href="${config.projects.current.urls.downloads}">Downloads</a> </dd> </dl> <dl> <dt>Search</dt> <dd> <form id="flyout-search-form"> <input class="wy-form" type="text" name="q" aria-label="Search docs" placeholder="Search docs" /> </form> </dd> </dl> <hr /> <small> <span>Hosted by <a href="https://about.readthedocs.org/?utm_source=&utm_content=flyout">Read the Docs</a></span> </small> </div> </div> `; // Inject the generated flyout into the body HTML element. document.body.insertAdjacentHTML("beforeend", flyout); // Trigger the Read the Docs Addons Search modal when clicking on the "Search docs" input from inside the flyout. document .querySelector("#flyout-search-form") .addEventListener("focusin", () => { const event = new CustomEvent("readthedocs-search-show"); document.dispatchEvent(event); }); }) } if (themeLanguageSelector || themeVersionSelector) { function onSelectorSwitch(event) { const option = event.target.selectedIndex; const item = event.target.options[option]; window.location.href = item.dataset.url; } document.addEventListener("readthedocs-addons-data-ready", function (event) { const config = event.detail.data(); const versionSwitch = document.querySelector( "div.switch-menus > div.version-switch", ); if (themeVersionSelector) { let versions = config.versions.active; if (config.versions.current.hidden || config.versions.current.type === "external") { versions.unshift(config.versions.current); } const versionSelect = ` <select> ${versions .map( (version) => ` <option value="${version.slug}" ${config.versions.current.slug === version.slug ? 'selected="selected"' : ""} data-url="${version.urls.documentation}"> ${version.slug} </option>`, ) .join("\n")} </select> `; versionSwitch.innerHTML = versionSelect; versionSwitch.firstElementChild.addEventListener("change", onSelectorSwitch); } const languageSwitch = document.querySelector( "div.switch-menus > div.language-switch", ); if (themeLanguageSelector) { if (config.projects.translations.length) { // Add the current language to the options on the selector let languages = config.projects.translations.concat( config.projects.current, ); languages = languages.sort((a, b) => a.language.name.localeCompare(b.language.name), ); const languageSelect = ` <select> ${languages .map( (language) => ` <option value="${language.language.code}" ${config.projects.current.slug === language.slug ? 'selected="selected"' : ""} data-url="${language.urls.documentation}"> ${language.language.name} </option>`, ) .join("\n")} </select> `; languageSwitch.innerHTML = languageSelect; languageSwitch.firstElementChild.addEventListener("change", onSelectorSwitch); } else { languageSwitch.remove(); } } }); } document.addEventListener("readthedocs-addons-data-ready", function (event) { // Trigger the Read the Docs Addons Search modal when clicking on "Search docs" input from the topnav. document .querySelector("[role='search'] input") .addEventListener("focusin", () => { const event = new CustomEvent("readthedocs-search-show"); document.dispatchEvent(event); }); });
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@@ -1,12 +1,19 @@/* * language_data.js * ~~~~~~~~~~~~~~~~ * * This script contains the language-specific data used by searchtools.js, * namely the list of stopwords, stemmer, scorer and splitter. * * :copyright: Copyright 2007-2022 by the Sphinx team, see AUTHORS. * :license: BSD, see LICENSE for details. * */ var stopwords = ["a", "and", "are", "as", "at", "be", "but", "by", "for", "if", "in", "into", "is", "it", "near", "no", "not", "of", "on", "or", "such", "that", "the", "their", "then", "there", "these", "they", "this", "to", "was", "will", "with"]; /* Non-minified version is copied as a separate JS file, if available */ /* Non-minified version is copied as a separate JS file, is available */ /** * Porter Stemmer
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@@ -17,7 +17,6 @@ span.linenos.special { color: #000000; background-color: #ffffc0; padding-left:.highlight .cs { color: #3D7B7B; font-style: italic } /* Comment.Special */ .highlight .gd { color: #A00000 } /* Generic.Deleted */ .highlight .ge { font-style: italic } /* Generic.Emph */ .highlight .ges { font-weight: bold; font-style: italic } /* Generic.EmphStrong */ .highlight .gr { color: #E40000 } /* Generic.Error */ .highlight .gh { color: #000080; font-weight: bold } /* Generic.Heading */ .highlight .gi { color: #008400 } /* Generic.Inserted */
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@@ -1,5 +1,12 @@/* * searchtools.js * ~~~~~~~~~~~~~~~~ * * Sphinx JavaScript utilities for the full-text search. * * :copyright: Copyright 2007-2022 by the Sphinx team, see AUTHORS. * :license: BSD, see LICENSE for details. * */ "use strict";
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@@ -13,7 +20,7 @@ if (typeof Scorer === "undefined") {// and returns the new score. /* score: result => { const [docname, title, anchor, descr, score, filename, kind] = result const [docname, title, anchor, descr, score, filename] = result return score }, */
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@@ -40,14 +47,6 @@ if (typeof Scorer === "undefined") {}; } // Global search result kind enum, used by themes to style search results. class SearchResultKind { static get index() { return "index"; } static get object() { return "object"; } static get text() { return "text"; } static get title() { return "title"; } } const _removeChildren = (element) => { while (element && element.lastChild) element.removeChild(element.lastChild); };
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@@ -58,20 +57,16 @@ const _removeChildren = (element) => {const _escapeRegExp = (string) => string.replace(/[.*+\-?^${}()|[\]\\]/g, "\\$&"); // $& means the whole matched string const _displayItem = (item, searchTerms, highlightTerms) => { const _displayItem = (item, highlightTerms, searchTerms) => { const docBuilder = DOCUMENTATION_OPTIONS.BUILDER; const docUrlRoot = DOCUMENTATION_OPTIONS.URL_ROOT; const docFileSuffix = DOCUMENTATION_OPTIONS.FILE_SUFFIX; const docLinkSuffix = DOCUMENTATION_OPTIONS.LINK_SUFFIX; const showSearchSummary = DOCUMENTATION_OPTIONS.SHOW_SEARCH_SUMMARY; const contentRoot = document.documentElement.dataset.content_root; const [docName, title, anchor, descr, score, _filename, kind] = item; const [docName, title, anchor, descr] = item; let listItem = document.createElement("li"); // Add a class representing the item's type: // can be used by a theme's CSS selector for styling // See SearchResultKind for the class names. listItem.classList.add(`kind-${kind}`); let requestUrl; let linkUrl; if (docBuilder === "dirhtml") {
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@@ -80,35 +75,29 @@ const _displayItem = (item, searchTerms, highlightTerms) => {if (dirname.match(/\/index\/$/)) dirname = dirname.substring(0, dirname.length - 6); else if (dirname === "index/") dirname = ""; requestUrl = contentRoot + dirname; requestUrl = docUrlRoot + dirname; linkUrl = requestUrl; } else { // normal html builders requestUrl = contentRoot + docName + docFileSuffix; requestUrl = docUrlRoot + docName + docFileSuffix; linkUrl = docName + docLinkSuffix; } const params = new URLSearchParams(); params.set("highlight", [...highlightTerms].join(" ")); let linkEl = listItem.appendChild(document.createElement("a")); linkEl.href = linkUrl + anchor; linkEl.dataset.score = score; linkEl.href = linkUrl + "?" + params.toString() + anchor; linkEl.innerHTML = title; if (descr) { listItem.appendChild(document.createElement("span")).innerHTML = if (descr) listItem.appendChild(document.createElement("span")).innerText = " (" + descr + ")"; // highlight search terms in the description if (SPHINX_HIGHLIGHT_ENABLED) // set in sphinx_highlight.js highlightTerms.forEach((term) => _highlightText(listItem, term, "highlighted")); } else if (showSearchSummary) fetch(requestUrl) .then((responseData) => responseData.text()) .then((data) => { if (data) listItem.appendChild( Search.makeSearchSummary(data, searchTerms, anchor) Search.makeSearchSummary(data, searchTerms, highlightTerms) ); // highlight search terms in the summary if (SPHINX_HIGHLIGHT_ENABLED) // set in sphinx_highlight.js highlightTerms.forEach((term) => _highlightText(listItem, term, "highlighted")); }); Search.output.appendChild(listItem); };
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@@ -120,46 +109,28 @@ const _finishSearch = (resultCount) => {"Your search did not match any documents. Please make sure that all words are spelled correctly and that you've selected enough categories." ); else Search.status.innerText = Documentation.ngettext( "Search finished, found one page matching the search query.", "Search finished, found ${resultCount} pages matching the search query.", resultCount, ).replace('${resultCount}', resultCount); Search.status.innerText = _( `Search finished, found ${resultCount} page(s) matching the search query.` ); }; const _displayNextItem = ( results, resultCount, searchTerms, highlightTerms, searchTerms ) => { // results left, load the summary and display it // this is intended to be dynamic (don't sub resultsCount) if (results.length) { _displayItem(results.pop(), searchTerms, highlightTerms); _displayItem(results.pop(), highlightTerms, searchTerms); setTimeout( () => _displayNextItem(results, resultCount, searchTerms, highlightTerms), () => _displayNextItem(results, resultCount, highlightTerms, searchTerms), 5 ); } // search finished, update title and status message else _finishSearch(resultCount); }; // Helper function used by query() to order search results. // Each input is an array of [docname, title, anchor, descr, score, filename, kind]. // Order the results by score (in opposite order of appearance, since the // `_displayNextItem` function uses pop() to retrieve items) and then alphabetically. const _orderResultsByScoreThenName = (a, b) => { const leftScore = a[4]; const rightScore = b[4]; if (leftScore === rightScore) { // same score: sort alphabetically const leftTitle = a[1].toLowerCase(); const rightTitle = b[1].toLowerCase(); if (leftTitle === rightTitle) return 0; return leftTitle > rightTitle ? -1 : 1; // inverted is intentional } return leftScore > rightScore ? 1 : -1; }; /** * Default splitQuery function. Can be overridden in ``sphinx.search`` with a
