Definition binop_long (sem: int64 -> int64 -> int64) (x y: aval) :=
  match x, y with L n, L m => L (sem n m) | _, _ => ntop2 x y end.

Lemma binop_long_sound: forall sem v x w y, vmatch v x -> vmatch w y -> vmatch (match v, w with Vlong i, Vlong j => Vlong(sem i j) | _, _ => Vundef end) (binop_long sem x y).