rewrite functional_prog.SHA_256'_eq; reflexivity.
Qed.

Lemma FOLD_HB_eq: forall l ls, length l = (c + p)%nat ->
Forall (fun x => length x = (c + p)%nat) ls ->
fold_left h (l :: ls) (Vector.to_list iv_v) =
hash_blocks_bits (HMAC_spec_concat.HMAC_Concat.b c p) B h
(Vector.to_list iv_v) (l ++ concat ls).