A contradictory phenomenon between two events in Petri net. It means that several events share a precondition or share a postcondition. In this situation, only one of these events mayoccur. petri网中两个事件间的矛盾现象,指的是多个事件共享一个事前条件或共享一个事后条件。在此情况下这些事件中只有一个可能发生。