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@@ -183,26 +154,15 @@ const Search = {_queued_query: null, _pulse_status: -1, htmlToText: (htmlString, anchor) => { const htmlElement = new DOMParser().parseFromString(htmlString, 'text/html'); for (const removalQuery of [".headerlink", "script", "style"]) { htmlElement.querySelectorAll(removalQuery).forEach((el) => { el.remove() }); } if (anchor) { const anchorContent = htmlElement.querySelector(`[role="main"] ${anchor}`); if (anchorContent) return anchorContent.textContent; console.warn( `Anchored content block not found. Sphinx search tries to obtain it via DOM query '[role=main] ${anchor}'. Check your theme or template.` ); } // if anchor not specified or not found, fall back to main content htmlToText: (htmlString) => { const htmlElement = document .createRange() .createContextualFragment(htmlString); _removeChildren(htmlElement.querySelectorAll(".headerlink")); const docContent = htmlElement.querySelector('[role="main"]'); if (docContent) return docContent.textContent; if (docContent !== undefined) return docContent.textContent; console.warn( "Content block not found. Sphinx search tries to obtain it via DOM query '[role=main]'. Check your theme or template." "Content block not found. Sphinx search tries to obtain it via '[role=main]'. Could you check your theme or template." ); return ""; },
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@@ -255,7 +215,6 @@ const Search = {searchSummary.classList.add("search-summary"); searchSummary.innerText = ""; const searchList = document.createElement("ul"); searchList.setAttribute("role", "list"); searchList.classList.add("search"); const out = document.getElementById("search-results");
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@@ -276,7 +235,10 @@ const Search = {else Search.deferQuery(query); }, _parseQuery: (query) => { /** * execute search (requires search index to be loaded) */ query: (query) => { // stem the search terms and add them to the correct list const stemmer = new Stemmer(); const searchTerms = new Set();
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@@ -304,98 +266,40 @@ const Search = {} }); if (SPHINX_HIGHLIGHT_ENABLED) { // set in sphinx_highlight.js localStorage.setItem("sphinx_highlight_terms", [...highlightTerms].join(" ")) } // console.debug("SEARCH: searching for:"); // console.info("required: ", [...searchTerms]); // console.info("excluded: ", [...excludedTerms]); return [query, searchTerms, excludedTerms, highlightTerms, objectTerms]; }, /** * execute search (requires search index to be loaded) */ _performSearch: (query, searchTerms, excludedTerms, highlightTerms, objectTerms) => { const filenames = Search._index.filenames; const docNames = Search._index.docnames; const titles = Search._index.titles; const allTitles = Search._index.alltitles; const indexEntries = Search._index.indexentries; // Collect multiple result groups to be sorted separately and then ordered. // Each is an array of [docname, title, anchor, descr, score, filename, kind]. const normalResults = []; const nonMainIndexResults = []; // array of [docname, title, anchor, descr, score, filename] let results = []; _removeChildren(document.getElementById("search-progress")); const queryLower = query.toLowerCase().trim(); for (const [title, foundTitles] of Object.entries(allTitles)) { if (title.toLowerCase().trim().includes(queryLower) && (queryLower.length >= title.length/2)) { for (const [file, id] of foundTitles) { const score = Math.round(Scorer.title * queryLower.length / title.length); const boost = titles[file] === title ? 1 : 0; // add a boost for document titles normalResults.push([ docNames[file], titles[file] !== title ? `${titles[file]} > ${title}` : title, id !== null ? "#" + id : "", null, score + boost, filenames[file], SearchResultKind.title, ]); } } } // search for explicit entries in index directives for (const [entry, foundEntries] of Object.entries(indexEntries)) { if (entry.includes(queryLower) && (queryLower.length >= entry.length/2)) { for (const [file, id, isMain] of foundEntries) { const score = Math.round(100 * queryLower.length / entry.length); const result = [ docNames[file], titles[file], id ? "#" + id : "", null, score, filenames[file], SearchResultKind.index, ]; if (isMain) { normalResults.push(result); } else { nonMainIndexResults.push(result); } } } } // lookup as object objectTerms.forEach((term) => normalResults.push(...Search.performObjectSearch(term, objectTerms)) results.push(...Search.performObjectSearch(term, objectTerms)) ); // lookup as search terms in fulltext normalResults.push(...Search.performTermsSearch(searchTerms, excludedTerms)); results.push(...Search.performTermsSearch(searchTerms, excludedTerms)); // let the scorer override scores with a custom scoring function if (Scorer.score) { normalResults.forEach((item) => (item[4] = Scorer.score(item))); nonMainIndexResults.forEach((item) => (item[4] = Scorer.score(item))); } // Sort each group of results by score and then alphabetically by name. normalResults.sort(_orderResultsByScoreThenName); nonMainIndexResults.sort(_orderResultsByScoreThenName); // Combine the result groups in (reverse) order. // Non-main index entries are typically arbitrary cross-references, // so display them after other results. let results = [...nonMainIndexResults, ...normalResults]; if (Scorer.score) results.forEach((item) => (item[4] = Scorer.score(item))); // now sort the results by score (in opposite order of appearance, since the // display function below uses pop() to retrieve items) and then // alphabetically results.sort((a, b) => { const leftScore = a[4]; const rightScore = b[4]; if (leftScore === rightScore) { // same score: sort alphabetically const leftTitle = a[1].toLowerCase(); const rightTitle = b[1].toLowerCase(); if (leftTitle === rightTitle) return 0; return leftTitle > rightTitle ? -1 : 1; // inverted is intentional } return leftScore > rightScore ? 1 : -1; }); // remove duplicate search results // note the reversing of results, so that in the case of duplicates, the highest-scoring entry is kept
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@@ -409,19 +313,14 @@ const Search = {return acc; }, []); return results.reverse(); }, query: (query) => { const [searchQuery, searchTerms, excludedTerms, highlightTerms, objectTerms] = Search._parseQuery(query); const results = Search._performSearch(searchQuery, searchTerms, excludedTerms, highlightTerms, objectTerms); results = results.reverse(); // for debugging //Search.lastresults = results.slice(); // a copy // console.info("search results:", Search.lastresults); // print the results _displayNextItem(results, results.length, searchTerms, highlightTerms); _displayNextItem(results, results.length, highlightTerms, searchTerms); }, /**
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@@ -485,7 +384,6 @@ const Search = {descr, score, filenames[match[0]], SearchResultKind.object, ]); }; Object.keys(objects).forEach((prefix) =>
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@@ -503,8 +401,8 @@ const Search = {// prepare search const terms = Search._index.terms; const titleTerms = Search._index.titleterms; const filenames = Search._index.filenames; const docNames = Search._index.docnames; const filenames = Search._index.filenames; const titles = Search._index.titles; const scoreMap = new Map();
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@@ -520,18 +418,14 @@ const Search = {// add support for partial matches if (word.length > 2) { const escapedWord = _escapeRegExp(word); if (!terms.hasOwnProperty(word)) { Object.keys(terms).forEach((term) => { if (term.match(escapedWord)) arr.push({ files: terms[term], score: Scorer.partialTerm }); }); } if (!titleTerms.hasOwnProperty(word)) { Object.keys(titleTerms).forEach((term) => { if (term.match(escapedWord)) arr.push({ files: titleTerms[term], score: Scorer.partialTitle }); }); } Object.keys(terms).forEach((term) => { if (term.match(escapedWord) && !terms[word]) arr.push({ files: terms[term], score: Scorer.partialTerm }); }); Object.keys(titleTerms).forEach((term) => { if (term.match(escapedWord) && !titleTerms[word]) arr.push({ files: titleTerms[word], score: Scorer.partialTitle }); }); } // no match but word was a required one
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@@ -554,8 +448,9 @@ const Search = {// create the mapping files.forEach((file) => { if (!fileMap.has(file)) fileMap.set(file, [word]); else if (fileMap.get(file).indexOf(word) === -1) fileMap.get(file).push(word); if (fileMap.has(file) && fileMap.get(file).indexOf(word) === -1) fileMap.get(file).push(word); else fileMap.set(file, [word]); }); });
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@@ -596,7 +491,6 @@ const Search = {null, score, filenames[file], SearchResultKind.text, ]); } return results;
