proposition: Lemma Rmult_neg_pos : forall r1 r2, r1 < 0 -> r2 > 0 -> r1 * r2 < 0.
proof: Proof. intros r1 r2 H1 H2. now rewrite <-(Rmult_0_r r1); apply Rmult_lt_gt_compat_neg_l. Qed.
imports: RelationClasses Raxioms Rpow_def ZArith ZArithRing RealField