About subdivisions of four blocks cycles $C(k_1,1,k_3,1)$ in digraphs with large chromatic number
| Autor: | Al-Mniny, Darine, Zayat, Soukaina |
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| Rok vydání: | 2023 |
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| Druh dokumentu: | Working Paper |
| Popis: | A cycle with four blocks $C(k_{1}, k_{2},k_{3},k_{4})$ is an oriented cycle formed of four blocks of lengths $k_{1}, k_{2}, k_{3}$ and $k_{4}$ respectively. Recently, Cohen et al. conjectured that for every positive integers $k_{1}, k_{2}, k_{3}, k_{4}$, there is an integer $g(k_{1},k_{2},k_{3},k_{4})$ such that every strongly connected digraph $D$ containing no subdivisions of $C(k_{1},k_{2},k_{3},k_{4})$ has a chromatic number at most $g(k_{1},k_{2},k_{3},k_{4})$. This conjecture is confirmed by Cohen et al. for the case of $C(1,1,1,1)$ and by Al-Mniny for the case of $C(k_1,1,1,1)$. In this paper, we affirm Cohen et al.'s conjecture for the case where $k_2=k_4=1$, namely $g(k_1,1,k_3,1) =O({(k_1+k_3)}^2)$. Moreover, we show that if in addition $D$ is Hamiltonian, then the chromatic number of $D$ is at most $6k$, with $k=\textrm{max}\{k_1,k_3\}.$ Comment: 23 pages |
| Databáze: | arXiv |
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