Hint Resolve legal_nested_field0_field.

Lemma gfield_array_offset_in_range: forall t lo hi,
legal_field0 t (ArraySubsc lo) ->
legal_field0 t (ArraySubsc hi) ->
complete_legal_cosu_type t = true ->
0 <= gfield_offset t (ArraySubsc lo) /\
gfield_offset t (ArraySubsc lo) + sizeof (gfield_array_type t lo hi) <= sizeof t.