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@@ -605,15 +499,16 @@ const Search = {/** * helper function to return a node containing the * search summary for a given text. keywords is a list * of stemmed words. * of stemmed words, highlightWords is the list of normal, unstemmed * words. the first one is used to find the occurrence, the * latter for highlighting it. */ makeSearchSummary: (htmlText, keywords, anchor) => { const text = Search.htmlToText(htmlText, anchor); makeSearchSummary: (htmlText, keywords, highlightWords) => { const text = Search.htmlToText(htmlText).toLowerCase(); if (text === "") return null; const textLower = text.toLowerCase(); const actualStartPosition = [...keywords] .map((k) => textLower.indexOf(k.toLowerCase())) .map((k) => text.indexOf(k.toLowerCase())) .filter((i) => i > -1) .slice(-1)[0]; const startWithContext = Math.max(actualStartPosition - 120, 0);
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@@ -621,9 +516,13 @@ const Search = {const top = startWithContext === 0 ? "" : "..."; const tail = startWithContext + 240 < text.length ? "..." : ""; let summary = document.createElement("p"); let summary = document.createElement("div"); summary.classList.add("context"); summary.textContent = top + text.substr(startWithContext, 240).trim() + tail; summary.innerText = top + text.substr(startWithContext, 240).trim() + tail; highlightWords.forEach((highlightWord) => _highlightText(summary, highlightWord, "highlighted") ); return summary; },
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html/_static/sphinx_highlight.js (deleted)
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@@ -1,154 +0,0 @@/* Highlighting utilities for Sphinx HTML documentation. */ "use strict"; const SPHINX_HIGHLIGHT_ENABLED = true /** * highlight a given string on a node by wrapping it in * span elements with the given class name. */ const _highlight = (node, addItems, text, className) => { if (node.nodeType === Node.TEXT_NODE) { const val = node.nodeValue; const parent = node.parentNode; const pos = val.toLowerCase().indexOf(text); if ( pos >= 0 && !parent.classList.contains(className) && !parent.classList.contains("nohighlight") ) { let span; const closestNode = parent.closest("body, svg, foreignObject"); const isInSVG = closestNode && closestNode.matches("svg"); if (isInSVG) { span = document.createElementNS("http://www.w3.org/2000/svg", "tspan"); } else { span = document.createElement("span"); span.classList.add(className); } span.appendChild(document.createTextNode(val.substr(pos, text.length))); const rest = document.createTextNode(val.substr(pos + text.length)); parent.insertBefore( span, parent.insertBefore( rest, node.nextSibling ) ); node.nodeValue = val.substr(0, pos); /* There may be more occurrences of search term in this node. So call this * function recursively on the remaining fragment. */ _highlight(rest, addItems, text, className); if (isInSVG) { const rect = document.createElementNS( "http://www.w3.org/2000/svg", "rect" ); const bbox = parent.getBBox(); rect.x.baseVal.value = bbox.x; rect.y.baseVal.value = bbox.y; rect.width.baseVal.value = bbox.width; rect.height.baseVal.value = bbox.height; rect.setAttribute("class", className); addItems.push({ parent: parent, target: rect }); } } } else if (node.matches && !node.matches("button, select, textarea")) { node.childNodes.forEach((el) => _highlight(el, addItems, text, className)); } }; const _highlightText = (thisNode, text, className) => { let addItems = []; _highlight(thisNode, addItems, text, className); addItems.forEach((obj) => obj.parent.insertAdjacentElement("beforebegin", obj.target) ); }; /** * Small JavaScript module for the documentation. */ const SphinxHighlight = { /** * highlight the search words provided in localstorage in the text */ highlightSearchWords: () => { if (!SPHINX_HIGHLIGHT_ENABLED) return; // bail if no highlight // get and clear terms from localstorage const url = new URL(window.location); const highlight = localStorage.getItem("sphinx_highlight_terms") || url.searchParams.get("highlight") || ""; localStorage.removeItem("sphinx_highlight_terms") url.searchParams.delete("highlight"); window.history.replaceState({}, "", url); // get individual terms from highlight string const terms = highlight.toLowerCase().split(/\s+/).filter(x => x); if (terms.length === 0) return; // nothing to do // There should never be more than one element matching "div.body" const divBody = document.querySelectorAll("div.body"); const body = divBody.length ? divBody[0] : document.querySelector("body"); window.setTimeout(() => { terms.forEach((term) => _highlightText(body, term, "highlighted")); }, 10); const searchBox = document.getElementById("searchbox"); if (searchBox === null) return; searchBox.appendChild( document .createRange() .createContextualFragment( '<p class="highlight-link">' + '<a href="javascript:SphinxHighlight.hideSearchWords()">' + _("Hide Search Matches") + "</a></p>" ) ); }, /** * helper function to hide the search marks again */ hideSearchWords: () => { document .querySelectorAll("#searchbox .highlight-link") .forEach((el) => el.remove()); document .querySelectorAll("span.highlighted") .forEach((el) => el.classList.remove("highlighted")); localStorage.removeItem("sphinx_highlight_terms") }, initEscapeListener: () => { // only install a listener if it is really needed if (!DOCUMENTATION_OPTIONS.ENABLE_SEARCH_SHORTCUTS) return; document.addEventListener("keydown", (event) => { // bail for input elements if (BLACKLISTED_KEY_CONTROL_ELEMENTS.has(document.activeElement.tagName)) return; // bail with special keys if (event.shiftKey || event.altKey || event.ctrlKey || event.metaKey) return; if (DOCUMENTATION_OPTIONS.ENABLE_SEARCH_SHORTCUTS && (event.key === "Escape")) { SphinxHighlight.hideSearchWords(); event.preventDefault(); } }); }, }; _ready(() => { /* Do not call highlightSearchWords() when we are on the search page. * It will highlight words from the *previous* search query. */ if (typeof Search === "undefined") SphinxHighlight.highlightSearchWords(); SphinxHighlight.initEscapeListener(); });
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@@ -0,0 +1,2042 @@(function (global, factory) { typeof exports === 'object' && typeof module !== 'undefined' ? module.exports = factory() : typeof define === 'function' && define.amd ? define('underscore', factory) : (global = typeof globalThis !== 'undefined' ? globalThis : global || self, (function () { var current = global._; var exports = global._ = factory(); exports.noConflict = function () { global._ = current; return exports; }; }())); }(this, (function () { // Underscore.js 1.13.1 // https://underscorejs.org // (c) 2009-2021 Jeremy Ashkenas, Julian Gonggrijp, and DocumentCloud and Investigative Reporters & Editors // Underscore may be freely distributed under the MIT license. // Current version. var VERSION = '1.13.1'; // Establish the root object, `window` (`self`) in the browser, `global` // on the server, or `this` in some virtual machines. We use `self` // instead of `window` for `WebWorker` support. var root = typeof self == 'object' && self.self === self && self || typeof global == 'object' && global.global === global && global || Function('return this')() || {}; // Save bytes in the minified (but not gzipped) version: var ArrayProto = Array.prototype, ObjProto = Object.prototype; var SymbolProto = typeof Symbol !== 'undefined' ? Symbol.prototype : null; // Create quick reference variables for speed access to core prototypes. var push = ArrayProto.push, slice = ArrayProto.slice, toString = ObjProto.toString, hasOwnProperty = ObjProto.hasOwnProperty; // Modern feature detection. var supportsArrayBuffer = typeof ArrayBuffer !== 'undefined', supportsDataView = typeof DataView !== 'undefined'; // All **ECMAScript 5+** native function implementations that we hope to use // are declared here. var nativeIsArray = Array.isArray, nativeKeys = Object.keys, nativeCreate = Object.create, nativeIsView = supportsArrayBuffer && ArrayBuffer.isView; // Create references to these builtin functions because we override them. var _isNaN = isNaN, _isFinite = isFinite; // Keys in IE < 9 that won't be iterated by `for key in ...` and thus missed. var hasEnumBug = !{toString: null}.propertyIsEnumerable('toString'); var nonEnumerableProps = ['valueOf', 'isPrototypeOf', 'toString', 'propertyIsEnumerable', 'hasOwnProperty', 'toLocaleString']; // The largest integer that can be represented exactly. var MAX_ARRAY_INDEX = Math.pow(2, 53) - 1; // Some functions take a variable number of arguments, or a few expected // arguments at the beginning and then a variable number of values to operate // on. This helper accumulates all remaining arguments past the function’s // argument length (or an explicit `startIndex`), into an array that becomes // the last argument. Similar to ES6’s "rest parameter". function restArguments(func, startIndex) { startIndex = startIndex == null ? func.length - 1 : +startIndex; return function() { var length = Math.max(arguments.length - startIndex, 0), rest = Array(length), index = 0; for (; index < length; index++) { rest[index] = arguments[index + startIndex]; } switch (startIndex) { case 0: return func.call(this, rest); case 1: return func.call(this, arguments[0], rest); case 2: return func.call(this, arguments[0], arguments[1], rest); } var args = Array(startIndex + 1); for (index = 0; index < startIndex; index++) { args[index] = arguments[index]; } args[startIndex] = rest; return func.apply(this, args); }; } // Is a given variable an object? function isObject(obj) { var type = typeof obj; return type === 'function' || type === 'object' && !!obj; } // Is a given value equal to null? function isNull(obj) { return obj === null; } // Is a given variable undefined? function isUndefined(obj) { return obj === void 0; } // Is a given value a boolean? function isBoolean(obj) { return obj === true || obj === false || toString.call(obj) === '[object Boolean]'; } // Is a given value a DOM element? function isElement(obj) { return !!