Andréka, Hajnal, S. Horváth, and István Németi. “Notes on Maximal Congruence Relations, Automata and Related Topics”. Acta Cybernetica 2, no. 1 (January 1, 1973): 71-88. Accessed November 26, 2024. https://cyber.bibl.u-szeged.hu/index.php/actcybern/article/view/3105.