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 val_inject_flat: forall m1 m2 j (Inj: Mem.inject j m1 m2) v1 v2 (V: val_inject j v1 v2), val_inject (Mem.flat_inj (Mem.nextblock m1)) v1 v1.