Ésik, Zoltán, and Balázs Imreh. “Subdirectly Irreducible Commutative Automata”. Acta Cybernetica 5, no. 3 (January 1, 1981): 251-260. Accessed April 25, 2024. https://cyber.bibl.u-szeged.hu/index.php/actcybern/article/view/3217.