https://www.consilium.europa.eu/en/meetings/international-summit/2021/10/06/
http://www.elperiodico.com/es/politica/20171226/que-es-tabarnia-propuesta-secesion-barcelona-tarragona-resto-cataluna-6517873
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/