(* Ugly tacty to resolve sign condition for R *)
Require Export RGroundTac.
(* Theorems to simplify the goal 0 ? x * y and x * y ? 0 where ? is < > <= >= *)
intros x y H; apply Rmult_le_pos; auto with real.
Qed.

Theorem Rle_sign_neg_neg: forall x y, (x <= 0 -> y <= 0  -> 0 <= x * y)%R.