https://ec.europa.eu/commission/sites/beta-political/files/citizens-rights-essential-principles-draft-position-paper_en.pdf
https://www.gov.uk/government/news/david-davis-opening-remarks-at-the-start-of-the-fourth-round-of-eu-exit-negotiations
https://www.iwh-halle.de/fileadmin/user_upload/publications/iwh_discussion_papers/iwh-discussion-paper_2019-04_Brautzsch_Holtemoeller.pdf