(** ** Lemmas about erased values*)

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

Lemma val_erasure_longofwords: forall v1 v1' v2 v2' (Hval_erasure: val_erasure v1 v1') (Hval_erasure: val_erasure v2 v2'), val_erasure (Val.longofwords v1 v2) (Val.longofwords v1' v2').