Hidden resource: how to add one?

hi all
I am trying to make an export_descr_building.txt file for my campaing using 1.1 RTW and the Greek mod ...
I am trying to implement "hidden resources" for Athens and Corinth (specific hoplites) just as Sparta had...

So far, I added in export_descr_building.txt :
hidden_resources sparta, athens, corinth
at the beginning of the file ...

and :
recruit "athenian hoplite" 0 requires factions { greek_cities, } and hidden_resource athens
to allow building of athenian hoplites in athens...
but it doesnt work !
can you help me ?
thx in advance! ~:)