It is known that event-clock automata of Alur, Fix and Henzinger are a decidable subclass of timed automata. However the proof in that paper is given only for the automata without epsilon-transitions. We study here the problem of removing epsilon transitions from event-clock automata such that the Alur, Fix and Henzinger's construction can be applied. The idea is to shift the constraint to be checked on each epsilon transition to the closest non-epsilon transition. We define also a notion of hierarchic cooperation that allows the epsilon transitions to be removed all at a time, thus avoiding the problem of finding a well-founded ordering, problem that appears if we try to remove these transitions iteratively.
Published in the Proceedings of CITTI 2000.