Module Proof3.  (*************** inductive lseg *******************)
Fixpoint lseg (sh: share)
(contents: list val) (x z: val) : mpred :=
match contents with
| h::hs => !! (x<>z) &&
EX y:val,
data_at sh t_struct_list (h,y) x * lseg sh hs y z
| nil => !! (x = z /\ is_pointer_or_null x) && emp
end.
Arguments lseg sh contents x z : simpl never.

(* Specifications: *)
Lemma lseg_local_facts:
forall sh contents p q,
lseg sh contents p q |--
!! (is_pointer_or_null p /\ is_pointer_or_null q /\ (p=q <-> contents=nil)).