(****************)
simple induction v. intros. rewrite strip_nil. rewrite strip_nil. trivial with arith.
simple induction i. intro. simpl in |- *. rewrite strip_O. trivial with arith.
simple induction j. rewrite strip_O. elim plus_n_O. trivial with arith.
intros. rewrite strip_cons_S. simpl in |- *. rewrite strip_cons_S. apply H.
Qed. Hint Resolve strip_strip.
(****************************************************************)
(* lemmes sur trunc et strip ensembles *)

Lemma app_trunc_strip :
forall (v : list A) (i : nat),
trunc v i ++ strip v i = v.