Definition poffset (p: aptr) : aptr :=
  match p with
  | Gl id ofs => Glo id
  | Stk ofs => Stack
  | _ => p
  end.

(* Specifications: *)
Lemma poffset_sound: forall b ofs1 ofs2 p, pmatch b ofs1 p -> pmatch b ofs2 (poffset p).