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A good edge-labelling of a simple graph is a labelling of its edges with real numbers such that, for any ordered pair of vertices (u,v), there is at most one nondecreasing path from u to v. Say a graph is good if it admits a good…

Combinatorics · Mathematics 2012-11-13 Abbas Mehrabian

An embedding of a graph on an orientable surface is orientably-regular (or rotary, in an equivalent terminology) if the group of orientation-preserving automorphisms of the embedding is transitive (and hence regular) on incident vertex-edge…

Combinatorics · Mathematics 2023-11-17 Stefan Gyurki , Sona Pavlikova , Jozef Siran

This paper is concerned with the recognition of approximate graph products with respect to the Cartesian product. Most graphs are prime, although they can have a rich product-like structure. The proposed algorithms are based on a local…

Discrete Mathematics · Computer Science 2014-07-14 Marc Hellmuth , Wilfried Imrich , Tomas Kupka

It was recently proved that every planar graph is a subgraph of the strong product of a path and a graph with bounded treewidth. This paper surveys generalisations of this result for graphs on surfaces, minor-closed classes, various…

Combinatorics · Mathematics 2021-02-18 Zdeněk Dvořák , Tony Huynh , Gwenaël Joret , Chun-Hung Liu , David R. Wood

Let $G$ and $H$ be graphs, and $G\boxtimes H$ the strong product of $G$ and $H$. We prove that for any connected graphs $G$ and $H$ there is a strongly connected orientation $D$ of $G\boxtimes H$ such that ${\rm diam}(D)\leq 2r+15$, where…

Combinatorics · Mathematics 2019-11-22 Simon Špacapan , Irena Hrastnik-Ladinek

We investigate the product structure of hereditary graph classes admitting strongly sublinear separators. We characterise such classes as subgraphs of the strong product of a star and a complete graph of strongly sublinear size. In a more…

Combinatorics · Mathematics 2023-09-29 Zdeněk Dvořák , David R. Wood

Let $G$ be a finite group. The co-prime order graph of $G$ is the graph whose vertex set is $G$, and two distinct vertices $x,y$ are adjacent if gcd$(o(x),o(y))$ is either $1$ or a prime, where $o(x)$ and $o(y)$ are the orders of $x$ and…

Combinatorics · Mathematics 2021-09-28 Xuanlong Ma , Zhonghua Wang

A directed graph is set-homogeneous if, whenever U and V are isomorphic finite subdigraphs, there is an automorphism g of the digraph with U^g=V. Here, extending work of Lachlan on finite homogeneous digraphs, we classify finite…

Combinatorics · Mathematics 2010-11-19 Robert Gray , Dugald Macpherson , Cheryl E. Praeger , Gordon F. Royle

A graph $G$ is called well-covered if all maximal independent sets of vertices have the same cardinality. A well-covered graph $G$ is called uniformly well-covered if there is a partition of the set of vertices of $G$ such that each maximal…

Combinatorics · Mathematics 2013-04-12 Rashid Zaare-Nahandi

Mixed graphs can be seen as digraphs with arcs and edges (or digons, that is, two opposite arcs). In this paper, we consider the case where such graphs are bipartite and in which the undirected and directed degrees are one. The best graphs,…

Combinatorics · Mathematics 2024-03-29 C. Dalfó , G. Erskine , G. Exoo , M. A. Fiol , J. Tuite

Several variants of hypergraph products have been introduced as generalizations of the strong and direct products of graphs. Here we show that only some of them are associative. In addition to the Cartesian product, these are the minimal…

Combinatorics · Mathematics 2015-11-24 Richard H. Hammack , Marc Hellmuth , Lydia Ostermeier , Peter F. Stadler

In this paper, we discuss matching extendability of optimal $1$-projective plane graphs (abbreviated as O1PPG), which are drawn on the projective plane $P^2$ so that every edge crosses another edge at most once, and has $n$ vertices and…

Combinatorics · Mathematics 2025-01-16 Shohei Koizumi , Yusuke Suzuki

A graph is said to be well-dominated if all its minimal dominating sets are of the same size. The class of well-dominated graphs forms a subclass of the well studied class of well-covered graphs. While the recognition problem for the class…

Discrete Mathematics · Computer Science 2023-06-22 Didem Gözüpek , Ademir Hujdurović , Martin Milanič

A graph is 1-planar if it can be drawn in the plane such that each edge is crossed at most once. A graph, together with a 1-planar drawing is called 1-plane. Brandenburg et al. showed that there are maximal 1-planar graphs with only…

Combinatorics · Mathematics 2015-09-21 János Barát , Géza Tóth

Let G be a finite group and let Irr(G) be the set of all irreducible complex characters of G. Let cd(G) be the set of all character degrees of G and denote by \rho(G) the set of primes which divide some character degrees of G. The prime…

Group Theory · Mathematics 2013-08-27 Hung P. Tong-Viet

Unigraphs are graphs uniquely determined by their own degree sequence up to isomorphism. There are many subclasses of unigraphs such as threshold graphs, split matrogenic graphs, matroidal graphs, and matrogenic graphs. Unigraphs and these…

Data Structures and Algorithms · Computer Science 2019-04-23 Takashi Horiyama , Jun Kawahara , Shin-ichi Minato , Yu Nakahata

The M-polynomial provides a unifying framework for a wide class of degree-based topological indices. Despite its structural importance, general methods for computing the M-polynomial under graph constructions remain limited. In this paper,…

Combinatorics · Mathematics 2026-03-12 El-Mehdi Mehiri , Sandi Klavžar

A graph $G$ is $\alpha$-excellent if every vertex of $G$ is contained in some maximum independent set of $G$. In this paper, we characterize $\alpha$-excellent bipartite graphs, $\alpha$-excellent unicyclic graphs, $\alpha$-excellent…

Combinatorics · Mathematics 2022-08-19 M. Dettlaff , M. A. Henning , J. Topp

Planar graphs can be represented as intersection graphs of different types of geometric objects in the plane, e.g., circles (Koebe, 1936), line segments (Chalopin \& Gon{\c{c}}alves, 2009), \textsc{L}-shapes (Gon{\c{c}}alves et al, 2018).…

Computational Geometry · Computer Science 2021-06-03 Dibyayan Chakraborty , Kshitij Gajjar

In this paper we determine partial answers to the question given in the title, thereby significantly extending results of Broere and Hattingh. We characterize completely those pairs of complete graphs whose tensor products are circulant. We…

Combinatorics · Mathematics 2007-05-23 J. C. George , R. S. Sanders
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