(obj && obj.nodeType === 1); } // Internal function for creating a `toString`-based type tester. function tagTester(name) { var tag = '[object ' + name + ']'; return function(obj) { return toString.call(obj) === tag; }; } var isString = tagTester('String'); var isNumber = tagTester('Number'); var isDate = tagTester('Date'); var isRegExp = tagTester('RegExp'); var isError = tagTester('Error'); var isSymbol = tagTester('Symbol'); var isArrayBuffer = tagTester('ArrayBuffer'); var isFunction = tagTester('Function'); // Optimize `isFunction` if appropriate. Work around some `typeof` bugs in old // v8, IE 11 (#1621), Safari 8 (#1929), and PhantomJS (#2236). var nodelist = root.document && root.document.childNodes; if (typeof /./ != 'function' && typeof Int8Array != 'object' && typeof nodelist != 'function') { isFunction = function(obj) { return typeof obj == 'function' || false; }; } var isFunction$1 = isFunction; var hasObjectTag = tagTester('Object'); // In IE 10 - Edge 13, `DataView` has string tag `'[object Object]'`. // In IE 11, the most common among them, this problem also applies to // `Map`, `WeakMap` and `Set`. var hasStringTagBug = ( supportsDataView && hasObjectTag(new DataView(new ArrayBuffer(8))) ), isIE11 = (typeof Map !== 'undefined' && hasObjectTag(new Map)); var isDataView = tagTester('DataView'); // In IE 10 - Edge 13, we need a different heuristic // to determine whether an object is a `DataView`. function ie10IsDataView(obj) { return obj != null && isFunction$1(obj.getInt8) && isArrayBuffer(obj.buffer); } var isDataView$1 = (hasStringTagBug ? ie10IsDataView : isDataView); // Is a given value an array? // Delegates to ECMA5's native `Array.isArray`. var isArray = nativeIsArray || tagTester('Array'); // Internal function to check whether `key` is an own property name of `obj`. function has$1(obj, key) { return obj != null && hasOwnProperty.call(obj, key); } var isArguments = tagTester('Arguments'); // Define a fallback version of the method in browsers (ahem, IE < 9), where // there isn't any inspectable "Arguments" type. (function() { if (!isArguments(arguments)) { isArguments = function(obj) { return has$1(obj, 'callee'); }; } }()); var isArguments$1 = isArguments; // Is a given object a finite number? function isFinite$1(obj) { return !isSymbol(obj) && _isFinite(obj) && !isNaN(parseFloat(obj)); } // Is the given value `NaN`? function isNaN$1(obj) { return isNumber(obj) && _isNaN(obj); } // Predicate-generating function. Often useful outside of Underscore. function constant(value) { return function() { return value; }; } // Common internal logic for `isArrayLike` and `isBufferLike`. function createSizePropertyCheck(getSizeProperty) { return function(collection) { var sizeProperty = getSizeProperty(collection); return typeof sizeProperty == 'number' && sizeProperty >= 0 && sizeProperty <= MAX_ARRAY_INDEX; } } // Internal helper to generate a function to obtain property `key` from `obj`. function shallowProperty(key) { return function(obj) { return obj == null ? void 0 : obj[key]; }; } // Internal helper to obtain the `byteLength` property of an object. var getByteLength = shallowProperty('byteLength'); // Internal helper to determine whether we should spend extensive checks against // `ArrayBuffer` et al. var isBufferLike = createSizePropertyCheck(getByteLength); // Is a given value a typed array? var typedArrayPattern = /\[object ((I|Ui)nt(8|16|32)|Float(32|64)|Uint8Clamped|Big(I|Ui)nt64)Array\]/; function isTypedArray(obj) { // `ArrayBuffer.isView` is the most future-proof, so use it when available. // Otherwise, fall back on the above regular expression. return nativeIsView ? (nativeIsView(obj) && !isDataView$1(obj)) : isBufferLike(obj) && typedArrayPattern.test(toString.call(obj)); } var isTypedArray$1 = supportsArrayBuffer ? isTypedArray : constant(false); // Internal helper to obtain the `length` property of an object. var getLength = shallowProperty('length'); // Internal helper to create a simple lookup structure. // `collectNonEnumProps` used to depend on `_.contains`, but this led to // circular imports. `emulatedSet` is a one-off solution that only works for // arrays of strings. function emulatedSet(keys) { var hash = {}; for (var l = keys.length, i = 0; i < l; ++i) hash[keys[i]] = true; return { contains: function(key) { return hash[key]; }, push: function(key) { hash[key] = true; return keys.push(key); } }; } // Internal helper. Checks `keys` for the presence of keys in IE < 9 that won't // be iterated by `for key in ...` and thus missed. Extends `keys` in place if // needed. function collectNonEnumProps(obj, keys) { keys = emulatedSet(keys); var nonEnumIdx = nonEnumerableProps.length; var constructor = obj.constructor; var proto = isFunction$1(constructor) && constructor.prototype || ObjProto; // Constructor is a special case. var prop = 'constructor'; if (has$1(obj, prop) && !keys.contains(prop)) keys.push(prop); while (nonEnumIdx--) { prop = nonEnumerableProps[nonEnumIdx]; if (prop in obj && obj[prop] !== proto[prop] && !keys.contains(prop)) { keys.push(prop); } } } // Retrieve the names of an object's own properties. // Delegates to **ECMAScript 5**'s native `Object.keys`. function keys(obj) { if (!isObject(obj)) return []; if (nativeKeys) return nativeKeys(obj); var keys = []; for (var key in obj) if (has$1(obj, key)) keys.push(key); // Ahem, IE < 9. if (hasEnumBug) collectNonEnumProps(obj, keys); return keys; } // Is a given array, string, or object empty? // An "empty" object has no enumerable own-properties. function isEmpty(obj) { if (obj == null) return true; // Skip the more expensive `toString`-based type checks if `obj` has no // `.length`. var length = getLength(obj); if (typeof length == 'number' && ( isArray(obj) || isString(obj) || isArguments$1(obj) )) return length === 0; return getLength(keys(obj)) === 0; } // Returns whether an object has a given set of `key:value` pairs. function isMatch(object, attrs) { var _keys = keys(attrs), length = _keys.length; if (object == null) return !length; var obj = Object(object); for (var i = 0; i < length; i++) { var key = _keys[i]; if (attrs[key] !== obj[key] || !(key in obj)) return false; } return true; } // If Underscore is called as a function, it returns a wrapped object that can // be used OO-style. This wrapper holds altered versions of all functions added // through `_.mixin`. Wrapped objects may be chained. function _$1(obj) { if (obj instanceof _$1) return obj; if (!(this instanceof _$1)) return new _$1(obj); this._wrapped = obj; } _$1.VERSION = VERSION; // Extracts the result from a wrapped and chained object. _$1.prototype.value = function() { return this._wrapped; }; // Provide unwrapping proxies for some methods used in engine operations // such as arithmetic and JSON stringification. _$1.prototype.valueOf = _$1.prototype.toJSON = _$1.prototype.value; _$1.prototype.toString = function() { return String(this._wrapped); }; // Internal function to wrap or shallow-copy an ArrayBuffer, // typed array or DataView to a new view, reusing the buffer. function toBufferView(bufferSource) { return new Uint8Array( bufferSource.buffer || bufferSource, bufferSource.byteOffset || 0, getByteLength(bufferSource) ); } // We use this string twice, so give it a name for minification. var tagDataView = '[object DataView]'; // Internal recursive comparison function for `_.isEqual`. function eq(a, b, aStack, bStack) { // Identical objects are equal. `0 === -0`, but they aren't identical. // See the [Harmony `egal` proposal](https://wiki.ecmascript.org/doku.php?id=harmony:egal). if (a === b) return a !== 0 || 1 / a === 1 / b; // `null` or `undefined` only equal to itself (strict comparison). if (a == null || b == null) return false; // `NaN`s are equivalent, but non-reflexive. if (a !== a) return b !== b; // Exhaust primitive checks var type = typeof a; if (type !== 'function' && type !== 'object' && typeof b != 'object') return false; return deepEq(a, b, aStack, bStack); } // Internal recursive comparison function for `_.isEqual`. function deepEq(a, b, aStack, bStack) { // Unwrap any wrapped objects. if (a instanceof _$1) a = a._wrapped; if (b instanceof _$1) b = b._wrapped; // Compare `[[Class]]` names. var className = toString.call(a); if (className !== toString.call(b)) return false; // Work around a bug in IE 10 - Edge 13. if (hasStringTagBug && className == '[object Object]' && isDataView$1(a)) { if (!isDataView$1(b)) return false; className = tagDataView; } switch (className) { // These types are compared by value. case '[object RegExp]': // RegExps are coerced to strings for comparison (Note: '' + /a/i === '/a/i') case '[object String]': // Primitives and their corresponding object wrappers are equivalent; thus, `"5"` is // equivalent to `new String("5")`. return '' + a === '' + b; case '[object Number]': // `NaN`s are equivalent, but non-reflexive. // Object(NaN) is equivalent to NaN. if (+a !== +a) return +b !== +b; // An `egal` comparison is performed for other numeric values. return +a === 0 ? 1 / +a === 1 / b : +a === +b; case '[object Date]': case '[object Boolean]': // Coerce dates and booleans to numeric primitive values. Dates are compared by their // millisecond representations. Note that invalid dates with millisecond representations // of `NaN` are not equivalent. return +a === +b; case '[object Symbol]': return SymbolProto.valueOf.call(a) === SymbolProto.valueOf.call(b); case '[object ArrayBuffer]': case tagDataView: // Coerce to typed array so we can fall through. return deepEq(toBufferView(a), toBufferView(b), aStack, bStack); } var areArrays = className === '[object Array]'; if (!areArrays && isTypedArray$1(a)) { var byteLength = getByteLength(a); if (byteLength !