Instance CompSpecs : compspecs. make_compspecs prog. Defined.
Definition Vprog : varspecs. mk_varspecs prog. Defined.
Definition t_struct_list := Tstruct _list noattr.
Fixpoint listrep (sigma: list int) (x: val) : mpred :=
match sigma with
| h::hs =>
EX y:val,
data_at Tsh t_struct_list (Vint h,y) x  *  listrep hs y
| nil =>
!! (x = nullval) && emp
end.
Arguments listrep sigma x : simpl never.
Hint Resolve listrep_local_facts : saturate_local.

Lemma listrep_valid_pointer:
forall sigma p,
listrep sigma p |-- valid_pointer p.