Abstract
Let H be the digraph with vertex set \(\{1,2,3,4\}\) and arc set \(\{12,13,14,24,34\}\). In this paper, we determine the maximum size of H-free digraphs of order n as well as the extremal digraphs attaining this maximum size when \(n\ge 16\).
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Acknowledgements
The author thanks Professor Zejun Huang for his helpful suggestions. Part of this work was done when Lyu was visiting Auburn University with the financial support of China Scholarship Council. He would like to acknowledge Professor Tin-Yau Tam for his support and hospitality.
Funding
Zhenhua Lyu was supported by the Start-up Grant for New Faculty of Shenyang Aerospace University (19YB53).
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Lyu, Z. Extremal Digraphs Avoiding an Orientation of the Diamond. Graphs and Combinatorics 37, 1373–1383 (2021). https://doi.org/10.1007/s00373-021-02324-7
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DOI: https://doi.org/10.1007/s00373-021-02324-7