Fixpoint WcontI (xs: list int) (j:nat) (l:list val):Prop :=
   match j with O => Zlength l = 16
   | (S n) => Zlength l = 16 /\
              exists t0 t1 t2 t3,
              Znth ((5 * (Z.of_nat n) + 4 * 0) mod 16) (map Vint xs) = Vint t0 /\
              Znth ((5 * (Z.of_nat n) + 4 * 1) mod 16) (map Vint xs) = Vint t1 /\
              Znth ((5 * (Z.of_nat n) + 4 * 2) mod 16) (map Vint xs) = Vint t2 /\
              Znth ((5 * (Z.of_nat n) + 4 * 3) mod 16) (map Vint xs) = Vint t3 /\
              exists wl, WcontI xs n wl /\
                match Wcopyspec t0 t1 t2 t3 with
                 (s0,s1,s2,s3) => wlistJ' wl (Z.of_nat n) s0 s1 s2 s3 l
                end
  end.

Lemma WcontI_Zlength xs j l: WcontI xs j l -> Zlength l=16.