Definition ptr_eq (v1 v2: val) : Prop :=
      match v1,v2 with
      | Vint n1, Vint n2 =>  Archi.ptr64 = false /\ Int.cmpu Ceq n1 n2 = true  /\ Int.cmpu Ceq n1 (Int.repr 0) = true
      | Vlong n1, Vlong n2 =>  Archi.ptr64 = true /\ Int64.cmpu Ceq n1 n2 = true  /\ Int64.cmpu Ceq n1 (Int64.repr 0) = true
      | Vptr b1 ofs1,  Vptr b2 ofs2  =>
            b1=b2 /\ Ptrofs.cmpu Ceq ofs1 ofs2 = true
      | _,_ => False
      end.Definition ptr_neq (v1 v2: val) := ~ ptr_eq v1 v2.

Lemma ptr_eq_sym: forall x y, ptr_eq x y -> ptr_eq y x.