
http://www.economics-ejournal.org/economics/journalarticles/2017-4

https://wiiw.ac.at/the-long-way-round-lessons-from-eu-cee-for-improving-integration-and-development-in-the-western-balkans-dlp-6194.pdf

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/