Module ExtrFacts := GenExtrFacts (Def) (Conseq) (Extr).

Theorem semax_call_backward: forall {CS: compspecs} {Espec: OracleKind} (Delta: tycontext),
forall ret a bl R,
@semax CS Espec Delta
(EX argsig: _, EX retsig: _, EX cc: _,
EX A: _, EX P: _, EX Q: _, EX NEP: _, EX NEQ: _, EX ts: _, EX x: _,
!! (Cop.classify_fun (typeof a) =
Cop.fun_case_f (type_of_params argsig) retsig cc /\
(retsig = Tvoid -> ret = None) /\
tc_fn_return Delta ret retsig) &&
((*|>*)((tc_expr Delta a) && (tc_exprlist Delta (snd (split argsig)) bl)))  &&
`(func_ptr (mk_funspec  (argsig,retsig) cc A P Q NEP NEQ)) (eval_expr a) &&
|>((`(P ts x: environ -> mpred) (make_args' (argsig,retsig) (eval_exprlist (snd (split argsig)) bl))) * oboxopt Delta ret (maybe_retval (Q ts x) retsig ret -* R)))
(Scall ret a bl)
(normal_ret_assert R).