Local Open Scope logic.
Instance LS: listspec t_struct_list _tail.
intros.
split; induction l1; intros.
inv H. destruct l2; inv H0. auto.
split. auto. simpl in H2. inv H2.
constructor; auto.
split. inv H. constructor; auto. apply IHl1 in H3.
intuition.
inv H. apply IHl1 in H3. intuition.
simpl. intuition.
simpl. constructor.
destruct H. inv H. auto.
apply IHl1. intuition.
inv H0; auto.
Qed.

Lemma lseg_is_ptr_or_null :
forall  sh c v1 v2 R,
@lseg t_struct_list _tail LS sh (c) v1 v2 * R |-- !!is_pointer_or_null v1 && (@lseg t_struct_list _tail LS sh c v1 v2)  * R.