A subset of the vertex set of a graph is a feedback vertex set of the graph if the resulting graph is acyclic after removing the vertex subset from the graph.
若从一个图中去掉某些顶点后得到的导出子图是无圈图，则所去的那些顶点组成的集合就是原图的反馈点集。
2
The set of jobs is specified using a directed acyclic graph, where each job is a node in the graph. Jobs are submitted to Condor following the dependencies given by the graph.