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arXiv · 2009.07239

Generalizations and strengthenings of Ryser's conjecture

Louis DeBiasio·Yigal Kamel·Grace McCourt·Hannah Sheats
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Abstract

Ryser's conjecture says that for every $r$-partite hypergraph $H$ with matching number $\nu(H)$, the vertex cover number is at most $(r-1)\nu(H)$. This far reaching generalization of K\"onig's theorem is only known to be true for $r\leq 3$, or $\nu(G)=1$ and $r\leq 5$. An equivalent formulation of Ryser's conjecture is that in every $r$-edge coloring of a graph $G$ with independence number $\alpha(G)$, there exists at most $(r-1)\alpha(G)$ monochromatic connected subgraphs which cover the vertex set of $G$. We make the case that this latter formulation of Ryser's conjecture naturally leads to a variety of stronger conjectures and generalizations to hypergraphs and multipartite graphs. Regarding these generalizations and strengthenings, we survey the known results, improving upon some, and we introduce a collection of new problems and results.

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Louis DeBiasio, Yigal Kamel, Grace McCourt, Hannah Sheats. 2020-09-15. Generalizations and strengthenings of Ryser's conjecture. https://arxiv.org/abs/2009.07239

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