proposition: Lemma Zdiv_mult_cancel_r : forall a b c:Z, c <> 0 -> (a*c)/(b*c) = a/b.
proof: Proof. intros a b c ?. zero_or_not b. apply Z.div_mul_cancel_r; auto. Qed.
imports: ZArith_base Zbool ZArithRing Zcomplements Setoid Morphisms