induction ls; intuition.
unfold compFold.
intuition.
unfold compFold.
fold compFold.
unfold foldBody_option.
comp_simp.
eapply IHls.
Qed.

Lemma Bvector_ne_exists :
forall (n : nat)(v : Bvector n),
n > 0 ->
exists v', v <> v'.