Abstract : A famous conjecture of Gyárfás and Sumner states for any tree T and integer k, if the chromatic number of a graph is large enough, either the graph contains a clique of size k or it contains T as an induced subgraph. We discuss some results and open problems about extensions of this conjecture to oriented graphs. We conjecture that for every oriented star S and integer k, if the chromatic number of a digraph is large enough, either the digraph contains a clique of size k or it contains S as an induced subgraph. As an evidence, we prove that for any oriented star S, every oriented graph with sufficiently large chromatic number contains either a transitive tournament of order 3 or S as an induced subdigraph. We then study for which sets P of orientations of P 4 (the path on four vertices) similar statements hold. We establish some positive and negative results.
https://hal.inria.fr/hal-01882395
Contributeur : Frederic Havet
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Soumis le : vendredi 21 décembre 2018 - 08:59:49
Dernière modification le : vendredi 4 janvier 2019 - 17:33:38
P. Aboulker, J. Bang-Jensen, Nicolas Bousquet, Pierre Charbit, Frédéric Havet, et al.. $χ$-bounded families of oriented graphs. Journal of Graph Theory, Wiley, 2018, 89 (3), pp.304 - 326. 〈10.1002/jgt.22252〉. 〈hal-01882395〉
