Volume 96, Issue 2 pp. 289-309
ARTICLE

Zip product of graphs and crossing numbers

Zhangdong Ouyang

Corresponding Author

Zhangdong Ouyang

Department of Mathematics, Hunan First Normal University, Changsha, China

Correspondence Zhangdong Ouyang, Department of Mathematics, Hunan First Normal University, 410205 Changsha, China.

Email: [email protected]

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Yuanqiu Huang

Yuanqiu Huang

Department of Mathematics, Hunan Normal University, Changsha, China

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Fengming Dong

Fengming Dong

Mathematics and Mathematics Education, National Institute of Education, Nanyang Technological University, Singapore, Singapore

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Eng Guan Tay

Eng Guan Tay

Mathematics and Mathematics Education, National Institute of Education, Nanyang Technological University, Singapore, Singapore

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First published: 14 July 2020
Citations: 2

Abstract

D. Bokal proved that the crossing number is additive for the zip product under the condition of having two coherent bundles in the zipped graphs. This property is very effective when dealing with the crossing numbers of (capped) Cartesian product of trees with graphs containing a dominating vertex. In this paper, we first prove that the crossing number is still additive for the zip product under a weaker condition. Based on the new condition, we then establish some general expressions for bounding the crossing numbers of (capped) Cartesian product of trees with graphs (possibly without dominating vertex). Exact values of the crossing numbers of Cartesian product of trees with most graphs of order at most five are obtained by applying these expressions, which extend some previous results due to M. Klešč. In fact, our results can also be applied to deal with Cartesian product of trees with graphs of order more than five.

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