English
If a ≡ b (mod n) and c ≡ d (mod n), then a + c ≡ b + d (mod n).
Русский
Если a ≡ b (mod n) и c ≡ d (mod n), то a + c ≡ b + d (mod n).
LaTeX
$$$a \equiv b \pmod n \quad\text{и}\quad c \equiv d \pmod n \Rightarrow a + c \equiv b + d \pmod n$$$
Lean4
@[gcongr]
protected theorem add (h₁ : a ≡ b [ZMOD n]) (h₂ : c ≡ d [ZMOD n]) : a + c ≡ b + d [ZMOD n] :=
modEq_iff_dvd.2 <| by convert Int.dvd_add h₁.dvd h₂.dvd using 1; cutsat