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
$$$a \equiv b \pmod n \land c \equiv d \pmod n \Rightarrow a - c \equiv b - d \pmod n$$$
Lean4
@[gcongr]
protected theorem sub (h₁ : a ≡ b [ZMOD n]) (h₂ : c ≡ d [ZMOD n]) : a - c ≡ b - d [ZMOD n] :=
by
rw [sub_eq_add_neg, sub_eq_add_neg]
exact h₁.add h₂.neg