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.

Lemma field_at_Tint: forall t nf v1 v2 p,
nested_field_type t nf = Tint ->
JMeq v1 v2 ->
field_at t nf v1 p = mapsto (field_address t nf p) v2.