Definition rol (x: nval) (amount: int) :=
  match x with
  | Nothing => Nothing
  | I m => I (Int.ror m amount)
  | All => All
  end.

Lemma rol_sound: forall v w x n, vagree v w (rol x n) -> vagree (Val.rol v (Vint n)) (Val.rol w (Vint n)) x.