Siman, Michael. “Equality Through Differentiation: Opt-Outs and Enhanced Cooperation As Expressions of Sovereignty”. Unequal Equals? The Status of Member States in an Integrating European Union, edited by Teszt Author and Teszt2 Author, Studies of the Central European Professors’ Network, 2026, pp. 235–277, https://doi.org/10.54237/profnet.2026.dsuesmsieu_7.