proposition: Theorem lt_mul_m1_neg : forall n m, 1 < n -> m < 0 -> n * m < -1.
proof: Proof. intros n m H1 H2. apply (mul_lt_mono_neg_r m) in H1. - rewrite mul_1_l in H1. now apply lt_m1_r with m. - assumption. Qed.
imports: ZAddOrder