import Mathlib
-- https://lean-lang.org/doc/reference/latest//The--grind--tactic/#grind
example (n : ℕ) (h : n > 5) : ∃ a b, 3 * a + 4 * b = n := by
use (n - (n % 3) * 4) / 3, n % 3
grind
example (n x y : ℕ) (h : n > x * y - x - y) (hp : gcd x y = 1) : ∃ a b, a * x + b * y = n := by
use (n - (n % x) * y) / x, n % x
grind