proposition: Lemma Zmod_plus_compat_lft : forall m a b : Z, (m > 0)%Z -> ((a + b) mod m)%Z = ((a mod m + b) mod m)%Z.
proof: Proof. intros m a b Hm. rewrite (Zplus_comm a b). rewrite (Zplus_comm (a mod m) b). apply Zmod_plus_compat_rht. auto. Qed.
imports: CoRN.model.Zmod.ZGcd