Definition binop_single (sem: float32 -> float32 -> float32) (x y: aval) :=
  match x, y with FS n, FS m => FS (sem n m) | _, _ => ntop2 x y end.

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