(** ** Lemmas about erased values*)

  Definition isDefined v :=
    match v with
    | Vundef => false
    | _ => true
    end.

Lemma val_erasure_add_result: forall v1 v1' v2 v2' v, val_erasure v1 v1' -> val_erasure v2 v2' -> Val.add v1 v2 = v -> isDefined v -> Val.add v1' v2' = v.