
https://blogs.lse.ac.uk/europpblog/2021/10/22/de-facto-differentiation-in-action-why-poland-will-stay-in-the-eu-with-or-without-the-blessing-of-brussels/

https://www.socialeurope.eu/the-frugal-four-should-save-the-european-project

http://www.etui.org/Publications2/Books/Innovative-union-practices-in-Central-Eastern-Europe