(************)
rewrite trunc_all. rewrite rev_rev. trivial with arith.
Qed. Hint Resolve strip_O.

(* Specifications: *)
Lemma strip_app :
forall (v1 v2 : list A) (i : nat),
strip (v1 ++ v2) i = strip v1 i ++ strip v2 (i - length v1).