Definition lseg_cons_right (ls: listspec list_structid list_link list_token)
dsh psh (l: list (val * elemtype ls)) (x z: val) : mpred :=
!! (~ ptr_eq x z) &&
EX h:(elemtype ls), EX r:list (val * elemtype ls), EX y:val,
!!(l=r++(y,h)::nil /\ is_pointer_or_null y)  &&
list_token dsh y * list_cell ls dsh h y *
field_at psh list_struct (StructField list_link :: nil) (valinject (nested_field_type list_struct (StructField list_link :: nil)) z) y *
lseg ls dsh psh r x y.

Lemma lseg_cons_right_null (ls: listspec list_structid list_link list_token): forall dsh psh l x h y,
list_token dsh y * list_cell ls dsh h y * field_at psh list_struct (StructField list_link :: nil) (valinject (nested_field_type list_struct (StructField list_link :: nil)) nullval) y *
lseg ls dsh psh l x y
|--   lseg ls dsh psh (l++(y,h)::nil) x nullval.