Hint Resolve lseg_valid_pointer : valid_pointer.

Lemma lseg_cons': forall sh (v u x a b: val) ,
readable_share sh ->
data_at sh t_struct_list (v, u) x * data_at sh t_struct_list (a,b) u
|-- lseg sh [v] x u * data_at sh t_struct_list (a,b) u.