https://blogs.lse.ac.uk/europpblog/2023/04/13/ever-closer-union-and-the-philosophical-history-of-europe/
https://www.diw.de/documents/publikationen/73/diw_01.c.578096.de/18-7-3.pdf
http://www.ebrd.com/cs/Satellite?c=Content&cid=1395272118012&d=&pagename=EBRD%2FContent%2FDownloadDocument