Definition hashblocks: list int -> list int -> list int:= SHA256.hash_blocks.Definition d := 16%nat.Definition HBS_eq : forall r msg : list int,
         hashblocks r msg =
         match msg with
         | List.nil => r
         | _ :: _ => hashblocks (hashblock r (firstn d msg)) (skipn d msg)
         end := SHA256.hash_blocks_equation.

(* Specifications: *)
Lemma D: (d * 32)%nat = b.