English
Let a, b, n be integers. Then a ≡ b (mod n) iff there exists t ∈ ℤ such that b = a + n t.
Русский
Пусть a, b, n — целые числа. Тогда a ≡ b (mod n) эквивалентно существованию t ∈ ℤ such that b = a + n t.
LaTeX
$$$a \equiv b \pmod n \iff \exists t \in \mathbb{Z}, \; b = a + n t$$$
Lean4
theorem modEq_iff_add_fac {a b n : ℤ} : a ≡ b [ZMOD n] ↔ ∃ t, b = a + n * t :=
by
rw [modEq_iff_dvd]
exact exists_congr fun t => sub_eq_iff_eq_add'