intros. rewrite lseg_unroll by auto.
apply pred_ext. apply orp_left; auto.
rewrite andp_assoc.
do 2 (apply derives_extract_prop; intro).
congruence.
apply orp_right2. auto.
Qed.

Lemma lseg_nil_eq (ls: listspec list_structid list_link list_token):
forall dsh psh p q,
lseg ls dsh psh nil p q = !! (ptr_eq p q) && emp.