repeat rewrite app_length. repeat rewrite  QuadWR_length. reflexivity. Qed.

(* Specifications: *)
Lemma SixteenWR_zlength s: Zlength (SixteenWordRep s) = 16.
rewrite Zlength_correct, SixteenWR_length. trivial. Qed.
Lemma QuadWR_int q i: (0<=i<4)%nat -> exists ii, nth i (QuadWordRep q) Vundef = Vint ii.
intros. destruct q as [[[? ?] ?] ?]. simpl.