Hint Resolve Znth_land_is_int.

(* Specifications: *)
Lemma Xarray_simpl:
forall b, length b = 16%nat -> Xarray b 16 = b.
Lemma length_Xarray:
forall b i, length (Xarray b i) = 16%nat.
Lemma nth_Xarray:
forall b i k,
(0 <= k < 16)%Z ->
nthi (Xarray b i) k = W (nthi b) (Z.of_nat i - 16 + (k- Z.of_nat i) mod 16)%Z .
Lemma extract_from_b:
forall b i n,
length b = 16%nat ->
16 <= i < 64 ->
(0 <= n < 16)%Z ->
nthi (Xarray b i) ((Z.of_nat i + n) mod 16) = W (nthi b) (Z.of_nat i - 16 + n).