== getByteLength(b)) return false; if (a.buffer === b.buffer && a.byteOffset === b.byteOffset) return true; areArrays = true; } if (!areArrays) { if (typeof a != 'object' || typeof b != 'object') return false; // Objects with different constructors are not equivalent, but `Object`s or `Array`s // from different frames are. var aCtor = a.constructor, bCtor = b.constructor; if (aCtor !== bCtor && !(isFunction$1(aCtor) && aCtor instanceof aCtor && isFunction$1(bCtor) && bCtor instanceof bCtor) && ('constructor' in a && 'constructor' in b)) { return false; } } // Assume equality for cyclic structures. The algorithm for detecting cyclic // structures is adapted from ES 5.1 section 15.12.3, abstract operation `JO`. // Initializing stack of traversed objects. // It's done here since we only need them for objects and arrays comparison. aStack = aStack || []; bStack = bStack || []; var length = aStack.length; while (length--) { // Linear search. Performance is inversely proportional to the number of // unique nested structures. if (aStack[length] === a) return bStack[length] === b; } // Add the first object to the stack of traversed objects. aStack.push(a); bStack.push(b); // Recursively compare objects and arrays. if (areArrays) { // Compare array lengths to determine if a deep comparison is necessary. length = a.length; if (length !== b.length) return false; // Deep compare the contents, ignoring non-numeric properties. while (length--) { if (!eq(a[length], b[length], aStack, bStack)) return false; } } else { // Deep compare objects. var _keys = keys(a), key; length = _keys.length; // Ensure that both objects contain the same number of properties before comparing deep equality. if (keys(b).length !== length) return false; while (length--) { // Deep compare each member key = _keys[length]; if (!(has$1(b, key) && eq(a[key], b[key], aStack, bStack))) return false; } } // Remove the first object from the stack of traversed objects. aStack.pop(); bStack.pop(); return true; } // Perform a deep comparison to check if two objects are equal. function isEqual(a, b) { return eq(a, b); } // Retrieve all the enumerable property names of an object. function allKeys(obj) { if (!isObject(obj)) return []; var keys = []; for (var key in obj) keys.push(key); // Ahem, IE < 9. if (hasEnumBug) collectNonEnumProps(obj, keys); return keys; } // Since the regular `Object.prototype.toString` type tests don't work for // some types in IE 11, we use a fingerprinting heuristic instead, based // on the methods. It's not great, but it's the best we got. // The fingerprint method lists are defined below. function ie11fingerprint(methods) { var length = getLength(methods); return function(obj) { if (obj == null) return false; // `Map`, `WeakMap` and `Set` have no enumerable keys. var keys = allKeys(obj); if (getLength(keys)) return false; for (var i = 0; i < length; i++) { if (!isFunction$1(obj[methods[i]])) return false; } // If we are testing against `WeakMap`, we need to ensure that // `obj` doesn't have a `forEach` method in order to distinguish // it from a regular `Map`. return methods !== weakMapMethods || !isFunction$1(obj[forEachName]); }; } // In the interest of compact minification, we write // each string in the fingerprints only once. var forEachName = 'forEach', hasName = 'has', commonInit = ['clear', 'delete'], mapTail = ['get', hasName, 'set']; // `Map`, `WeakMap` and `Set` each have slightly different // combinations of the above sublists. var mapMethods = commonInit.concat(forEachName, mapTail), weakMapMethods = commonInit.concat(mapTail), setMethods = ['add'].concat(commonInit, forEachName, hasName); var isMap = isIE11 ? ie11fingerprint(mapMethods) : tagTester('Map'); var isWeakMap = isIE11 ? ie11fingerprint(weakMapMethods) : tagTester('WeakMap'); var isSet = isIE11 ? ie11fingerprint(setMethods) : tagTester('Set'); var isWeakSet = tagTester('WeakSet'); // Retrieve the values of an object's properties. function values(obj) { var _keys = keys(obj); var length = _keys.length; var values = Array(length); for (var i = 0; i < length; i++) { values[i] = obj[_keys[i]]; } return values; } // Convert an object into a list of `[key, value]` pairs. // The opposite of `_.object` with one argument. function pairs(obj) { var _keys = keys(obj); var length = _keys.length; var pairs = Array(length); for (var i = 0; i < length; i++) { pairs[i] = [_keys[i], obj[_keys[i]]]; } return pairs; } // Invert the keys and values of an object. The values must be serializable. function invert(obj) { var result = {}; var _keys = keys(obj); for (var i = 0, length = _keys.length; i < length; i++) { result[obj[_keys[i]]] = _keys[i]; } return result; } // Return a sorted list of the function names available on the object. function functions(obj) { var names = []; for (var key in obj) { if (isFunction$1(obj[key])) names.push(key); } return names.sort(); } // An internal function for creating assigner functions. function createAssigner(keysFunc, defaults) { return function(obj) { var length = arguments.length; if (defaults) obj = Object(obj); if (length < 2 || obj == null) return obj; for (var index = 1; index < length; index++) { var source = arguments[index], keys = keysFunc(source), l = keys.length; for (var i = 0; i < l; i++) { var key = keys[i]; if (!defaults || obj[key] === void 0) obj[key] = source[key]; } } return obj; }; } // Extend a given object with all the properties in passed-in object(s). var extend = createAssigner(allKeys); // Assigns a given object with all the own properties in the passed-in // object(s). // (https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Object/assign) var extendOwn = createAssigner(keys); // Fill in a given object with default properties. var defaults = createAssigner(allKeys, true); // Create a naked function reference for surrogate-prototype-swapping. function ctor() { return function(){}; } // An internal function for creating a new object that inherits from another. function baseCreate(prototype) { if (!isObject(prototype)) return {}; if (nativeCreate) return nativeCreate(prototype); var Ctor = ctor(); Ctor.prototype = prototype; var result = new Ctor; Ctor.prototype = null; return result; } // Creates an object that inherits from the given prototype object. // If additional properties are provided then they will be added to the // created object. function create(prototype, props) { var result = baseCreate(prototype); if (props) extendOwn(result, props); return result; } // Create a (shallow-cloned) duplicate of an object. function clone(obj) { if (!isObject(obj)) return obj; return isArray(obj) ? obj.slice() : extend({}, obj); } // Invokes `interceptor` with the `obj` and then returns `obj`. // The primary purpose of this method is to "tap into" a method chain, in // order to perform operations on intermediate results within the chain. function tap(obj, interceptor) { interceptor(obj); return obj; } // Normalize a (deep) property `path` to array. // Like `_.iteratee`, this function can be customized. function toPath$1(path) { return isArray(path) ? path : [path]; } _$1.toPath = toPath$1; // Internal wrapper for `_.toPath` to enable minification. // Similar to `cb` for `_.iteratee`. function toPath(path) { return _$1.toPath(path); } // Internal function to obtain a nested property in `obj` along `path`. function deepGet(obj, path) { var length = path.length; for (var i = 0; i < length; i++) { if (obj == null) return void 0; obj = obj[path[i]]; } return length ? obj : void 0; } // Get the value of the (deep) property on `path` from `object`. // If any property in `path` does not exist or if the value is // `undefined`, return `defaultValue` instead. // The `path` is normalized through `_.toPath`. function get(object, path, defaultValue) { var value = deepGet(object, toPath(path)); return isUndefined(value) ? defaultValue : value; } // Shortcut function for checking if an object has a given property directly on // itself (in other words, not on a prototype). Unlike the internal `has` // function, this public version can also traverse nested properties. function has(obj, path) { path = toPath(path); var length = path.length; for (var i = 0; i < length; i++) { var key = path[i]; if (!has$1(obj, key)) return false; obj = obj[key]; } return !!length; } // Keep the identity function around for default iteratees. function identity(value) { return value; } // Returns a predicate for checking whether an object has a given set of // `key:value` pairs. function matcher(attrs) { attrs = extendOwn({}, attrs); return function(obj) { return isMatch(obj, attrs); }; } // Creates a function that, when passed an object, will traverse that object’s // properties down the given `path`, specified as an array of keys or indices. function property(path) { path = toPath(path); return function(obj) { return deepGet(obj, path); }; } // Internal function that returns an efficient (for current engines) version // of the passed-in callback, to be repeatedly applied in other Underscore // functions. function optimizeCb(func, context, argCount) { if (context === void 0) return func; switch (argCount == null ? 3 : argCount) { case 1: return function(value) { return func.call(context, value); }; // The 2-argument case is omitted because we’re not using it. case 3: return function(value, index, collection) { return func.call(context, value, index, collection); }; case 4: return function(accumulator, value, index, collection) { return func.call(context, accumulator, value, index, collection); }; } return function() { return func.apply(context, arguments); }; } // An internal function to generate callbacks that can be applied to each // element in a collection, returning the desired result — either `_.identity`, // an arbitrary callback, a property matcher, or a property accessor. function baseIteratee(value, context, argCount) { if (value == null) return identity; if (isFunction$1(value)) return optimizeCb(value, context, argCount); if (isObject(value) && !isArray(value)) return matcher(value); return property(value); } // External wrapper for our callback generator. Users may customize // `_.iteratee` if they want additional predicate/iteratee shorthand styles. // This abstraction hides the internal-only `argCount` argument. function iteratee(value, context) { return baseIteratee(value, context, Infinity); } _$1.iteratee = iteratee; // The function we call internally to generate a callback. It invokes // `_.iteratee` if overridden, otherwise `baseIteratee`. function cb(value, context, argCount) { if (_$1.iteratee !