For an acyclic network, it is possible to number the nodes so that if arc (i,j) exists, then i < j. Acyclic networks do not have "loops" (cycles). A loop or cycle is a path that returns to a node previously left. Following picture is an acyclic network. If the arcs correspond to activities that have a time sequence, the network is naturally acyclic. For example, project management networks are acyclic.