https://www.sbs.strath.ac.uk/economics/fraser/20170322/FEC-Vol41-No1.pdf
https://www.politico.eu/article/eu-warn-financial-risk-andorra-monaco-san-marino/
https://www.greatbritishpolitics.co.uk/europe/654-dual-nationality-and-the-hurdles-facing-britons-who-want-to-keep-eu-citizenship-after-brexit.html
https://documents-dds-ny.un.org/doc/UNDOC/LTD/N22/622/29/PDF/N2262229.pdf?OpenElement