== iteratee) return _$1.iteratee(value, context); return baseIteratee(value, context, argCount); } // Returns the results of applying the `iteratee` to each element of `obj`. // In contrast to `_.map` it returns an object. function mapObject(obj, iteratee, context) { iteratee = cb(iteratee, context); var _keys = keys(obj), length = _keys.length, results = {}; for (var index = 0; index < length; index++) { var currentKey = _keys[index]; results[currentKey] = iteratee(obj[currentKey], currentKey, obj); } return results; } // Predicate-generating function. Often useful outside of Underscore. function noop(){} // Generates a function for a given object that returns a given property. function propertyOf(obj) { if (obj == null) return noop; return function(path) { return get(obj, path); }; } // Run a function **n** times. function times(n, iteratee, context) { var accum = Array(Math.max(0, n)); iteratee = optimizeCb(iteratee, context, 1); for (var i = 0; i < n; i++) accum[i] = iteratee(i); return accum; } // Return a random integer between `min` and `max` (inclusive). function random(min, max) { if (max == null) { max = min; min = 0; } return min + Math.floor(Math.random() * (max - min + 1)); } // A (possibly faster) way to get the current timestamp as an integer. var now = Date.now || function() { return new Date().getTime(); }; // Internal helper to generate functions for escaping and unescaping strings // to/from HTML interpolation. function createEscaper(map) { var escaper = function(match) { return map[match]; }; // Regexes for identifying a key that needs to be escaped. var source = '(?:' + keys(map).join('|') + ')'; var testRegexp = RegExp(source); var replaceRegexp = RegExp(source, 'g'); return function(string) { string = string == null ? '' : '' + string; return testRegexp.test(string) ? string.replace(replaceRegexp, escaper) : string; }; } // Internal list of HTML entities for escaping. var escapeMap = { '&': '&', '<': '<', '>': '>', '"': '"', "'": ''', '`': '`' }; // Function for escaping strings to HTML interpolation. var _escape = createEscaper(escapeMap); // Internal list of HTML entities for unescaping. var unescapeMap = invert(escapeMap); // Function for unescaping strings from HTML interpolation. var _unescape = createEscaper(unescapeMap); // By default, Underscore uses ERB-style template delimiters. Change the // following template settings to use alternative delimiters. var templateSettings = _$1.templateSettings = { evaluate: /<%([\s\S]+?)%>/g, interpolate: /<%=([\s\S]+?)%>/g, escape: /<%-([\s\S]+?)%>/g }; // When customizing `_.templateSettings`, if you don't want to define an // interpolation, evaluation or escaping regex, we need one that is // guaranteed not to match. var noMatch = /(.)^/; // Certain characters need to be escaped so that they can be put into a // string literal. var escapes = { "'": "'", '\\': '\\', '\r': 'r', '\n': 'n', '\u2028': 'u2028', '\u2029': 'u2029' }; var escapeRegExp = /\\|'|\r|\n|\u2028|\u2029/g; function escapeChar(match) { return '\\' + escapes[match]; } // In order to prevent third-party code injection through // `_.templateSettings.variable`, we test it against the following regular // expression. It is intentionally a bit more liberal than just matching valid // identifiers, but still prevents possible loopholes through defaults or // destructuring assignment. var bareIdentifier = /^\s*(\w|\$)+\s*$/; // JavaScript micro-templating, similar to John Resig's implementation. // Underscore templating handles arbitrary delimiters, preserves whitespace, // and correctly escapes quotes within interpolated code. // NB: `oldSettings` only exists for backwards compatibility. function template(text, settings, oldSettings) { if (!settings && oldSettings) settings = oldSettings; settings = defaults({}, settings, _$1.templateSettings); // Combine delimiters into one regular expression via alternation. var matcher = RegExp([ (settings.escape || noMatch).source, (settings.interpolate || noMatch).source, (settings.evaluate || noMatch).source ].join('|') + '|$', 'g'); // Compile the template source, escaping string literals appropriately. var index = 0; var source = "__p+='"; text.replace(matcher, function(match, escape, interpolate, evaluate, offset) { source += text.slice(index, offset).replace(escapeRegExp, escapeChar); index = offset + match.length; if (escape) { source += "'+\n((__t=(" + escape + "))==null?'':_.escape(__t))+\n'"; } else if (interpolate) { source += "'+\n((__t=(" + interpolate + "))==null?'':__t)+\n'"; } else if (evaluate) { source += "';\n" + evaluate + "\n__p+='"; } // Adobe VMs need the match returned to produce the correct offset. return match; }); source += "';\n"; var argument = settings.variable; if (argument) { // Insure against third-party code injection. (CVE-2021-23358) if (!bareIdentifier.test(argument)) throw new Error( 'variable is not a bare identifier: ' + argument ); } else { // If a variable is not specified, place data values in local scope. source = 'with(obj||{}){\n' + source + '}\n'; argument = 'obj'; } source = "var __t,__p='',__j=Array.prototype.join," + "print=function(){__p+=__j.call(arguments,'');};\n" + source + 'return __p;\n'; var render; try { render = new Function(argument, '_', source); } catch (e) { e.source = source; throw e; } var template = function(data) { return render.call(this, data, _$1); }; // Provide the compiled source as a convenience for precompilation. template.source = 'function(' + argument + '){\n' + source + '}'; return template; } // Traverses the children of `obj` along `path`. If a child is a function, it // is invoked with its parent as context. Returns the value of the final // child, or `fallback` if any child is undefined. function result(obj, path, fallback) { path = toPath(path); var length = path.length; if (!length) { return isFunction$1(fallback) ? fallback.call(obj) : fallback; } for (var i = 0; i < length; i++) { var prop = obj == null ? void 0 : obj[path[i]]; if (prop === void 0) { prop = fallback; i = length; // Ensure we don't continue iterating. } obj = isFunction$1(prop) ? prop.call(obj) : prop; } return obj; } // Generate a unique integer id (unique within the entire client session). // Useful for temporary DOM ids. var idCounter = 0; function uniqueId(prefix) { var id = ++idCounter + ''; return prefix ? prefix + id : id; } // Start chaining a wrapped Underscore object. function chain(obj) { var instance = _$1(obj); instance._chain = true; return instance; } // Internal function to execute `sourceFunc` bound to `context` with optional // `args`. Determines whether to execute a function as a constructor or as a // normal function. function executeBound(sourceFunc, boundFunc, context, callingContext, args) { if (!(callingContext instanceof boundFunc)) return sourceFunc.apply(context, args); var self = baseCreate(sourceFunc.prototype); var result = sourceFunc.apply(self, args); if (isObject(result)) return result; return self; } // Partially apply a function by creating a version that has had some of its // arguments pre-filled, without changing its dynamic `this` context. `_` acts // as a placeholder by default, allowing any combination of arguments to be // pre-filled. Set `_.partial.placeholder` for a custom placeholder argument. var partial = restArguments(function(func, boundArgs) { var placeholder = partial.placeholder; var bound = function() { var position = 0, length = boundArgs.length; var args = Array(length); for (var i = 0; i < length; i++) { args[i] = boundArgs[i] === placeholder ? arguments[position++] : boundArgs[i]; } while (position < arguments.length) args.push(arguments[position++]); return executeBound(func, bound, this, this, args); }; return bound; }); partial.placeholder = _$1; // Create a function bound to a given object (assigning `this`, and arguments, // optionally). var bind = restArguments(function(func, context, args) { if (!isFunction$1(func)) throw new TypeError('Bind must be called on a function'); var bound = restArguments(function(callArgs) { return executeBound(func, bound, context, this, args.concat(callArgs)); }); return bound; }); // Internal helper for collection methods to determine whether a collection // should be iterated as an array or as an object. // Related: https://people.mozilla.org/~jorendorff/es6-draft.html#sec-tolength // Avoids a very nasty iOS 8 JIT bug on ARM-64. #2094 var isArrayLike = createSizePropertyCheck(getLength); // Internal implementation of a recursive `flatten` function. function flatten$1(input, depth, strict, output) { output = output || []; if (!depth && depth !