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A coloured graph is k-ultrahomogeneous if every isomorphism between two induced subgraphs of order at most k extends to an automorphism. A coloured graph is t-tuple regular if the number of vertices adjacent to every vertex in a set S of…

Combinatorics · Mathematics 2021-02-23 Irene Heinrich , Thomas Schneider , Pascal Schweitzer

A graph $H$ is common if the number of monochromatic copies of $H$ in a 2-edge-colouring of the complete graph $K_n$ is asymptotically minimised by the random colouring. We prove that, given $k,r>0$, there exists a $k$-connected common…

Combinatorics · Mathematics 2023-06-14 Sejin Ko , Joonkyung Lee

A graph is called uniquely distinguishing colorable if there is only one partition of vertices of the graph that forms distinguishing coloring with the smallest possible colors. In this paper, we study the unique colorability of the…

Combinatorics · Mathematics 2023-08-16 M. Korivand , N. Soltankhah , K. Khashyarmanesh

We show that the $f$-vector of Galashin's poset associahedron $\mathscr A(P)$ only depends on the comparability graph of $P$. In particular, this allows us to produce a family of polytopes with the same $f$-vectors as permutohedra, but that…

Combinatorics · Mathematics 2023-10-03 Son Nguyen , Andrew Sack

Let G be a plane graph with maximum face size D. If all faces of G with size four or more are vertex disjoint, then G has a cyclic coloring with D+1 colors, i.e., a coloring such that all vertices incident with the same face receive…

Combinatorics · Mathematics 2008-11-18 Jernej Azarija , Daniel Král' , Rok Erman , Matjaz Krnc , Ladislav Stacho

A path in an edge-colored graph is said to be a rainbow path if no two edges on the path have the same color. An edge-colored graph is (strongly) rainbow connected if there exists a rainbow (geodesic) path between every pair of vertices.…

Computational Complexity · Computer Science 2011-09-28 Shasha Li , Xueliang Li

For a graph G, we define a small automorphism as one that maps some vertex into its neighbour. We investigate the edge colourings of G that break every small automorphism of G. We show that such a colouring can be chosen from any set of…

Combinatorics · Mathematics 2023-06-22 Jakub Kwaśny , Marcin Stawiski

An edge-colored graph $G$ is rainbow connected if any two vertices are connected by a path whose edges have distinct colors. The rainbow connection number of a connected graph $G$, denoted $rc(G)$, is the smallest number of colors that are…

Combinatorics · Mathematics 2011-12-05 Arash Ahadi , Ali Dehghan

We describe a new sequence of polytopes which characterize A_infinity maps from a topological monoid to an A_infinity space. Therefore each of these polytopes is a quotient of the corresponding multiplihedron. Later term(s) in our sequence…

Category Theory · Mathematics 2008-05-08 Stefan Forcey

The arc graph $\delta(G)$ of a digraph $G$ is the digraph with the set of arcs of $G$ as vertex-set, where the arcs of $\delta(G)$ join consecutive arcs of $G$. In 1981, Poljak and R\"{o}dl characterised the chromatic number of $\delta(G)$…

Combinatorics · Mathematics 2016-10-06 Danny Rorabaugh , Claude Tardif , David Wehlau , Imed Zaguia

The (torsion) complexity of a finite signed graph is defined to be the order of the torsion subgroup of the abelian group presented by its Laplacian matrix. When $G$ is $d$-periodic (i.e., $G$ has a free ${\mathbb Z}^d$-action by graph…

Geometric Topology · Mathematics 2020-08-14 Daniel S. Silver , Susan G. Williams

Building on recent work of Robertson and Steger, we associate a C*-algebra to a combinatorial object which may be thought of as a higher rank graph. This C*-algebra is shown to be isomorphic to that of the associated path groupoid.…

Operator Algebras · Mathematics 2007-05-23 Alex Kumjian , David Pask

Consider a bicolored point set $P$ in general position in the plane consisting of $n$ blue and $n$ red points. We show that if a subset of the red points forms the vertices of a convex polygon separating the blue points, lying inside the…

Combinatorics · Mathematics 2024-04-10 Jan Soukup

A coloring of vertices of a given graph is called perfect if the color structure of each ball of radius $1$ in the graph depends only on the color of the ball center. Let $n$ be a positive integer. We consider a lexicographic product of the…

Combinatorics · Mathematics 2021-08-03 M. A. Lisitsyna , S. V. Avgustinovich , O. G. Parshina

An outerplanar graph is a planar graph that has a planar drawing with all vertices on the unbounded face. The matching complex of a graph is the simplicial complex whose faces are subsets of disjoint edges of the graph. In this paper we…

Combinatorics · Mathematics 2024-11-08 Margaret Bayer , Marija Jelić Milutinović , Julianne Vega

A fullerene graph is a planar cubic 3-connected graph with only pentagonal and hexagonal faces. We show that fullerene graphs have exponentially many perfect matchings.

Combinatorics · Mathematics 2010-05-28 Frantisek Kardos , Daniel Král' , Jozef Miskuf , Jean-Sébastien Sereni

The pseudoachromatic index of a graph is the maximum number of colors that can be assigned to its edges, such that each pair of different colors is incident to a common vertex. If for each vertex its incident edges have different color,…

Combinatorics · Mathematics 2018-09-26 O. Aichholzer , G. Araujo-Pardo , N. García-Colín , T. Hackl , D. Lara , C. Rubio-Montiel , J. Urrutia

We prove that if $H$ is a subgraph of a complete multipartite graph $G$, then $H$ contains a connected component $H'$ satisfying $|E(H')||E(G)|\geq |E(H)|^2$. We use this to prove that every three-coloring of the edges of a complete graph…

Combinatorics · Mathematics 2022-08-30 Sammy Luo

A distinguishing coloring of a graph is a vertex coloring such that only the identity automorphism of the graph preserves the coloring. A 2-distinguishable graph is a graph which can be distinguished using 2 colors. The cost $\rho(G)$ of a…

Combinatorics · Mathematics 2025-06-04 Alexa Gopaulsingh , Zalán Molnár , Amitayu Banerjee

We present a graph model for a background independent, relational approach to spacetime emergence. The general idea and the graph main features, detailed in [1], are discussed. This is a combinatorial (dynamical) metric graph, colored on…

General Relativity and Quantum Cosmology · Physics 2020-07-14 D. Pugliese