
https://www.un.org/esa/population/publications/migration/migration.htm

https://www.economiesuisse.ch/de/artikel/kuendigungsinitiative-ii-eine-wohlstandsbremse-par-excellence

https://www.greatbritishpolitics.co.uk/europe/654-dual-nationality-and-the-hurdles-facing-britons-who-want-to-keep-eu-citizenship-after-brexit.html