intros. simpl in |- *. rewrite H. rewrite mult_plus_distr_r. trivial with arith.
Qed.
(****************************************************************)
(* Complements sur Lt Le Gt... *)

(* Specifications: *)
Theorem le_plus_n_m : forall n m : nat, n <= m -> n + n <= m + m.
simple induction n. auto with arith.