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In the \textsc{Coloring Reconfiguration} problem, we are given two proper $k$-colorings of a graph and asked to decide whether one can be transformed into the other by repeatedly applying a specified recoloring rule, while maintaining a…

Data Structures and Algorithms · Computer Science 2025-11-11 Janosch Fuchs , Rin Saito , Tatsuhiro Suga , Takahiro Suzuki , Yuma Tamura

We consider Kempe changes on the $k$-colorings of a graph on $n$ vertices. If the graph is $(k-1)$-degenerate, then all its $k$-colorings are equivalent up to Kempe changes. However, the sequence between two $k$-colorings that arises from…

Combinatorics · Mathematics 2021-12-07 Marthe Bonamy , Vincent Delecroix , Clément Legrand-Duchesne

For graphs $G$ and $H$, a {\em homomorphism} from $G$ to $H$, or {\em $H$-coloring} of $G$, is an adjacency preserving map from the vertex set of $G$ to the vertex set of $H$. Writing ${\rm hom}(G,H)$ for the number of $H$-colorings…

Combinatorics · Mathematics 2012-06-15 David Galvin

Given a graph $G$, a decomposition of $G$ is a partition of its edges. A graph is $(d, h)$-decomposable if its edge set can be partitioned into a $d$-degenerate graph and a graph with maximum degree at most $h$. For $d \le 4$, we are…

Combinatorics · Mathematics 2020-07-06 Eun-Kyung Cho , Ilkyoo Choi , Ringi Kim , Boram Park , Tingting Shan , Xuding Zhu

A graph is 1-planar if it can be drawn on a plane so that each edge is crossed by at most one other edge. In this paper, we first give a useful structural theorem for 1-planar graphs, and then apply it to the list edge and list total…

Combinatorics · Mathematics 2019-12-17 Xin Zhang , Bei Niu , Jiguo Yu

Let $k$ be an integer. Two vertex $k$-colorings of a graph are \emph{adjacent} if they differ on exactly one vertex. A graph is \emph{$k$-mixing} if any proper $k$-coloring can be transformed into any other through a sequence of adjacent…

Discrete Mathematics · Computer Science 2013-02-15 Marthe Bonamy , Nicolas Bousquet

In this paper, we show that every $(2P_2,K_4)$-free graph is 4-colorable. The bound is attained by the five-wheel and the complement of the seven-cycle. This answers an open question by Wagon \cite{Wa80} in the 1980s. Our result can also be…

Combinatorics · Mathematics 2018-12-17 Serge Gaspers , Shenwei Huang

An $r$-edge coloring of a graph or hypergraph $G=(V,E)$ is a map $c:E\to \{0, \dots, r-1\}$. Extending results of Rado and answering questions of Rado, Gy\'arf\'as and S\'ark\"ozy we prove that (1.) the vertex set of every $r$-edge colored…

Combinatorics · Mathematics 2016-01-07 M. Elekes , D. T. Soukup , L. Soukup , Z. Szentmiklóssy

We introduce a new variant of graph coloring called correspondence coloring which generalizes list coloring and allows for reductions previously only possible for ordinary coloring. Using this tool, we prove that excluding cycles of lengths…

Combinatorics · Mathematics 2016-10-11 Zdenek Dvorak , Luke Postle

A proper edge coloring of a graph $G$ with colors $1,2,\dots,t$ is called a \emph{cyclic interval $t$-coloring} if for each vertex $v$ of $G$ the edges incident to $v$ are colored by consecutive colors, under the condition that color $1$ is…

Combinatorics · Mathematics 2017-03-30 Armen S. Asratian , Carl Johan Casselgren , Petros A. Petrosyan

A graph is $k$-planar if it can be drawn in the plane so that each edge is crossed at most $k$ times. Typically, the class of 1-planar graphs is among the most investigated graph families within the so-called "beyond planar graphs". A…

Combinatorics · Mathematics 2021-01-29 Xin Zhang , Yan Li

The equitable tree-coloring can formulate a structure decomposition problem on the communication network with some security considerations. Namely, an equitable tree-$k$-coloring of a graph is a vertex coloring using $k$ distinct colors…

Combinatorics · Mathematics 2021-04-13 Xin Zhang , Bei Niu , Yan Li , Bi Li

Defective coloring (also known as relaxed or improper coloring) is a generalization of proper coloring defined as follows: for $d \in \mathbb{N}$, a coloring of a graph is $d$-defective if every vertex is colored the same as at most $d$ of…

Combinatorics · Mathematics 2024-11-26 James Anderson

A star $k$-coloring is a proper $k$-coloring where the union of two color classes induces a star forest. While every planar graph is 4-colorable, not every planar graph is star 4-colorable. One method to produce a star 4-coloring is to…

Combinatorics · Mathematics 2015-10-13 Axel Brandt , Michael Ferrara , Mohit Kumbhat , Sarah Loeb , Derrick Stolee , Matthew Yancey

In a proper edge-coloring the edges of every color form a matching. A matching is induced if the end-vertices of its edges induce a matching. A strong edge-coloring is an edge-coloring in which the edges of every color form an induced…

Discrete Mathematics · Computer Science 2022-07-12 Hervé Hocquard , Dimitri Lajou , Borut Lu{ž}ar

A strong edge-coloring of a graph $G$ is an edge-coloring in which every color class is an induced matching, and the strong chromatic index $\chi_s'(G)$ is the minimum number of colors needed in strong edge-colorings of $G$. A graph is…

Combinatorics · Mathematics 2023-01-31 Gexin Yu , Rachel Yu

A strong edge-coloring of a graph $G$ is a coloring of edges of $G$ such that every color class forms an induced matching. The strong chromatic index is the minimum number of colors needed to color the graph. The Ore-degree $\theta(G)$ of a…

Combinatorics · Mathematics 2025-09-09 Seth Nelson , Gexin Yu

Graph coloring is fundamental to distributed computing. We give the first sub-logarithmic distributed algorithm for coloring cluster graphs. These graphs are obtained from the underlying communication network by contracting nodes and edges,…

Distributed, Parallel, and Cluster Computing · Computer Science 2025-06-17 Maxime Flin , Magnus M. Halldorsson , Alexandre Nolin

Recently, Borodin, Kostochka, and Yancey (On $1$-improper $2$-coloring of sparse graphs. Discrete Mathematics, 313(22), 2013) showed that the vertices of each planar graph of girth at least $7$ can be $2$-colored so that each color class…

Combinatorics · Mathematics 2015-07-13 Maria Axenovich , Torsten Ueckerdt , Pascal Weiner

We show that, for every $k \ge 2$, every $k$-uniform hypergaph of degree $\Delta$ and girth at least $5$ is efficiently $(1+o(1) )(k-1) (\Delta / \ln \Delta )^{ 1/(k-1) } $-list colorable. As an application (and to the best of our…

Discrete Mathematics · Computer Science 2026-02-10 Fotis Iliopoulos