apply Rle_ge;apply Ropp_le_contravar; auto with real.
rewrite Ropp_0; auto with real.
Qed.

Theorem Rge_sign_neg_pos: forall x y: R, (0 >= x -> y >= 0  -> 0>= x * y)%R.
intros; apply Rle_ge; apply Rle_sign_neg_pos; auto with real.