English
If m and n are associated, then for every k we have gcd(m,k) = gcd(n,k).
Русский
Если m ассоциировано с n, то для любого k выполняется gcd(m,k) = gcd(n,k).
LaTeX
$$$\\forall k : \\alpha, \\text{Associated}(m,n) \\Rightarrow \\gcd m k = \\gcd n k$$$
Lean4
theorem gcd_eq_left [NormalizedGCDMonoid α] {m n : α} (h : Associated m n) (k : α) : gcd m k = gcd n k :=
dvd_antisymm_of_normalize_eq (normalize_gcd _ _) (normalize_gcd _ _) (gcd_dvd_gcd h.dvd dvd_rfl)
(gcd_dvd_gcd h.symm.dvd dvd_rfl)