1. Graphs and Digraphs;Behzad,1979
2. Coverings of bipartite graphs;Dulmage;Canad. J. Math.,1958
3. On the core of a graph;Harary,1967
4. Girth and independence ratio;Hopkins;Canad. Math. Bull.,1982
5. J. A. Suškov, (1. q)-matchings, Vestnik Leningrad. Univ. 1975 no. 19, Mat. Meh. Astronom. vyp. 4, 50–55.