End GET_CO.

Lemma co_sizeof_get_co_change_composite {cs_from cs_to} {CCE: change_composite_env cs_from cs_to}: forall id,
match (coeq cs_from cs_to) ! id with
| Some b => test_aux cs_from cs_to b id
| None => false
end = true ->
co_sizeof (@get_co cs_from id) = co_sizeof (@get_co cs_to id).