(**************)
simple induction v. intros. rewrite strip_nil. rewrite strip_nil. trivial with arith.
simple induction i. intro. rewrite strip_O. rewrite strip_O. trivial with arith.
simple induction j. rewrite strip_O. rewrite strip_O. try trivial with arith.
intros. rewrite strip_cons_S. rewrite strip_cons_S.
replace (strip (strip l n) (S n0)) with (strip (strip l (S n)) n0).
apply H. apply strip_strip_S.
Qed.

Lemma strip_eq :
forall (v1 v2 : list A) (i : nat), v1 = v2 -> strip v1 i = strip v2 i.