Definition modu (v w: aval) :=
  match w, v with
  | I i2, I i1 =>
      if Int.eq i2 Int.zero
      then if va_strict tt then Vbot else ntop
      else I (Int.modu i1 i2)
  | I i2, _ => uns (provenance v) (usize i2)
  | _, _ => ntop2 v w
  end.

(* Specifications: *)
Lemma modu_sound: forall v w u x y, vmatch v x -> vmatch w y -> Val.modu v w = Some u -> vmatch u (modu x y).