English
If a ≡ b (mod m), then gcd(a,m) = gcd(b,m).
Русский
Если a ≡ b (mod m), то gcd(a,m) = gcd(b,m).
LaTeX
$$$ a \equiv b \pmod{m} \Rightarrow \gcd(a,m) = \gcd(b,m) $$$
Lean4
theorem gcd_eq (h : a ≡ b [MOD m]) : gcd a m = gcd b m :=
by
have h1 := gcd_dvd_right a m
have h2 := gcd_dvd_right b m
exact
dvd_antisymm (dvd_gcd ((h.dvd_iff h1).mp (gcd_dvd_left a m)) h1)
(dvd_gcd ((h.dvd_iff h2).mpr (gcd_dvd_left b m)) h2)