intros.
hnf; intros.
simpl.
intros.
destruct H2 as [? [? [? [? [? ?]]]]].
contradiction.
Qed.

(* Specifications: *)
Lemma semax_func_cons_ext:
forall (V: varspecs) (G: funspecs) {C: compspecs} fs id ef argsig retsig A P Q NEP NEQ
argsig'
(G': funspecs) cc (ids: list ident),
ids = map fst argsig' -> (* redundant but useful for the client,
to calculate ids by reflexivity *)
argsig' = zip_with_tl ids argsig ->
ef_sig ef =
mksignature
(typlist_of_typelist (type_of_params argsig'))
(opttyp_of_type retsig) cc ->
id_in_list id (map (@fst _ _) fs) = false ->
length ids = length (typelist2list argsig) ->
(forall gx ts x (ret : option val),
(Q ts x (make_ext_rval gx ret)
&& !!has_opttyp ret (opttyp_of_type retsig)
|-- !!tc_option_val retsig ret)) ->
(forall n, semax_external Espec ids ef A P Q n) ->
semax_func V G fs G' ->
semax_func V G ((id, External ef argsig retsig cc)::fs)
((id, mk_funspec (argsig', retsig) cc A P Q NEP NEQ)  :: G').