论文标题

证明了Gyárfás-Sumner的指示类似物,以$ P_4 $的方向

Proving a directed analogue of the Gyárfás-Sumner conjecture for orientations of $P_4$

论文作者

Cook, Linda, Masařík, Tomáš, Pilipczuk, Marcin, Reinald, Amadeus, Souza, Uéverton S.

论文摘要

面向图的图是一个不包含长度二的定向周期的挖掘图。如果$ d $不包含$ h $作为诱导的子(DI)图,则(定向)图$ d $是$ h $ free。 Gyárfás-Sumner的猜想是一个简单图表上的广泛开放的猜想,该猜想指出,对于任何森林$ f $,都有一些功能$ f $,因此每个$ f $ f $ f $ f $ g $带有clique number $ω(g)$的每个$ f $ g $,最多有$ f(g)的$ f(g))$。 Aboulker,Charbit和Naserasr [Gyárfás-Sumner的延伸到Digraphs; E-JC 2021]提出了这种猜想对定向图的类似物。 Digraph $ d $的二分法数是为$ d $的顶点集染色所需的最低颜色数量,因此$ d $中没有定向周期是单色的。 Aboulker, Charbit, and Naserasr's $\overrightarrowχ$-boundedness conjecture states that for every oriented forest $F$, there is some function $f$ such that every $F$-free oriented graph $D$ has dichromatic number at most $f(ω(D))$, where $ω(D)$ is the size of a maximum clique in the graph underlying $D$.在本文中,我们朝着证明Aboulker,Charbit和Naserasr的$ \oferrightarrowχ$结合的猜想迈出的第一步,是通过证明$ f $是四个顶点的任何路径方向而保持的。

An oriented graph is a digraph that does not contain a directed cycle of length two. An (oriented) graph $D$ is $H$-free if $D$ does not contain $H$ as an induced sub(di)graph. The Gyárfás-Sumner conjecture is a widely-open conjecture on simple graphs, which states that for any forest $F$, there is some function $f$ such that every $F$-free graph $G$ with clique number $ω(G)$ has chromatic number at most $f(ω(G))$. Aboulker, Charbit, and Naserasr [Extension of Gyárfás-Sumner Conjecture to Digraphs; E-JC 2021] proposed an analogue of this conjecture to the dichromatic number of oriented graphs. The dichromatic number of a digraph $D$ is the minimum number of colors required to color the vertex set of $D$ so that no directed cycle in $D$ is monochromatic. Aboulker, Charbit, and Naserasr's $\overrightarrowχ$-boundedness conjecture states that for every oriented forest $F$, there is some function $f$ such that every $F$-free oriented graph $D$ has dichromatic number at most $f(ω(D))$, where $ω(D)$ is the size of a maximum clique in the graph underlying $D$. In this paper, we perform the first step towards proving Aboulker, Charbit, and Naserasr's $\overrightarrowχ$-boundedness conjecture by showing that it holds when $F$ is any orientation of a path on four vertices.

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