Fong, Yuen, Feng-Kuo Huang, and Richard Wiegandt. “Radical Theory for Group Semiautomata”. Acta Cybernetica 11, no. 3 (January 1, 1994): 169-188. Accessed May 3, 2024. https://cyber.bibl.u-szeged.hu/index.php/actcybern/article/view/3427.