Proof with eauto with val_renamings.
intros v v' v'' f f' f'' Hval'' Hval' Hf.
inversion Hval'; subst; inversion Hval''; subst...
Qed.

Lemma val_obs_list_trans:
forall (vs vs' vs'' : seq val) (f f' f'' : memren),
val_obs_list f vs vs'' ->
val_obs_list f' vs vs' ->
(forall b b' b'' : block,
f b = Some b'' ->
f' b = Some b' ->
f'' b' = Some b'') ->
val_obs_list f'' vs' vs''.