http://fedtrust.co.uk/views-from-the-federal-trust/free-movement-and-migration/
http://www.acea.be/uploads/publications/ACEA_position_paper-Brexit.pdf
https://www.euronews.com/2018/09/25/why-is-the-irish-border-issue-so-complex-euronews-answers
https://www.instituteforgovernment.org.uk/sites/default/files/publications/voting-on-brexit-report-final.pdf