(********************)
simple induction v. unfold strip in |- *. simpl in |- *. trivial with arith.
intros. elim i. rewrite trunc_O. rewrite strip_O. simpl in |- *. trivial with arith.
intros. unfold strip in |- *. simpl in |- *.
rewrite trunc_app. rewrite rev_app. rewrite length_rev.
case n. rewrite <- minus_n_O.
rewrite <- minus_n_n. rewrite trunc_O. rewrite trunc_O. simpl in |- *.
rewrite <- length_rev. rewrite trunc_all. rewrite rev_rev. trivial with arith.
intro. replace (length l - S n0 - length l) with 0.
rewrite trunc_O. simpl in |- *.
replace (rev A (trunc (rev A l) (length l - S n0))) with (strip l (S n0)).
rewrite H. trivial with arith.
unfold strip in |- *. trivial with arith.
rewrite minus_minus_lem1. trivial with arith.
Qed.

Lemma strip_trunc_i :
forall (v : list A) (i : nat), strip (trunc v i) i = nil.