Definition val_inject_opt (j: meminj) (v1 v2: option val) :=
  match v1, v2 with Some v1', Some v2' => val_inject j v1' v2'
  | None, None => True
  | _, _ => False
  end.

Lemma extends_loc_out_of_reach: forall m1 m2 (Ext: Mem.extends m1 m2) b ofs j (Hj: loc_out_of_reach j m2 b ofs), loc_out_of_reach j m1 b ofs.