Demetrovics, János. “On the Interaction Between Closure Operations and Choice Functions With Applications to Relational Databases”. Acta Cybernetica 10, no. 3 (January 1, 1992): 129-139. Accessed April 27, 2024. https://cyber.bibl.u-szeged.hu/index.php/actcybern/article/view/3401.