https://blogs.lse.ac.uk/brexit/2019/04/15/brexit-lessons-from-the-silesian-backstop-of-1919-25/
http://www.cer.org.uk/sites/default/files/insight_JS_9.5.17.pdf
http://fedtrust.co.uk/mrs-may-in-florence/
https://www.opendemocracy.net/en/opendemocracyuk/customs-union-leaves-everything-play-trade-justice/?utm_source=Daily+Newsletter&utm_campaign=f531c721c4-DAILY_NEWSLETTER_MAILCHIMP&utm_medium=email&utm_term=0_717bc5d86d-f531c721c4-407405485