Hint Resolve lseg_valid_pointer : valid_pointer.

Lemma lseg_app': forall sh s1 s2 (a w x y z: val),
readable_share sh ->
lseg sh s1 w x * lseg sh s2 x y * data_at sh t_struct_list (a,z) y |--
lseg sh (s1++s2) w y * data_at sh t_struct_list (a,z) y.