induction v; intuition; simpl.
auto.
eapply in_or_app; intuition.
destruct h.
left.
eapply in_map; eauto.
right.
eapply in_map; eauto.
Qed.

Lemma vector_tl_eq : forall (A : Set)(n : nat)(v1 v2 : Vector.t A (S n)),
v1 = v2 ->
Vector.tl v1 = Vector.tl v2.