Definition binop_int (sem: int -> int -> int) (x y: aval) :=
  match x, y with I n, I m => I (sem n m) | _, _ => ntop2 x y end.

(* Specifications: *)
Lemma binop_int_sound: forall sem v x w y, vmatch v x -> vmatch w y -> vmatch (match v, w with Vint i, Vint j => Vint(sem i j) | _, _ => Vundef end) (binop_int sem x y).