https://blogs.lse.ac.uk/brexit/2019/04/15/brexit-lessons-from-the-silesian-backstop-of-1919-25/
https://www.gov.uk/government/news/pms-european-council-press-statement-20-october-2017
http://voxeu.org/system/files/epublication/Brexit_Beckons_VoxEU.pdf