red;apply Ropp_lt_contravar; auto with real.
rewrite Ropp_0; auto with real.
Qed.

(* Specifications: *)
Theorem Rgt_sign_neg_pos: forall x y, (0 > x -> y > 0  -> 0> x * y)%R.
intros; red; apply Rlt_sign_neg_pos; auto with real.
Theorem Rgt_sign_neg_pos: forall x y, (0 > x -> y > 0  -> 0> x * y)%R.
intros; red; apply Rlt_sign_neg_pos; auto with real.