(* KE EP TOGETHER> *)

(* <KE EP TOGETHER - s'_i_eq *)
Lemma s'_i_eq : _Z s'_i = x' mod 2 ^ w - x' mod 2 ^ p.
unfold s'_i. rewrite Z_from_multp2. fold p. rewrite s_i_eq. rewrite Zmult_comm. rewrite modred.