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A proper coloring of a graph is called \emph{odd} if every non-isolated vertex has some color that appears an odd number of times on its neighborhood. The smallest number of colors that admits an odd coloring of a graph $G$ is denoted…

Combinatorics · Mathematics 2024-12-06 Daniel W. Cranston

We study vertex colorings of the square $G^2$ of an outerplanar graph $G$. We find the optimal bound of the inductiveness, chromatic number and the clique number of $G^2$ as a function of the maximum degree $\Delta$ of $G$ for all…

Combinatorics · Mathematics 2007-06-12 Geir Agnarsson , Magnus Mar Halldorsson

A strong edge-coloring of a graph $G$ is a coloring of the edges such that every color class induces a matching in $G$. The strong chromatic index of a graph is the minimum number of colors needed in a strong edge-coloring of the graph. In…

Combinatorics · Mathematics 2018-06-20 Mingfang Huang , Michael Santana , Gexin Yu

We prove that graphs excluding a fixed immersion have bounded nonrepetitive chromatic number. More generally, we prove that if $H$ is a fixed planar graph that has a planar embedding with all the vertices with degree at least 4 on a single…

Combinatorics · Mathematics 2019-07-15 Paul Wollan , David R. Wood

A strong edge coloring of a graph $G$ is a proper edge coloring of $G$ such that every color class is an induced matching. The minimum number of colors required is termed the strong chromatic index. In this paper, we determine the exact…

Combinatorics · Mathematics 2021-07-12 Suresh Dara , Suchismita Mishra , Narayanan Narayanan , Zsolt Tuza

The proper conflict-free chromatic number, $\chi_{pcf}(G)$, of a graph $G$ is the least $k$ such that $G$ has a proper $k$-coloring in which for each non-isolated vertex there is a color appearing exactly once among its neighbors. The…

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 $G \in \mathcal{G}^*$…

Combinatorics · Mathematics 2017-11-21 Jessica McDonald , Gregory J. Puleo

We call an oriented odd cycle alternating if it has exactly one vertex whose in-degree and out-degree are both positive. In this paper, we investigate whether certain graphs admit an orientation that avoids alternating odd cycles as…

Combinatorics · Mathematics 2025-08-27 Nóra Almási , Gábor Simonyi

Odd coloring is a proper coloring with an additional restriction that every non-isolated vertex has some color that appears an odd number of times in its neighborhood. The minimum number of colors $k$ that can ensure an odd coloring of a…

Combinatorics · Mathematics 2022-06-16 Fangyu Tian , Yuxue Yin

We prove for k at most 10, that every graph of chromatic number k with a unique k-coloring admits a clique minor of order k.

Combinatorics · Mathematics 2020-02-20 Matthias Kriesell

The strong chromatic index of a multigraph is the minimum $k$ such that the edge set can be $k$-colored requiring that each color class induces a matching. We verify a conjecture of Faudree, Gy\'{a}rf\'{a}s, Schelp and Tuza, showing that…

Combinatorics · Mathematics 2015-08-03 A. V. Kostochka , X. Li , W. Ruksasakchai , M. Santana , T. Wang , G. Yu

The proper chromatic number $\Vec{\chi}(G)$ of a graph $G$ is the minimum $k$ such that there exists an orientation of the edges of $G$ with all vertex-outdegrees at most $k$ and such that for any adjacent vertices, the outdegrees are…

Combinatorics · Mathematics 2022-12-09 Yaobin Chen , Bojan Mohar , Hehui Wu

Weak and strong coloring numbers are generalizations of the degeneracy of a graph, where for each natural number $k$, we seek a vertex ordering such every vertex can (weakly respectively strongly) reach in $k$ steps only few vertices with…

Combinatorics · Mathematics 2021-04-08 Zdeněk Dvořák , Jakub Pekárek , Torsten Ueckerdt , Yelena Yuditsky

A strong edge-coloring of a graph $G$ is an edge-coloring such that no two edges of distance at most two receive the same color. The strong chromatic index $\chi'_s(G)$ is the minimum number of colors in a strong edge-coloring of $G$. P.…

Combinatorics · Mathematics 2015-10-06 Chuanyun Zang

In this short note, we extend the result of Galluccio, Goddyn, and Hell, which states that graphs of large girth excluding a minor are nearly bipartite. We also prove a similar result for the oriented chromatic number, from which follows in…

Combinatorics · Mathematics 2014-02-14 Jaroslav Nesetril , Patrice Ossona De Mendez

A b-coloring of a graph is a proper coloring of its vertices such that each color class contains a vertex adjacent to at least one vertex of every other color class. The b-chromatic number of a graph is the largest integer k such that the…

Combinatorics · Mathematics 2019-04-04 Renata Del-Vecchio , Mekkia Kouider

In this paper, we introduce the notion of 2-boundary planar graphs. A graph is 2-boundary planar if it has an embedding in the plane so that all vertices lie on the boundary of at most two faces and no edges are crossed. A proper coloring…

Combinatorics · Mathematics 2025-04-07 Weichan Liu , Mengke Qi , Xin Zhang

Motivated by Hadwiger's conjecture and related problems for list-coloring, we study graphs $H$ for which every graph with minimum degree at least $|V(H)|-1$ contains $H$ as a minor. We prove that a large class of apex-outerplanar graphs…

Combinatorics · Mathematics 2024-03-19 Chun-Hung Liu , Youngho Yoo

Given a graph $G$ and a nondecreasing sequence $S=(s_1,\ldots,s_k)$ of positive integers, the mapping $c:V(G)\longrightarrow \{1,\ldots,k\}$ is called an $S$-packing coloring of $G$ if for any two distinct vertices $x$ and $y$ in…

Combinatorics · Mathematics 2020-04-14 Boštjan Brešar , Nicolas Gastineau , Olivier Togni

In this paper, we study the achromatic and the pseudoachromatic numbers of planar and outerplanar graphs as well as planar graphs of girth 4 and graphs embedded on a surface. We give asymptotically tight results and lower bounds for maximal…