
https://theconversation.com/catalan-euskera-y-gallego-futuras-lenguas-oficiales-de-la-ue-213136

https://www.eurofound.europa.eu/sites/default/files/ef_publication/field_ef_document/ef1733en.pdf

http://www.cesifo-group.de/ifoHome/publications/working-papers/CESifoWP/CESifoWPdetails?wp_num=6452&CESifoWP.search=+