Definition field_at (t: type) (nf: list ident) (v: reptype (nested_field_type t nf)) (p: val) : Pred := data_at_rec (nested_field_type t nf) v (offset_val (nested_field_offset t nf) p).
Definition data_at (t: type) (v: reptype t) (p: val) : Pred := field_at t nil v p.
Definition field_address (t: type) (nf: list ident) (p: val) : val := offset_val (nested_field_offset t nf) p.
(* Ramification Premises for Nested Load/Store Rule *)

Lemma RP_field: forall t nf u v p,
legal_nested_field t nf ->
legal_type t ->
data_at t u p |-- field_at t nf (proj_reptype t nf u) p *
(field_at t nf v p -* data_at t (upd_reptype t nf u v) p).