https://www.euronews.com/2018/09/25/why-is-the-irish-border-issue-so-complex-euronews-answers
https://publications.parliament.uk/pa/cm201719/cmselect/cmintrade/520/520.pdf
https://www.chba.org.uk/for-members/library/overseas-seminars/the-status-of-gibraltar-under-eu-law
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/680366/Technical_Note_-_International_Agreements_in_the_Implementation_Period_-_CLEAN.pdf