Abstract
In 1985, Mader conjectured that for every acyclic digraph F there exists K = K(F) such that every digraph D with minimum out-degree at least K contains a subdivision of F. This conjecture remains widely open, even for digraphs F on five vertices. Recently, Aboulker, Cohen, Havet, Lochet, Moura and Thomassé studied special cases of Mader’s problem and made the following conjecture: for every ℓ ≥ 2 there exists K = K(ℓ) such that every digraph D with minimum out-degree at least K contains a subdivision of every orientation of a cycle of length ℓ.
We prove this conjecture and answer further open questions raised by Aboulker et al.
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Acknowledgement
The research on this project was initiated during a joint research workshop of Tel Aviv University and the Freie Universität Berlin on Ramsey Theory, held in Tel Aviv in March 2020, and partially supported by GIF grant G-1347-304.6/2016. We would like to thank the German-Israeli Foundation (GIF) and both institutions for their support.
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During the work on this project, the author was supported by ERC Starting Grant 633509.
Funded by DFG-GRK 2434 Facets of Complexity.
Research supported in part by GIF grant No. G-1347-304.6/2016 and by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy - The Berlin Mathematics Research Center MATH+ (EXC-2046/1, project ID: 390685689).
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Gishboliner, L., Steiner, R. & Szabó, T. Oriented Cycles in Digraphs of Large Outdegree. Combinatorica 42 (Suppl 1), 1145–1187 (2022). https://doi.org/10.1007/s00493-021-4750-z
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DOI: https://doi.org/10.1007/s00493-021-4750-z
Mathematics Subject Classification (2010)
- 05C07
- 05C20
- 05C83