说明：  一个可以找到并发事件的算法。程序运用了闭包搜寻矩阵的算法。
(It is important in distributed computer systems to identify those events (at identifiable points in time) that are concurrent, or not related to each other in time. A group of concurrent events may sometimes attempt to simultaneously use the same resource, and this could cause problems. In this problem you will be supplied with lists of sequential events for an arbitrary number of computations, and the identification of an arbitrary number of messages sent between these computations. Let n be the number of events. Your task is to write an O(n3) program to find out how many pairs of events are concurrent)