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The harmonious chromatic number of a graph $G$ is the minimum number of colors that can be assigned to the vertices of $G$ in a proper way such that any two distinct edges have different color pairs. This paper gives various results on…

For given simple graphs $G_1$ and $G_2$, the size Ramsey number $\hat{R}(G_1,G_2)$ is the smallest positive integer $m$, where there exists a graph $G$ with $m$ edges such that in any edge coloring of $G$ with two colors red and blue, there…

Combinatorics · Mathematics 2017-02-07 Ramin Javadi , Gholamreza Omidi

We say that a graph $F$ strongly arrows a pair of graphs $(G,H)$ if any 2-colouring of its edges with red and blue leads to either a red $G$ or a blue $H$ appearing as induced subgraphs of $F$. The induced Ramsey number, $IR(G,H)$ is…

Combinatorics · Mathematics 2017-10-30 Izolda Gorgol

An edge-colored graph is called \textit{rainbow graph} if all the colors on its edges are distinct. For a given positive integer $n$ and a family of graphs $\mathcal{G}$, the anti-Ramsey number $ar(n, \mathcal{G})$ is the smallest number of…

Combinatorics · Mathematics 2024-11-20 Wenke Liu , Hongliang Lu , Xinyue Luo

For a graph G and an integer t we let mcc_t(G) be the smallest m such that there exists a coloring of the vertices of G by t colors with no monochromatic connected subgraph having more than m vertices. Let F be any nontrivial minor-closed…

Combinatorics · Mathematics 2007-05-23 N. Linial , J. Matousek , O. Sheffet , G. Tardos

For graphs $F$ and $G$, let $F\to G$ signify that any red/blue edge coloring of $F$ contains a monochromatic $G$. Denote by ${\cal G}(N,p)$ the random graph space of order $N$ and edge probability $p$. Using the regularity method, one can…

Combinatorics · Mathematics 2021-11-03 Ye Wang , Yusheng Li

Let $n,r,k,s$ be positive integers with $n,k\ge 2$. The generalized Ramsey number $R(n,r;k,s)$ is the smallest positive integer $p$ such that for every graph $G$ of order $p$, either $G$ contains a subgraph induced by $n$ vertices with at…

Combinatorics · Mathematics 2014-11-06 Zhi-Hong Sun

Given a pair of graphs $G$ and $H$, the Ramsey number $R(G,H)$ is the smallest $N$ such that every red-blue coloring of the edges of the complete graph $K_N$ contains a red copy of $G$ or a blue copy of $H$. If a graph $G$ is connected, it…

Combinatorics · Mathematics 2018-07-09 Alexey Pokrovskiy , Benny Sudakov

The classical hypergraph Ramsey number $r_k(s,n)$ is the minimum $N$ such that for every red-blue coloring of the $k$-tuples of $\{1,\ldots, N\}$, there are $s$ integers such that every $k$-tuple among them is red, or $n$ integers such that…

Combinatorics · Mathematics 2018-05-08 Dhruv Mubayi , Andrew Suk

The induced Ramsey number $r_{\mathrm{ind}}(F)$ of a $k$-uniform hypergraph $F$ is the smallest natural number $n$ for which there exists a $k$-uniform hypergraph $G$ on $n$ vertices such that every two-coloring of the edges of $G$ contains…

Combinatorics · Mathematics 2017-11-01 David Conlon , Domingos Dellamonica , Steven La Fleur , Vojtěch Rödl , Mathias Schacht

The induced Ramsey number $R_{\mathrm{ind}}(H; r)$ of a graph $H$ is the minimum number $N$ such that there exists a graph with $N$ vertices for which all $r$-colourings of its edges contain a monochromatic induced copy of $H$. Our main…

Combinatorics · Mathematics 2025-11-14 Lucas Aragão , Marcelo Campos , Gabriel Dahia , Rafael Filipe , João Pedro Marciano

An $n$-vertex graph is called $C$-Ramsey if it has no clique or independent set of size $C\log_2 n$ (i.e., if it has near-optimal Ramsey behavior). In this paper, we study edge-statistics in Ramsey graphs, in particular obtaining very…

Combinatorics · Mathematics 2024-05-31 Matthew Kwan , Ashwin Sah , Lisa Sauermann , Mehtaab Sawhney

In the online graph coloring problem, vertices from a graph G, known in advance, arrive in an online fashion and an algorithm must immediately assign a color to each incoming vertex v so that the revealed graph is properly colored. The…

Computational Complexity · Computer Science 2017-06-27 Martin Böhm , Pavel Veselý

In Ramsey theory for graphs we are given a graph $G$ and we are required to find the least $n_0$ such that, for any $n\geq n_0$, any red/blue colouring of the edges of $K_n$ gives a subgraph $G$ all of whose edges are blue or all are red.…

Combinatorics · Mathematics 2020-01-23 Yair Caro , Josef Lauri , Christina Zarb

Let $R(C_n)$ be the Ramsey number of the cycle on $n$ vertices. We prove that, for some $C > 0$, with high probability every $2$-colouring of the edges of $G(N,p)$ has a monochromatic copy of $C_n$, as long as $N\geq R(C_n) + C/p$ and $p…

Combinatorics · Mathematics 2024-08-22 Pedro Araújo , Matías Pavez-Signé , Nicolás Sanhueza-Matamala

For two graphs, $G$, and $H$, an edge-coloring of a complete graph is $(G,H)$-good if there is no monochromatic subgraph isomorphic to $G$ and no rainbow subgraph isomorphic to $H$ in this coloring. The set of number of colors used by some…

Combinatorics · Mathematics 2010-05-18 Maria Axenovich , JiHyeok Choi

For given graphs $G_1,\ldots,G_k$, the size-Ramsey number $\hat{R}(G_1,\ldots,G_k)$ is the smallest integer $m$ for which there exists a graph $H$ on $m$ edges such that in every $k$-edge coloring of $H$ with colors $1,\ldots,k$, $ H $…

Combinatorics · Mathematics 2017-01-26 Ramin Javadi , Farideh Khoeini , Gholam Reza Omidi , Alexey Pokrovskiy

We prove that for all graphs with at most $(3.75-o(1))n$ edges there exists a 2-coloring of the edges such that every monochromatic path has order less than $n$. This was previously known to be true for graphs with at most $2.5n-7.5$ edges.…

Combinatorics · Mathematics 2021-11-05 Deepak Bal , Louis DeBiasio

Ramsey's theorem states that for all finite colorings of an infinite set, there exists an infinite homogeneous subset. What if we seek a homogeneous subset that is also order-equivalent to the original set? Let $S$ be a linearly ordered set…

Combinatorics · Mathematics 2025-11-11 Joanna Boyland , William Gasarch , Nathan Hurtig , Robert Rust

For a graph $G=(V,E)$, a hypergraph $\mathcal{H}$ is called a Berge-$G$, denoted by $BG$, if there exists a bijection $f: E(G) \to E(\mathcal{H})$ such that for every $e \in E(G)$, $e \subseteq f(e)$. Let the Ramsey number $R^r(BG,BG)$ be…

Combinatorics · Mathematics 2019-11-13 Nika Salia , Casey Tompkins , Zhiyu Wang , Oscar Zamora
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