https://socialeurope.eu/brexit-why-does-northern-ireland-matter-so-much
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/640485/Technical_note_on_Functionality_and_Protocol_7.pdf
http://www.consilium.europa.eu//media/32504/xt21004-ad01re02en18.pdf
https://www.global-counsel.co.uk/sites/default/files/special-reports/downloads/Global%20Counsel_Impact_of_Brexit.pdf