proposition: Lemma Zmodml: forall a b n, 0 < n -> (a mod n * b) mod n = (a * b) mod n.
proof: Proof. intros a b n H. rewrite Zmult_mod; auto. rewrite Zmod_mod; auto. apply sym_equal; apply Zmult_mod; auto. Qed.
imports: ZArith Znumtheory