Proof with eauto with val_renamings.
intros.
destruct v1, v1'; inversion Hval_obs;
inversion Hval_obs'; subst; simpl...
Qed.

Lemma val_obs_divu_id:
forall f v1 v2 v,
Val.divu v1 v2 = Some v ->
val_obs f v v.