Kubin T. Enhanced cooperation in the European Union for the third time. The progressing diversity of integration, and the development of enhanced cooperation and its importance for the functioning of the EU. 10.14746/rie [Internet]. 2015 Jun. 15 [cited 2024 Jul. 17];(9):57-75. Available from: https://pressto.amu.edu.pl/index.php/rie/article/view/6188