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We study the class of simple graphs $\mathcal{G}^*$ for which every pair of distinct odd cycles intersect in at most one edge. We give a structural characterization of the graphs in $\mathcal{G}^*$ and prove that every $G \in \mathcal{G}^*$…

组合数学 · 数学 2017-11-21 Jessica McDonald , Gregory J. Puleo

An acyclic edge coloring of a graph $G$ is a proper edge coloring such that no bichromatic cycles are produced. The acyclic edge coloring conjecture by Fiam{\v{c}}ik (1978) and Alon, Sudakov and Zaks (2001) states that every simple graph…

离散数学 · 计算机科学 2020-05-14 Qiaojun Shu , Guohui Lin , Eiji Miyano

It is well-known that an undirected graph has no odd cycle if and only if it is bipartite. A less obvious, but similar result holds for directed graphs: a strongly connected digraph has no odd cycle if and only if it is bipartite. Can this…

组合数学 · 数学 2016-05-02 Gregory Gutin , Bin Sheng , Magnus Wahlström

It was conjectured by the third author in about 1973 that every $d$-regular planar graph (possibly with parallel edges) can be $d$-edge-coloured, provided that for every odd set $X$ of vertices, there are at least $d$ edges between $X$ and…

离散数学 · 计算机科学 2012-09-07 Maria Chudnovsky , Katherine Edwards , Paul Seymour

A conjecture due to the fourth author states that every $d$-regular planar multigraph can be $d$-edge-coloured, provided that for every odd set $X$ of vertices, there are at least $d$ edges between $X$ and its complement. For $d = 3$ this…

离散数学 · 计算机科学 2012-10-30 Maria Chudnovsky , Katherine Edwards , Ken-ichi Kawarabayashi , Paul Seymour

Fix a palette $\mathcal K$ of $\Delta+1$ colours, a graph with maximum degree $\Delta$, and a subset $M$ of the edge set with minimum distance between edges at least $9$. If the edges of $M$ are arbitrarily precoloured from $\mathcal K$,…

组合数学 · 数学 2018-12-31 António Girão , Ross J. Kang

Edwards, van den Heuvel, Kang, and Sereni conjectured the following strengthening of Vizing's Theorem: let $G$ be a simple graph, and let $K = \Delta(G) + 1$. For any matching $M$ in $G$ and any precoloring of the edges in $M$ using the…

组合数学 · 数学 2016-08-18 Gregory J. Puleo

A properly colored cycle (path) in an edge-colored graph is a cycle (path) with consecutive edges assigned distinct colors. A monochromatic triangle is a cycle of length $3$ with the edges assigned a same color. It is known that every…

组合数学 · 数学 2020-08-24 Ruonan Li

In an edge-colored graph $(G,c)$, let $d^c(v)$ denote the number of colors on the edges incident with a vertex $v$ of $G$ and $\delta^c(G)$ denote the minimum value of $d^c(v)$ over all vertices $v\in V(G)$. A cycle of $(G,c)$ is called…

组合数学 · 数学 2020-07-29 Xiaozheng Chen , Xueliang Li

Let $G = (V, E)$ be an $n$-vertex edge-colored graph. In 2013, H. Li proved that if every vertex $v \in V$ is incident to at least $(n+1)/2$ distinctly colored edges, then $G$ admits a rainbow triangle. We prove that the same hypothesis…

组合数学 · 数学 2021-02-24 Andrzej Czygrinow , Theodore Molla , Brendan Nagle , Roy Oursler

Grotzsch proved that every triangle-free planar graph is 3-colorable. Thomassen proved that every planar graph of girth at least five is 3-choosable. As for other surfaces, Thomassen proved that there are only finitely many 4-critical…

组合数学 · 数学 2017-10-20 Luke Postle

The classical theorem of Vizing states that every graph of maximum degree $d$ admits an edge-coloring with at most $d+1$ colors. Furthermore, as it was earlier shown by K\H{o}nig, $d$ colors suffice if the graph is bipartite. We investigate…

组合数学 · 数学 2016-08-23 Endre Csóka , Gabor Lippner , Oleg Pikhurko

An odd $k$-edge-coloring of a graph $G$ is a (not necessarily proper) edge-coloring with at most $k$ colors such that each non-empty color class induces a graph in which every vertex is of odd degree; similarly, if more than one color per…

组合数学 · 数学 2025-06-26 Xiao-Chuan Liu , Mirko Petruševski , Xu Yang

The notion of a Galvin orientation of a line graph is introduced, generalizing the idea used by Galvin in his landmark proof of the list-edge-colouring conjecture for bipartite graphs. If L(G) has a proper Galvin orientation with respect to…

组合数学 · 数学 2015-08-11 Jessica McDonald

In this paper, we aim to introduce the group version of edge coloring and list edge coloring, and prove that all 2-degenerate graphs along with some planar graphs without adjacent short cycles is group $(\Delta(G)+1)$-edge-choosable while…

组合数学 · 数学 2011-05-31 Xin Zhang , Guizhen Liu

A graph is apex if there is a vertex whose deletion makes the graph planar, and doublecross if it can be drawn in the plane with only two crossings, both incident with the infinite region in the natural sense. In 1966, Tutte conjectured…

组合数学 · 数学 2017-03-28 Katherine Edwards , Daniel P. Sanders , Paul Seymour , Robin Thomas

An edge coloring of a graph $G$ is to color all the edges in the graph such that adjacent edges receive different colors. It is acyclic if each cycle in the graph receives at least three colors. Fiam{\v{c}}ik (1978) and Alon, Sudakov and…

离散数学 · 计算机科学 2023-06-29 Qiaojun Shu , Guohui Lin

We prove that for a line perfect multigraph the chromatic index is equal to the list chromatic index. This is a generalization of Galvin's result on bipartite multigraphs. Soon after the first version was submitted to arxiv, I found out…

组合数学 · 数学 2019-09-09 Alexey Gordeev

We first give an alternative proof of the Alon-Tarsi list coloring theorem. We use the ideas from this proof to obtain the following result, which is an additive coloring analog of the Alon-Tarsi Theorem: Let $G$ be a graph and let $D$ be…

组合数学 · 数学 2024-07-15 Ian Gossett

In this paper we have shown without assuming the four color theorem of planar graphs that every (bridgeless) cubic planar graph has a three-edge-coloring. This is an old-conjecture due to Tait in the squeal of efforts in settling the…

组合数学 · 数学 2007-05-23 I. Cahit
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