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A graph G is (a:b)-colorable if there exists an assignment of b-element subsets of {1,...,a} to vertices of G such that sets assigned to adjacent vertices are disjoint. We show that every planar graph without cycles of length 4 or 5 is…

Combinatorics · Mathematics 2019-07-16 Zdeněk Dvořák , Xiaolan Hu

A digraph is semicomplete multipartite if its underlying graph is a complete multipartite graph. As a special case of semicomplete multipartite digraphs, J{\o}rgensen et al. \cite{JG14} initiated the study of doubly regular team…

Combinatorics · Mathematics 2025-01-22 Shuang Li , Yuefeng Yang , Kaishun Wang

The spectral excess theorem for distance-regular graphs states that a regular (connected) graph is distance-regular if and only if its spectral-excess equals its average excess. A bipartite graph is distance-biregular when it is…

Combinatorics · Mathematics 2013-04-17 M. A. Fiol

A circuit double cover of a bridgeless graph is a collection of even subgraphs such that every edge is contained in exactly two subgraphs of the given collection. Such a circuit double cover describes an embedding of the corresponding graph…

Combinatorics · Mathematics 2026-01-16 Meike Weiß , Reymond Akpanya , Alice C. Niemeyer

A graph is \emph{$(\mathcal{I}, \mathcal{F})$-partitionable} if its vertex set can be partitioned into two parts such that one part $\mathcal{I}$ is an independent set, and the other $\mathcal{F}$ induces a forest. A graph is…

Combinatorics · Mathematics 2025-02-27 Zhengjiao Liu , Tao Wang , Xiaojing Yang

Motivated by problems modeling the spread of infections in networks, in this paper we explore which bipartite graphs are most resilient to widespread infections under various parameter settings. Namely, we study bipartite networks with a…

Data Structures and Algorithms · Computer Science 2018-01-10 Shelby Heinecke , Will Perkins , Lev Reyzin

We present an algorithm for determining whether a bipartite graph $G$ is 2-chordal (formerly doubly chordal bipartite). At its core this algorithm is an extension of the existing efficient algorithm for determining whether a graph is…

Combinatorics · Mathematics 2021-04-13 Austin Alderete

We show that every cubic graph on $n$ vertices contains a spanning subgraph in which the number of vertices of each degree deviates from $\frac{n}{4}$ by at most $\frac{1}{2}$, up to three exceptions. This resolves the conjecture of Alon…

Combinatorics · Mathematics 2025-05-13 Borut Lužar , Jakub Przybyło , Roman Soták

A graph $G = (V, E)$ is \emph{partitionable} if there exists a partition $\{A, B\}$ of $V$ such that $A$ induces a disjoint union of cliques and $B$ induces a triangle-free graph. In this paper we investigate the computational complexity of…

Computational Complexity · Computer Science 2015-01-06 Faisal N. Abu-Khzam , Carl Feghali , Haiko Müller

We completely characterize triangulations of the projective plane that have a spanning bipartite quadrangulation subgraph. This is an affirmative answer to a question by K\"undgen and Ramamurthi (J Combin Theory Ser B 85, 307--337, 2002)…

Combinatorics · Mathematics 2026-04-24 Kenta Noguchi

A simple undirected graph is said to be {\em semisymmetric} if it is regular and edge-transitive but not vertex-transitive. Every semisymmetric graph is a bipartite graph with two parts of equal size. It was proved in [{\em J. Combin.…

Combinatorics · Mathematics 2012-06-12 Li Wang , Shaofei Du

We provide precise asymptotic estimates for the number of several classes of labelled cubic planar graphs, and we analyze properties of such random graphs under the uniform distribution. This model was first analyzed by Bodirsky et al.…

Combinatorics · Mathematics 2019-07-26 Marc Noy , Clément Requilé , Juanjo Rué

We study biplane graphs drawn on a finite point set $S$ in the plane in general position. This is the family of geometric graphs whose vertex set is $S$ and which can be decomposed into two plane graphs. We show that every sufficiently…

Computational Geometry · Computer Science 2017-08-10 Alfredo García , Ferran Hurtado , Matias Korman , Inês Matos , Maria Saumell , Rodrigo I. Silveira , Javier Tejel , Csaba D. Tóth

A half-square of a bipartite graph $B=(X,Y,E_B)$ has one color class of $B$ as vertex set, say $X$; two vertices are adjacent whenever they have a common neighbor in $Y$. If $G=(V,E_G)$ is the half-square of a planar bipartite graph…

Discrete Mathematics · Computer Science 2018-12-12 Hoang-Oanh Le , Van Bang Le

Given a family $\mathcal{F}$ of bipartite graphs, the {\it Zarankiewicz number} $z(m,n,\mathcal{F})$ is the maximum number of edges in an $m$ by $n$ bipartite graph $G$ that does not contain any member of $\mathcal{F}$ as a subgraph (such…

Combinatorics · Mathematics 2023-01-11 Tao Jiang , Sean Longbrake , Jie Ma

Let $R$ and $B$ be two disjoint sets of points in the plane such that $|B|\leqslant |R|$, and no three points of $R\cup B$ are collinear. We show that the geometric complete bipartite graph $K(R,B)$ contains a non-crossing spanning tree…

Computational Geometry · Computer Science 2015-12-10 Ahmad Biniaz , Prosenjit Bose , Anil Maheshwari , Michiel Smid

A $k$-stack (respectively, $k$-queue) layout of a graph consists of a total order of the vertices, and a partition of the edges into $k$ sets of non-crossing (non-nested) edges with respect to the vertex ordering. In 1992, Heath and…

Computational Geometry · Computer Science 2018-01-17 Sergey Pupyrev

We derive a quadratic-time algorithm for the genus distribution of any 3-regular, biconnected series-parallel graph, which we extend to any biconnected series-parallel graph of maximum degree at most 3. Since the biconnected components of…

Discrete Mathematics · Computer Science 2014-07-31 Jonathan L. Gross , Michal Kotrbčík , Timothy Sun

The Unfriendly Partition Problem asks whether it is possible to split the vertex set of an infinite graph $G$ into two parts so that every vertex has at least as many neighbors in the other part than on its own. Despite the uncountable…

Combinatorics · Mathematics 2024-12-19 Leandro Fiorini Aurichi , Lucas Real

Bipartite graphs model the relationship between two disjoint sets of objects. They have a wide range of applications and are often visualized as a 2-layered drawing, where each set of objects is visualized as a set of vertices (points) on…

Computational Geometry · Computer Science 2022-08-30 Reyan Ahmed , Stephen Kobourov , Myroslav Kryven