simpl in |- *; auto.
intros n Hrec m; case m; clear m.
intros Hle; inversion Hle.
intros m' Hle; simpl in |- *; apply Hrec; auto with arith.
Qed.

(* Specifications: *)
Theorem minus_le : forall m n : nat, m - n <= m.
intros m; elim m.