== 0) { depth = Infinity; } else if (depth <= 0) { return output.concat(input); } var idx = output.length; for (var i = 0, length = getLength(input); i < length; i++) { var value = input[i]; if (isArrayLike(value) && (isArray(value) || isArguments$1(value))) { // Flatten current level of array or arguments object. if (depth > 1) { flatten$1(value, depth - 1, strict, output); idx = output.length; } else { var j = 0, len = value.length; while (j < len) output[idx++] = value[j++]; } } else if (!strict) { output[idx++] = value; } } return output; } // Bind a number of an object's methods to that object. Remaining arguments // are the method names to be bound. Useful for ensuring that all callbacks // defined on an object belong to it. var bindAll = restArguments(function(obj, keys) { keys = flatten$1(keys, false, false); var index = keys.length; if (index < 1) throw new Error('bindAll must be passed function names'); while (index--) { var key = keys[index]; obj[key] = bind(obj[key], obj); } return obj; }); // Memoize an expensive function by storing its results. function memoize(func, hasher) { var memoize = function(key) { var cache = memoize.cache; var address = '' + (hasher ? hasher.apply(this, arguments) : key); if (!has$1(cache, address)) cache[address] = func.apply(this, arguments); return cache[address]; }; memoize.cache = {}; return memoize; } // Delays a function for the given number of milliseconds, and then calls // it with the arguments supplied. var delay = restArguments(function(func, wait, args) { return setTimeout(function() { return func.apply(null, args); }, wait); }); // Defers a function, scheduling it to run after the current call stack has // cleared. var defer = partial(delay, _$1, 1); // Returns a function, that, when invoked, will only be triggered at most once // during a given window of time. Normally, the throttled function will run // as much as it can, without ever going more than once per `wait` duration; // but if you'd like to disable the execution on the leading edge, pass // `{leading: false}`. To disable execution on the trailing edge, ditto. function throttle(func, wait, options) { var timeout, context, args, result; var previous = 0; if (!options) options = {}; var later = function() { previous = options.leading === false ? 0 : now(); timeout = null; result = func.apply(context, args); if (!timeout) context = args = null; }; var throttled = function() { var _now = now(); if (!previous && options.leading === false) previous = _now; var remaining = wait - (_now - previous); context = this; args = arguments; if (remaining <= 0 || remaining > wait) { if (timeout) { clearTimeout(timeout); timeout = null; } previous = _now; result = func.apply(context, args); if (!timeout) context = args = null; } else if (!timeout && options.trailing !== false) { timeout = setTimeout(later, remaining); } return result; }; throttled.cancel = function() { clearTimeout(timeout); previous = 0; timeout = context = args = null; }; return throttled; } // When a sequence of calls of the returned function ends, the argument // function is triggered. The end of a sequence is defined by the `wait` // parameter. If `immediate` is passed, the argument function will be // triggered at the beginning of the sequence instead of at the end. function debounce(func, wait, immediate) { var timeout, previous, args, result, context; var later = function() { var passed = now() - previous; if (wait > passed) { timeout = setTimeout(later, wait - passed); } else { timeout = null; if (!immediate) result = func.apply(context, args); // This check is needed because `func` can recursively invoke `debounced`. if (!timeout) args = context = null; } }; var debounced = restArguments(function(_args) { context = this; args = _args; previous = now(); if (!timeout) { timeout = setTimeout(later, wait); if (immediate) result = func.apply(context, args); } return result; }); debounced.cancel = function() { clearTimeout(timeout); timeout = args = context = null; }; return debounced; } // Returns the first function passed as an argument to the second, // allowing you to adjust arguments, run code before and after, and // conditionally execute the original function. function wrap(func, wrapper) { return partial(wrapper, func); } // Returns a negated version of the passed-in predicate. function negate(predicate) { return function() { return !predicate.apply(this, arguments); }; } // Returns a function that is the composition of a list of functions, each // consuming the return value of the function that follows. function compose() { var args = arguments; var start = args.length - 1; return function() { var i = start; var result = args[start].apply(this, arguments); while (i--) result = args[i].call(this, result); return result; }; } // Returns a function that will only be executed on and after the Nth call. function after(times, func) { return function() { if (--times < 1) { return func.apply(this, arguments); } }; } // Returns a function that will only be executed up to (but not including) the // Nth call. function before(times, func) { var memo; return function() { if (--times > 0) { memo = func.apply(this, arguments); } if (times <= 1) func = null; return memo; }; } // Returns a function that will be executed at most one time, no matter how // often you call it. Useful for lazy initialization. var once = partial(before, 2); // Returns the first key on an object that passes a truth test. function findKey(obj, predicate, context) { predicate = cb(predicate, context); var _keys = keys(obj), key; for (var i = 0, length = _keys.length; i < length; i++) { key = _keys[i]; if (predicate(obj[key], key, obj)) return key; } } // Internal function to generate `_.findIndex` and `_.findLastIndex`. function createPredicateIndexFinder(dir) { return function(array, predicate, context) { predicate = cb(predicate, context); var length = getLength(array); var index = dir > 0 ? 0 : length - 1; for (; index >= 0 && index < length; index += dir) { if (predicate(array[index], index, array)) return index; } return -1; }; } // Returns the first index on an array-like that passes a truth test. var findIndex = createPredicateIndexFinder(1); // Returns the last index on an array-like that passes a truth test. var findLastIndex = createPredicateIndexFinder(-1); // Use a comparator function to figure out the smallest index at which // an object should be inserted so as to maintain order. Uses binary search. function sortedIndex(array, obj, iteratee, context) { iteratee = cb(iteratee, context, 1); var value = iteratee(obj); var low = 0, high = getLength(array); while (low < high) { var mid = Math.floor((low + high) / 2); if (iteratee(array[mid]) < value) low = mid + 1; else high = mid; } return low; } // Internal function to generate the `_.indexOf` and `_.lastIndexOf` functions. function createIndexFinder(dir, predicateFind, sortedIndex) { return function(array, item, idx) { var i = 0, length = getLength(array); if (typeof idx == 'number') { if (dir > 0) { i = idx >= 0 ? idx : Math.max(idx + length, i); } else { length = idx >= 0 ? Math.min(idx + 1, length) : idx + length + 1; } } else if (sortedIndex && idx && length) { idx = sortedIndex(array, item); return array[idx] === item ? idx : -1; } if (item !== item) { idx = predicateFind(slice.call(array, i, length), isNaN$1); return idx >= 0 ? idx + i : -1; } for (idx = dir > 0 ? i : length - 1; idx >= 0 && idx < length; idx += dir) { if (array[idx] === item) return idx; } return -1; }; } // Return the position of the first occurrence of an item in an array, // or -1 if the item is not included in the array. // If the array is large and already in sort order, pass `true` // for **isSorted** to use binary search. var indexOf = createIndexFinder(1, findIndex, sortedIndex); // Return the position of the last occurrence of an item in an array, // or -1 if the item is not included in the array. var lastIndexOf = createIndexFinder(-1, findLastIndex); // Return the first value which passes a truth test. function find(obj, predicate, context) { var keyFinder = isArrayLike(obj) ? findIndex : findKey; var key = keyFinder(obj, predicate, context); if (key !== void 0 && key !== -1) return obj[key]; } // Convenience version of a common use case of `_.find`: getting the first // object containing specific `key:value` pairs. function findWhere(obj, attrs) { return find(obj, matcher(attrs)); } // The cornerstone for collection functions, an `each` // implementation, aka `forEach`. // Handles raw objects in addition to array-likes. Treats all // sparse array-likes as if they were dense. function each(obj, iteratee, context) { iteratee = optimizeCb(iteratee, context); var i, length; if (isArrayLike(obj)) { for (i = 0, length = obj.length; i < length; i++) { iteratee(obj[i], i, obj); } } else { var _keys = keys(obj); for (i = 0, length = _keys.length; i < length; i++) { iteratee(obj[_keys[i]], _keys[i], obj); } } return obj; } // Return the results of applying the iteratee to each element. function map(obj, iteratee, context) { iteratee = cb(iteratee, context); var _keys = !isArrayLike(obj) && keys(obj), length = (_keys || obj).length, results = Array(length); for (var index = 0; index < length; index++) { var currentKey = _keys ? _keys[index] : index; results[index] = iteratee(obj[currentKey], currentKey, obj); } return results; } // Internal helper to create a reducing function, iterating left or right. function createReduce(dir) { // Wrap code that reassigns argument variables in a separate function than // the one that accesses `arguments.length` to avoid a perf hit. (#1991) var reducer = function(obj, iteratee, memo, initial) { var _keys = !isArrayLike(obj) && keys(obj), length = (_keys || obj).length, index = dir > 0 ? 