Subdivisions of oriented cycles in digraphs with large chromatic number

2 COATI - Combinatorics, Optimization and Algorithms for Telecommunications
Laboratoire I3S - COMRED - COMmunications, Réseaux, systèmes Embarqués et Distribués, CRISAM - Inria Sophia Antipolis - Méditerranée
Abstract : An {\it oriented cycle} is an orientation of a undirected cycle. We first show that for any oriented cycle $C$, there are digraphs containing no subdivision of $C$ (as a subdigraph) and arbitrarily large chromatic number. In contrast, we show that for any $C$ is a cycle with two blocks, every strongly connected digraph with sufficiently large chromatic number contains a subdivision of $C$. We prove a similar result for the antidirected cycle on four vertices (in which two vertices have out-degree $2$ and two vertices have in-degree $2$).
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https://hal.inria.fr/hal-01277578
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Submitted on : Tuesday, February 23, 2016 - 3:42:13 PM
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• HAL Id : hal-01277578, version 1

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Nathann Cohen, Frédéric Havet, William Lochet, Nicolas Nisse. Subdivisions of oriented cycles in digraphs with large chromatic number. [Research Report] RR-8865, LRI - CNRS, University Paris-Sud; LIP - ENS Lyon; INRIA Sophia Antipolis - I3S. 2016, pp.25. ⟨hal-01277578⟩

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