Definition Qmult_resp_Qlt_pos_l:= Qlt_Qmult_cancel_l: forall t x y : Q, Zero < t -> t * x < t * y -> x < y.

Lemma Qmult_Qle_compat: forall n m p q : Q, n <= p -> m <= q -> Zero <= n -> Zero <= m -> n * m <= p * q.