Definition field_address t gfs p :=
if (field_compatible_dec t gfs p)
then offset_val (nested_field_offset t gfs) p
else Vundef.
Definition field_address0 t gfs p :=
if (field_compatible0_dec t gfs p)
then offset_val (nested_field_offset t gfs) p
else Vundef.

Lemma gfield_array_type_complete_legal_cosu_type: forall (t: type) lo hi,
legal_field0 t (ArraySubsc lo) ->
complete_legal_cosu_type t = true ->
complete_legal_cosu_type (gfield_array_type t lo hi) = true.