Proof with eauto with val_renamings.
intros.
destruct v...
destruct Hvalid as [b' Hf].
specialize (Hid _ _ Hf);
subst...
Qed.

Lemma memval_obs_eq_id:
forall f mv
(Hvalid: valid_memval f mv)
(Hid: forall b b', f b = Some b' -> b = b'),
memval_obs_eq f mv mv.