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Let $G$ be a bridgeless cubic graph. The Berge--Fulkerson Conjecture (1970s) states that $G$ admits a list of six perfect matchings such that each edge of $G$ belongs to exactly two of these perfect matchings. If answered in the…

Combinatorics · Mathematics 2023-01-02 František Kardoš , Edita Máčajová , Jean Paul Zerafa

For a simple graph $G=(V,E)$ without any isolated vertex, a cosecure dominating set $D$ of $G$ satisfies the following two properties (i) $S$ is a dominating set of $G$, (ii) for every vertex $v \in S$ there exists a vertex $u \in V…

Discrete Mathematics · Computer Science 2023-02-28 Kusum , Arti Pandey

A connected graph $G$ with at least two vertices is matching covered if each of its edges lies in a perfect matching. A matching covered graph is minimal if the removal of any edge results in a graph that is no longer matching covered. An…

Combinatorics · Mathematics 2026-04-02 Xiaoling He , Fuliang Lu , Heping Zhang

Let ind-match$(G)$, min-match$(G)$ and match$(G)$ denote the induced matching number, minimum matching number and matching number of a graph $G$, respectively. It is known that ind-match$(G) \leq $ min-match$(G) \leq {\rm match}(G) \leq$…

Combinatorics · Mathematics 2025-03-10 Kazunori Matsuda , Ryosuke Sato , Yuichi Yoshida

A connected nontrivial graph $G$ is {\it matching covered} if every edge of $G$ is contained in some perfect matching of $G$. A matching covered graph $G$ is {\it minimal} if $G-e$ is not matching covered for each edge $e$ of $G$. A graph…

Combinatorics · Mathematics 2025-12-01 Liwen Lian , Jinfeng Liu , Mengyuan Niu , Xiumei Wang

The toughness of a graph $G$ is defined as the largest real number $t$ such that for any set $S\subseteq V(G)$ such that $G-S$ is disconnected, $S$ has at least $t$ times more elements than $G-S$ has components (unless $G$ is complete, in…

Combinatorics · Mathematics 2026-03-06 J. Pascal Gollin , Martin Milanič , Laura Ogrin

A path in an edge-colored graph is called a proper path if no two adjacent edges of the path are colored with one same color. An edge-colored graph is called $k$-proper connected if any two vertices of the graph are connected by $k$…

Combinatorics · Mathematics 2015-07-13 Fei Huang , Xueliang Li , Shujing Wang

The anti-forcing number of a perfect matching $M$ of a graph $G$ is the minimal number of edges not in $M$ whose removal to make $M$ as a unique perfect matching of the resulting graph. The set of anti-forcing numbers of all perfect…

Combinatorics · Mathematics 2016-07-20 Kai Deng , Heping Zhang

Since a plurality of processors in a distributed computer system working in parallel, to ensure the fault tolerance and stability of the network is an important issue in distributed systems. As the topology of the distributed network can be…

Combinatorics · Mathematics 2020-12-17 Xin Wang , Chaoqun Ma , Jia Guo

For a graph $G$ define the parameters $\ell(G)$ and $L(G)$ as the minimum and maximum value of $\nu(G\backslash F)$, where $F$ is a maximum matching of $G$ and $\nu(G)$ is the matching number of $G$. In this paper, we show that there is a…

Combinatorics · Mathematics 2025-04-29 Vahan Mkrtchyan

In the spanning tree congestion problem, given a connected graph $G$, the objective is to compute a spanning tree $T$ in $G$ that minimizes its maximum edge congestion, where the congestion of an edge $e$ of $T$ is the number of edges in…

Computational Complexity · Computer Science 2023-07-12 Huong Luu , Marek Chrobak

The competition graph of a digraph $D$ is a (simple undirected) graph which has the same vertex set as $D$ and has an edge between two distinct vertices $x$ and $y$ if and only if there exists a vertex $v$ in $D$ such that $(x,v)$ and…

Combinatorics · Mathematics 2013-12-25 Suh-Ryung Kim , Jung Yeun Lee , Boram Park , Yoshio Sano

Given a graph $G$, the zero forcing number of $G$, $Z(G)$, is the smallest cardinality of any set $S$ of vertices on which repeated applications of the forcing rule results in all vertices being in $S$. The forcing rule is: if a vertex $v$…

Combinatorics · Mathematics 2022-09-21 Aidan Johnson , Andrew E. Vick , Darren A. Narayan

The edge domination number $\gamma_e(G)$ of a graph $G$ is the minimum size of a maximal matching in $G$. It is well known that this parameter is computationally very hard, and several approximation algorithms and heuristics have been…

Combinatorics · Mathematics 2019-05-30 Julien Baste , Maximilian Fürst , Michael A. Henning , Elena Mohr , Dieter Rautenbach

A matching covered graph $G$ is minimal if for each edge $e$ of $G$, $G-e$ is not matching covered. An edge $e$ of a matching covered graph $G$ is removable if $G-e$ is also matching covered. Thus a matching covered graph is minimal if and…

Combinatorics · Mathematics 2024-05-28 Yipei Zhang , Xiumei Wang , Jinjiang Yuan , C. T. Ng , T. C. E. Cheng

This paper considers an edge minimization problem in saturated bipartite graphs. An $n$ by $n$ bipartite graph $G$ is $H$-saturated if $G$ does not contain a subgraph isomorphic to $H$ but adding any missing edge to $G$ creates a copy of…

Combinatorics · Mathematics 2021-06-10 Debsoumya Chakraborti , Da Qi Chen , Mihir Hasabnis

For an edge-colored graph $G$, a set $F$ of edges of $G$ is called a \emph{proper cut} if $F$ is an edge-cut of $G$ and any pair of adjacent edges in $F$ are assigned by different colors. An edge-colored graph is \emph{proper disconnected}…

Combinatorics · Mathematics 2019-06-06 Xuqing Bai , You Chen , Meng Ji , Xueliang Li , Yindi Weng , Wenyan Wu

The Small Set Expansion Hypothesis (SSEH) is a conjecture which roughly states that it is NP-hard to distinguish between a graph with a small subset of vertices whose edge expansion is almost zero and one in which all small subsets of…

Computational Complexity · Computer Science 2017-05-11 Pasin Manurangsi

A $ k $-page book drawing of a graph $ G $ is a drawing of $ G $ on $ k $ halfplanes with common boundary $ l $, a line, where the vertices are on $ l $ and the edges cannot cross $ l $. The $ k $-page book crossing number of the graph $ G…

Let $G$ be a graph that admits a perfect matching. A {\sf forcing set} for a perfect matching $M$ of $G$ is a subset $S$ of $M$, such that $S$ is contained in no other perfect matching of $G$. This notion originally arose in chemistry in…

Combinatorics · Mathematics 2009-03-17 Peyman Afshani , Hamed Hatami , Ebadollah S. Mahmoodian