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Tutte, W. T., Graph Theory, Encyclopedia of Mathematics and its Applications 21, Reading, Massachusetts: Addison-Wesley: 15, 1984 [2022-11-06], ISBN 0-201-13520-5, MR 0746795, (原始内容存档于2022-01-07)
McColl, W. F.; Noshita, K., On the number of edges in the transitive closure of a graph, Discrete Applied Mathematics, 1986, 15 (1): 67–73, MR 0856101, doi:10.1016/0166-218X(86)90020-X
Joyner, David; Nguyen, Minh Van; Phillips, David, 1.6.1 Union, intersection, and join, Algorithmic Graph Theory and Sage 0.8-r1991, Google: 34–35, May 10, 2013 [2022-11-06], (原始内容存档于2016-01-16)
Tutte, W. T., Graph Theory, Encyclopedia of Mathematics and its Applications 21, Reading, Massachusetts: Addison-Wesley: 15, 1984 [2022-11-06], ISBN 0-201-13520-5, MR 0746795, (原始内容存档于2022-01-07)