intros.
destruct (Req_ne_dec a 0%R)...
destruct (Req_ne_dec b 0%R).
right...
elimtype False.
apply (prod_neq_R0 a b)...
Qed.

(* Specifications: *)
Lemma Req_le_trans x y z: x = y -> y <= z -> x <= z.
Lemma Rdiv_le_1 a b: 0 < a -> a <= b -> 1 <= b / a.
Proof with auto with real.