István Babcsányi A. Nagyr Mealy-Automata in Which the Output-Equivalence is a Congruence. 121-126 1994 11 Acta Cybern. 3 http://www.inf.u-szeged.hu/kutatas/actacybernetica/vol11n3/babcs/babcs.xml db/journals/actaC/actaC11.html#BabcsanyiN94