https://www.elibrary.imf.org/downloadpdf/book/9798400224119/CH004.xml
https://www.bloomberg.com/news/articles/2019-09-11/world-s-oldest-customs-union-and-u-k-reach-a-post-brexit-deal
https://home.kpmg.com/content/dam/kpmg/nl/pdf/2018/sector/overheid/impact-van-non-tarifaire-handelsbelemmeringen-als-gevolg-van-brexit.pdf
https://www.econstor.eu/bitstream/10419/266146/1/1820832732.pdf