https://ec.europa.eu/commission/publications/position-paper-essential-principles-citizens-rights_en
https://blogs.lse.ac.uk/brexit/2019/10/15/the-curve-of-inequality-and-the-brexit-way/
http://www2.warwick.ac.uk/fac/soc/pais/research/researchcentres/irs/crossingthemed/ctm_final_report_4may2017.pdf
https://www.socialeurope.eu/romania-and-bulgaria-stuck-in-eus-second-tier