+ /**
+ * @brief Computes the set of events that are not contained
+ * in the given configuration
+ *
+ * A configuration is a causally-closed, conflict-free set
+ * of events. Thus, you can determine which events lie outside
+ * of a configuration during the search more efficiently: the moment
+ * you discover an event contained in the configuration, you
+ * do not need to search that event or any of its ancestors as
+ * they will all be contained in the configuration
+ */