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Given an integer $c\in \mathbb{N}$, we say a graph $G$ is $c$-pinched if $G$ does not contain an induced subgraph consisting of $c$ cycles, all going through a single common vertex and otherwise pairwise disjoint and with no edges between…

Combinatorics · Mathematics 2025-04-08 Bogdan Alecu , Maria Chudnovsky , Sepehr Hajebi , Sophie Spirkl

The problem of Zarankiewicz asks for the maximum number of edges in a bipartite graph on $n$ vertices which does not contain the complete bipartite graph $K_{k,k}$ as a subgraph. A classical theorem due to K\H{o}v\'ari, S\'os, and Tur\'an…

Combinatorics · Mathematics 2021-04-05 Oliver Janzer , Cosmin Pohoata

We prove an infinite Ramsey theorem for noncommutative graphs realized as unital self-adjoint subspaces of linear operators acting on an infinite dimensional Hilbert space. Specifically, we prove that if V is such a subspace, then provided…

Operator Algebras · Mathematics 2017-11-28 Matthew Kennedy , Taras Kolomatski , Daniel Spivak

The Prague dimension of a graph $G$ is defined as the minimum number of complete graphs whose direct product contains $G$ as an induced subgraph. Introduced in the 1970s by Ne\v{s}et\v{r}il, Pultr, and R\"odl -- and motivated by the work of…

Combinatorics · Mathematics 2025-12-10 Felix Joos , Letícia Mattos

A beautiful conjecture of Erd\H{o}s-Simonovits and Sidorenko states that if H is a bipartite graph, then the random graph with edge density p has in expectation asymptotically the minimum number of copies of H over all graphs of the same…

Combinatorics · Mathematics 2010-06-09 David Conlon , Jacob Fox , Benny Sudakov

For any countably infinite graph $G$, Ramsey's theorem guarantees an infinite monochromatic copy of $G$ in any $r$-coloring of the edges of the countably infinite complete graph $K_\mathbb{N}$. Taking this a step further, it is natural to…

Combinatorics · Mathematics 2018-08-16 Louis DeBiasio , Paul McKenney

The paper systematically classifies rings based on the dominant metric dimensions (Ddim) of their associated CZDG, establishing consequential bounds for the Ddim of these compressed zero-divisor graphs. The authors investigate the interplay…

Commutative Algebra · Mathematics 2024-05-09 Nasir Ali , Hafiz Muhammad Afzal Siddiqui , Muhammad Imran Qureshi

The Bandwidth Theorem of B\"ottcher, Schacht and Taraz [Mathematische Annalen 343 (1), 175-205] gives minimum degree conditions for the containment of spanning graphs H with small bandwidth and bounded maximum degree. We generalise this…

Combinatorics · Mathematics 2013-05-10 Julia Böttcher , Anusch Taraz , Andreas Würfl

A graph $\mathcal{H}=(W,E_\mathcal{H})$ is said to have {\em bandwidth} at most $b$ if there exists a labeling of $W$ as $w_1,w_2,\dots,w_n$ such that $|i-j|\leq b$ for every edge $w_iw_j\in E_\mathcal{H}$. We say that $\mathcal{H}$ is a…

Combinatorics · Mathematics 2022-03-16 Chunlin You , Qizhong Lin

We show that for every two cycles $C,D$, there exists $c>0$ such that if $G$ is both $C$-free and $\overline{D}$-free then $G$ has a clique or stable set of size at least $|G|^c$. ("$H$-free" means with no induced subgraph isomorphic to…

Combinatorics · Mathematics 2024-06-21 Tung Nguyen , Alex Scott , Paul Seymour

Burr and Erd\H{o}s in 1975 conjectured, and Chv\'atal, R\"odl, Szemer\'edi and Trotter later proved, that the Ramsey number of any bounded degree graph is linear in the number of vertices. In this paper, we disprove the natural directed…

Combinatorics · Mathematics 2022-01-25 Jacob Fox , Xiaoyu He , Yuval Wigderson

We prove that for every complete multipartite graph $F$ there exist very dense graphs $G_n$ on $n$ vertices, namely with as many as ${n\choose 2}-cn$ edges for all $n$, for some constant $c=c(F)$, such that $G_n$ can be decomposed into…

Combinatorics · Mathematics 2015-01-16 Csilla Bujtás , Zsolt Tuza

We prove the Erd\H{o}s-Hajnal conjecture for the five-vertex path $P_5$; that is, there exists $c>0$ such that every $n$-vertex graph with no induced $P_5$ has a clique or stable set of size at least $n^c$. This completes the verification…

Combinatorics · Mathematics 2026-02-25 Tung Nguyen , Alex Scott , Paul Seymour

We consider a variation of Ramsey numbers introduced by Erd\H{o}s and Pach (1983), where instead of seeking complete or independent sets we only seek a $t$-homogeneous set, a vertex subset that induces a subgraph of minimum degree at least…

Combinatorics · Mathematics 2017-07-19 Ross J. Kang , János Pach , Viresh Patel , Guus Regts

Size-Ramsey numbers are a central notion in combinatorics and have been widely studied since their introduction by Erd\H{o}s, Faudree, Rousseau and Schelp in 1978. Research has mainly focused on the size-Ramsey numbers of $n$-vertex graphs…

Combinatorics · Mathematics 2023-09-06 Nemanja Draganić , Marc Kaufmann , David Munhá Correia , Kalina Petrova , Raphael Steiner

We show that, for every $r, k$, there is an $n = n(r,k)$ so that any $r$-coloring of the edges of the complete graph on $[n]$ will yield a monochromatic complete subgraph on vertices ${a + \sum_{i \in I} d_i \mid I \subseteq [k]}$ for some…

Combinatorics · Mathematics 2012-03-01 Andy Parrish

Let $\Gamma$ be a $G$-symmetric graph with vertex set $V$. We suppose that $V$ admits a $G$-partition $\mathcal{B} = \{ B_0, ... , B_b \}$, with parts of size $v$, and that the quotient graph induced on $\mathcal B$ is a complete graph of…

Combinatorics · Mathematics 2017-09-06 A. Gardiner , Cheryl E. Praeger

An old conjecture of Erd\H{o}s and McKay states that if all homogeneous sets in an $n$-vertex graph are of order $O(\log n)$ then the graph contains induced subgraphs of each size from $\{0,1,\ldots, \Omega (n^2)\}$. We prove a bipartite…

Combinatorics · Mathematics 2022-11-09 Eoin Long , Laurentiu Ploscaru

Using techniques in \cite{chudnovsky2023erdHos} and substitution in \cite{alon2001ramsey}, we show that there is $\epsilon>0$ such that for any graph $G$ with VC-dimension $\leq 2$, $G$ has a clique or an anti-clique of size $\geq…

Logic · Mathematics 2023-10-27 Yayi Fu

Given positive integers $k$ and $\ell$ we write $G \rightarrow (K_k,K_\ell)$ if every 2-colouring of the edges of $G$ yields a red copy of $K_k$ or a blue copy of $K_\ell$ and we denote by $R(k)$ the minimum $n$ such that $K_n\rightarrow…

Combinatorics · Mathematics 2025-11-06 Walner Mendonça , Meysam Miralaei , Guilherme O. Mota