http://library.fes.de/pdf-files/bueros/budapest/15322-20190505.pdf
http://www.euronews.com/2017/09/19/portugal-in-cash-for-passports-scandal?utm_source=newsletter&utm_medium=en&utm_content=portugal-in-cash-for-passports-scandal&_ope=eyJndWlkIjoiZjU3Y2JhYmUwMGUxZDFiNTUxOTU1ZDljNzExNTI1MmEifQ==
http://fedtrust.co.uk/views-from-the-federal-trust/free-movement-and-migration/
http://www.cesifo-group.de/ifoHome/publications/working-papers/CESifoWP/CESifoWPdetails?wp_num=6452&CESifoWP.search=+