proposition: Lemma div_mult_compat_l : forall a b c : nat, Divides a b -> Divides a (b * c).
proof: Proof. intros. elim H. intro x. intros. unfold Divides in |- *. rewrite H0. split with (x * c). rewrite mult_assoc. reflexivity. Qed.
imports: ZArith Wf_nat lemmas natZ dec exp