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Nowhere dense classes of graphs are classes of sparse graphs with rich structural and algorithmic properties, however, they fail to capture even simple classes of dense graphs. Monadically stable classes, originating from model theory,…

Discrete Mathematics · Computer Science 2022-06-30 Jan Dreier , Nikolas Mählmann , Amer E. Mouawad , Sebastian Siebertz , Alexandre Vigny

Consider the following Ramsey game played on the edge set of $K_{\mathbb N}$. In every round, Builder selects an edge and Painter colours it red or blue. Builder's goal is to force Painter to create a red copy of a path $P_k$ on $k$…

Combinatorics · Mathematics 2023-10-17 Małgorzata Bednarska-Bzdȩga

The Ramsey number $r(G,H)$ is the minimum $N$ such that every graph on $N$ vertices contains $G$ as a subgraph or its complement contains $H$ as a subgraph. For integers $n \geq k \geq 1$, the $k$-book $B_{k,n}$ is the graph on $n$ vertices…

Combinatorics · Mathematics 2023-07-17 Jacob Fox , Xiaoyu He , Yuval Wigderson

An ordered graph $\mathcal{G}$ is a simple graph together with a total ordering on its vertices. The (2-color) Ramsey number of $\mathcal{G}$ is the smallest integer $N$ such that every 2-coloring of the edges of the complete ordered graph…

Combinatorics · Mathematics 2019-02-26 Jesse Geneson , Amber Holmes , Xujun Liu , Dana Neidinger , Yanitsa Pehova , Isaac Wass

We consider a generalisation of the classical Ramsey theory setting to a setting where each of the edges of the underlying host graph is coloured with a {\em set} of colours (instead of just one colour). We give bounds for monochromatic…

Combinatorics · Mathematics 2018-05-30 Sebastián Bustamante , Maya Stein

We give asymptotically optimal constructions in generalized Ramsey theory using results about conflict-free hypergraph matchings. For example, we present an edge-coloring of $K_{n,n}$ with $2n/3 + o(n)$ colors such that each $4$-cycle…

Combinatorics · Mathematics 2022-08-29 Felix Joos , Dhruv Mubayi

We study the multicolor Ramsey numbers for paths and even cycles, $R_k(P_n)$ and $R_k(C_n)$, which are the smallest integers $N$ such that every coloring of the complete graph $K_N$ has a monochromatic copy of $P_n$ or $C_n$ respectively.…

Combinatorics · Mathematics 2018-01-15 Charlotte Knierim , Pascal Su

In this work, we give several new upper and lower bounds on Ramsey numbers for books and wheels, including a tight upper bound establishing $R(W_5, W_7) = 15$, matching upper and lower bounds giving $R(W_5, W_9) = 18$, $R(B_2, B_8) = 21$,…

Combinatorics · Mathematics 2026-02-17 Bernard Lidický , Gwen McKinley , Florian Pfender , Steven Van Overberghe

We extend two well-known results in Ramsey theory from from $K_n$ to arbitrary $n$-chromatic graphs. The first is a note of Erd\H os and Rado stating that in every 2-coloring of the edges of $K_n$ there is a monochromatic tree on $n$…

Combinatorics · Mathematics 2015-06-16 Arie Bialostocki , Andras Gyarfas

In this paper, we study Ramsey-type problems for directed graphs. We first consider the $k$-colour oriented Ramsey number of $H$, denoted by $\overrightarrow{R}(H,k)$, which is the least $n$ for which every $k$-edge-coloured tournament on…

Combinatorics · Mathematics 2019-05-03 Matija Bucic , Shoham Letzter , Benny Sudakov

Let $r(G,H)$ be the smallest integer $N$ such that for any $2$-coloring (say, red and blue) of the edges of $K\_n$, $n\geqslant N$, there is either a red copy of $G$ or a blue copy of $H$. Let $K\_n-K\_{1,s}$ be the complete graph on $n$…

Combinatorics · Mathematics 2016-04-01 Jonathan Chappelon , Luis Pedro Montejano , Jorge Ramírez Alfonsín

We show that for every finite colouring of the natural numbers there exists $a,b >1$ such that the triple $\{a,b,a^b\}$ is monochromatic. We go on to show the partition regularity of a much richer class of patterns involving exponentiation.…

Combinatorics · Mathematics 2016-10-24 Julian Sahasrabudhe

A Gallai coloring is a coloring of the edges of a complete graph without rainbow triangles, and a Gallai $k$-coloring is a Gallai coloring that uses $k$ colors. We study Ramsey-type problems in Gallai colorings. Given an integer $k\ge1$ and…

Combinatorics · Mathematics 2018-04-03 Christian Bosse , Zi-Xia Song

We study Ramsey-type problems in Gallai-colorings. Given a graph $G$ and an integer $k\ge1$, the Gallai-Ramsey number $gr_k(K_3,G)$ is the least positive integer $n$ such that every $k$-coloring of the edges of the complete graph on $n$…

Combinatorics · Mathematics 2017-10-03 Christian Bosse , Zi-Xia Song

Given a graph $G$, its Ramsey number $r(G)$ is the minimum $N$ so that every two-coloring of $E(K_N)$ contains a monochromatic copy of $G$. It was conjectured by Conlon, Fox, and Sudakov that if one deletes a single vertex from $G$, the…

Combinatorics · Mathematics 2024-01-17 Yuval Wigderson

Ramsey-type problems for linear equations began with Schur's theorem and were systematically generalized by Richard Rado. In the off-diagonal framework for two colors, one considers two different linear equations…

Combinatorics · Mathematics 2026-03-02 Rajat Adak , Yash Bakshi , L. Sunil Chandran , Saraswati Girish Nanoti

Gy\'arf\'as, S\'ark\"ozy and Szemer\'edi proved that the $2$-color Ramsey number $R(\mathcal{C}^k_n,\mathcal{C}^k_n)$ of a $k$-uniform loose cycle $\mathcal{C}^k_n$ is asymptotically $\frac{1}{2}(2k-1)n,$ generating the same result for…

Combinatorics · Mathematics 2016-06-14 Gholamreza Omidi , Maryam Shahsiah

We determine the $2$-color Ramsey number of a {\em connected} triangle matching $c(nK_3)$ which is any connected graph containing $n$ vertex disjoint triangles. We obtain that $R(c(nK_3),c(nK_3))=7n-2$, somewhat larger than in the classical…

Combinatorics · Mathematics 2015-09-21 Andras Gyarfas , Gabor N. Sarkozy

Recently, determining the Ramsey numbers of loose paths and cycles in uniform hypergraphs has received considerable attention. It has been shown that the $2$-color Ramsey number of a $k$-uniform loose cycle $\mathcal{C}^k_n$,…

Combinatorics · Mathematics 2016-02-18 Gholamreza Omidi , Maryam Shahsiah

For given graphs $G_{1}, G_{2}, ... , G_{k}, k \geq 2$, the multicolor Ramsey number $R(G_{1}, G_{2}, ... , G_{k})$ is the smallest integer $n$ such that if we arbitrarily color the edges of the complete graph of order $n$ with $k$ colors,…

Combinatorics · Mathematics 2017-07-24 Farideh Khoeini , Tomasz Dzido