https://www.gov.uk/guidance/status-of-eu-nationals-in-the-uk-what-you-need-to-know
http://www.bertelsmann-stiftung.de/fileadmin/files/Projekte/Migration_fair_gestalten/IB_Study_MixedMigration2017_ENG.pdf
http://www.guengl.eu/news/article/gue-ngl-news/adoption-of-the-european-travel-information-and-authorisation-system-a-hidd