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

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