Definition and (v w: aval) :=
  match v, w with
  | I i1, I i2 => I (Int.and i1 i2)
  | I i, Uns p n | Uns p n, I i => uns p (Z.min n (usize i))
  | I i, x | x, I i => uns (provenance x) (usize i)
  | Uns p1 n1, Uns p2 n2 => uns (plub p1 p2) (Z.min n1 n2)
  | Uns p n, _ => uns (plub p (provenance w)) n
  | _, Uns p n => uns (plub (provenance v) p) n
  | Sgn p1 n1, Sgn p2 n2 => sgn (plub p1 p2) (Z.max n1 n2)
  | _, _ => ntop2 v w
  end.

(* Specifications: *)
Lemma and_sound: forall v w x y, vmatch v x -> vmatch w y -> vmatch (Val.and v w) (and x y).