Definition substopt {A} (ret: option ident) (v: val) (P: environ -> A)  : environ -> A :=
match ret with
| Some id => subst id v P
| None => P
end.

Lemma smaller_temps_exists : forall l l1 te id i t,
bind_parameter_temps l l1 (PTree.set id Vundef t)=  Some te ->
i <> id ->
exists te', (bind_parameter_temps l l1 t = Some te' /\ te' ! i = te ! i).