Imreh, Balázs, Masami Ito, and A. Pukler. “On Commutative Asynchronous Nondeterministic Automata”. Acta Cybernetica 14, no. 4 (January 1, 2000): 607-617. Accessed April 26, 2024. https://cyber.bibl.u-szeged.hu/index.php/actcybern/article/view/3554.