(* Ugly tacty to resolve sign condition for N *)
Require Export NGroundTac.
Open Scope N_scope.
intros n m p H1 H2; apply Nlt_lt; repeat rewrite N2Nat.inj_mul.
apply mult_lt_compat_l; apply lt_Nlt; repeat rewrite N2Nat.id; auto.
Qed.

Theorem Nmult_le_compat_l: forall n m p, n <= m -> p * n <= p * m.