Proof with eauto with val_erasure.
intros.
destruct v, chunk; simpl; unfold inj_value; simpl;
repeat econstructor...
Qed.

Lemma val_erasure_longofintu:
forall v v'
(Hval_erasure: val_erasure v v'),
val_erasure (Val.longofintu v) (Val.longofintu v').