Definition weak_mapsto_ sh e rho :=
match (eval_expr e rho) with
| Vptr b o => (mapsto_ sh (typeof e) (Vptr b o)) ||
(mapsto_ sh (typeof e) (Vptr b o))
| _ => FF
end.

Lemma eval_cast_Vundef:
forall t1 t2, eval_cast t1 t2 Vundef = Vundef.