Proof with eauto with val_renamings.
intros; destruct v; inversion Hval_obs; subst; simpl...
Qed.

Lemma val_obs_intoffloat:
forall f v v'
(Hval_obs: val_obs f v v'),
val_obs f (Val.maketotal (Val.intoffloat v))
(Val.maketotal (Val.intoffloat v')).