0 : length - 1; if (!initial) { memo = obj[_keys ? _keys[index] : index]; index += dir; } for (; index >= 0 && index < length; index += dir) { var currentKey = _keys ? _keys[index] : index; memo = iteratee(memo, obj[currentKey], currentKey, obj); } return memo; }; return function(obj, iteratee, memo, context) { var initial = arguments.length >= 3; return reducer(obj, optimizeCb(iteratee, context, 4), memo, initial); }; } // **Reduce** builds up a single result from a list of values, aka `inject`, // or `foldl`. var reduce = createReduce(1); // The right-associative version of reduce, also known as `foldr`. var reduceRight = createReduce(-1); // Return all the elements that pass a truth test. function filter(obj, predicate, context) { var results = []; predicate = cb(predicate, context); each(obj, function(value, index, list) { if (predicate(value, index, list)) results.push(value); }); return results; } // Return all the elements for which a truth test fails. function reject(obj, predicate, context) { return filter(obj, negate(cb(predicate)), context); } // Determine whether all of the elements pass a truth test. function every(obj, predicate, context) { predicate = cb(predicate, context); var _keys = !isArrayLike(obj) && keys(obj), length = (_keys || obj).length; for (var index = 0; index < length; index++) { var currentKey = _keys ? _keys[index] : index; if (!predicate(obj[currentKey], currentKey, obj)) return false; } return true; } // Determine if at least one element in the object passes a truth test. function some(obj, predicate, context) { predicate = cb(predicate, context); var _keys = !isArrayLike(obj) && keys(obj), length = (_keys || obj).length; for (var index = 0; index < length; index++) { var currentKey = _keys ? _keys[index] : index; if (predicate(obj[currentKey], currentKey, obj)) return true; } return false; } // Determine if the array or object contains a given item (using `===`). function contains(obj, item, fromIndex, guard) { if (!isArrayLike(obj)) obj = values(obj); if (typeof fromIndex != 'number' || guard) fromIndex = 0; return indexOf(obj, item, fromIndex) >= 0; } // Invoke a method (with arguments) on every item in a collection. var invoke = restArguments(function(obj, path, args) { var contextPath, func; if (isFunction$1(path)) { func = path; } else { path = toPath(path); contextPath = path.slice(0, -1); path = path[path.length - 1]; } return map(obj, function(context) { var method = func; if (!method) { if (contextPath && contextPath.length) { context = deepGet(context, contextPath); } if (context == null) return void 0; method = context[path]; } return method == null ? method : method.apply(context, args); }); }); // Convenience version of a common use case of `_.map`: fetching a property. function pluck(obj, key) { return map(obj, property(key)); } // Convenience version of a common use case of `_.filter`: selecting only // objects containing specific `key:value` pairs. function where(obj, attrs) { return filter(obj, matcher(attrs)); } // Return the maximum element (or element-based computation). function max(obj, iteratee, context) { var result = -Infinity, lastComputed = -Infinity, value, computed; if (iteratee == null || typeof iteratee == 'number' && typeof obj[0] != 'object' && obj != null) { obj = isArrayLike(obj) ? obj : values(obj); for (var i = 0, length = obj.length; i < length; i++) { value = obj[i]; if (value != null && value > result) { result = value; } } } else { iteratee = cb(iteratee, context); each(obj, function(v, index, list) { computed = iteratee(v, index, list); if (computed > lastComputed || computed === -Infinity && result === -Infinity) { result = v; lastComputed = computed; } }); } return result; } // Return the minimum element (or element-based computation). function min(obj, iteratee, context) { var result = Infinity, lastComputed = Infinity, value, computed; if (iteratee == null || typeof iteratee == 'number' && typeof obj[0] != 'object' && obj != null) { obj = isArrayLike(obj) ? obj : values(obj); for (var i = 0, length = obj.length; i < length; i++) { value = obj[i]; if (value != null && value < result) { result = value; } } } else { iteratee = cb(iteratee, context); each(obj, function(v, index, list) { computed = iteratee(v, index, list); if (computed < lastComputed || computed === Infinity && result === Infinity) { result = v; lastComputed = computed; } }); } return result; } // Sample **n** random values from a collection using the modern version of the // [Fisher-Yates shuffle](https://en.wikipedia.org/wiki/Fisher–Yates_shuffle). // If **n** is not specified, returns a single random element. // The internal `guard` argument allows it to work with `_.map`. function sample(obj, n, guard) { if (n == null || guard) { if (!isArrayLike(obj)) obj = values(obj); return obj[random(obj.length - 1)]; } var sample = isArrayLike(obj) ? clone(obj) : values(obj); var length = getLength(sample); n = Math.max(Math.min(n, length), 0); var last = length - 1; for (var index = 0; index < n; index++) { var rand = random(index, last); var temp = sample[index]; sample[index] = sample[rand]; sample[rand] = temp; } return sample.slice(0, n); } // Shuffle a collection. function shuffle(obj) { return sample(obj, Infinity); } // Sort the object's values by a criterion produced by an iteratee. function sortBy(obj, iteratee, context) { var index = 0; iteratee = cb(iteratee, context); return pluck(map(obj, function(value, key, list) { return { value: value, index: index++, criteria: iteratee(value, key, list) }; }).sort(function(left, right) { var a = left.criteria; var b = right.criteria; if (a !== b) { if (a > b || a === void 0) return 1; if (a < b || b === void 0) return -1; } return left.index - right.index; }), 'value'); } // An internal function used for aggregate "group by" operations. function group(behavior, partition) { return function(obj, iteratee, context) { var result = partition ? [[], []] : {}; iteratee = cb(iteratee, context); each(obj, function(value, index) { var key = iteratee(value, index, obj); behavior(result, value, key); }); return result; }; } // Groups the object's values by a criterion. Pass either a string attribute // to group by, or a function that returns the criterion. var groupBy = group(function(result, value, key) { if (has$1(result, key)) result[key].push(value); else result[key] = [value]; }); // Indexes the object's values by a criterion, similar to `_.groupBy`, but for // when you know that your index values will be unique. var indexBy = group(function(result, value, key) { result[key] = value; }); // Counts instances of an object that group by a certain criterion. Pass // either a string attribute to count by, or a function that returns the // criterion. var countBy = group(function(result, value, key) { if (has$1(result, key)) result[key]++; else result[key] = 1; }); // Split a collection into two arrays: one whose elements all pass the given // truth test, and one whose elements all do not pass the truth test. var partition = group(function(result, value, pass) { result[pass ? 0 : 1].push(value); }, true); // Safely create a real, live array from anything iterable. var reStrSymbol = /[^\ud800-\udfff]|[\ud800-\udbff][\udc00-\udfff]|[\ud800-\udfff]/g; function toArray(obj) { if (!obj) return []; if (isArray(obj)) return slice.call(obj); if (isString(obj)) { // Keep surrogate pair characters together. return obj.match(reStrSymbol); } if (isArrayLike(obj)) return map(obj, identity); return values(obj); } // Return the number of elements in a collection. function size(obj) { if (obj == null) return 0; return isArrayLike(obj) ? obj.length : keys(obj).length; } // Internal `_.pick` helper function to determine whether `key` is an enumerable // property name of `obj`. function keyInObj(value, key, obj) { return key in obj; } // Return a copy of the object only containing the allowed properties. var pick = restArguments(function(obj, keys) { var result = {}, iteratee = keys[0]; if (obj == null) return result; if (isFunction$1(iteratee)) { if (keys.length > 1) iteratee = optimizeCb(iteratee, keys[1]); keys = allKeys(obj); } else { iteratee = keyInObj; keys = flatten$1(keys, false, false); obj = Object(obj); } for (var i = 0, length = keys.length; i < length; i++) { var key = keys[i]; var value = obj[key]; if (iteratee(value, key, obj)) result[key] = value; } return result; }); // Return a copy of the object without the disallowed properties. var omit = restArguments(function(obj, keys) { var iteratee = keys[0], context; if (isFunction$1(iteratee)) { iteratee = negate(iteratee); if (keys.length > 1) context = keys[1]; } else { keys = map(flatten$1(keys, false, false), String); iteratee = function(value, key) { return !contains(keys, key); }; } return pick(obj, iteratee, context); }); // Returns everything but the last entry of the array. Especially useful on // the arguments object. Passing **n** will return all the values in // the array, excluding the last N. function initial(array, n, guard) { return slice.call(array, 0, Math.max(0, array.length - (n == null || guard ? 1 : n))); } // Get the first element of an array. Passing **n** will return the first N // values in the array. The **guard** check allows it to work with `_.map`. function first(array, n, guard) { if (array == null || array.length < 1) return n == null || guard ? void 0 : []; if (n == null || guard) return array[0]; return initial(array, array.length - n); } // Returns everything but the first entry of the `array`. Especially useful on // the `arguments` object. Passing an **n** will return the rest N values in the // `array`. function rest(array, n, guard) { return slice.call(array, n == null || guard ? 1 : n); } // Get the last element of an array. 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@@ -87,7 +82,7 @@<div itemprop="articleBody"> <section id="mathematics-in-lean"> <h1>Mathematics in Lean<a class="headerlink" href="#mathematics-in-lean" title="Link to this heading"></a></h1> <h1>Mathematics in Lean<a class="headerlink" href="#mathematics-in-lean" title="Permalink to this heading"></a></h1> <div class="toctree-wrapper compound"> <ul> <li class="toctree-l1"><a class="reference internal" href="C01_Introduction.html">1. Introduction</a><ul>
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