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Many important theorems in combinatorics, such as Szemer\'edi's theorem on arithmetic progressions and the Erd\H{o}s-Stone Theorem in extremal graph theory, can be phrased as statements about independent sets in uniform hypergraphs. In…

Combinatorics · Mathematics 2014-03-24 József Balogh , Robert Morris , Wojciech Samotij

Szemer\'edi's regularity lemma is a fundamental tool in extremal combinatorics. However, the original version is only helpful in studying dense graphs. In the 1990s, Kohayakawa and R\"odl proved an analogue of Szemer\'edi's regularity lemma…

Combinatorics · Mathematics 2015-10-26 David Conlon , Jacob Fox , Yufei Zhao

A common theme in many extremal problems in graph theory is the relation between local and global properties of graphs. One of the most celebrated results of this type is the Ruzsa-Szemer\'edi triangle removal lemma, which states that if a…

Combinatorics · Mathematics 2016-12-01 Lior Gishboliner , Asaf Shapira

We develop a new method for constructing approximate decompositions of dense graphs into sparse graphs and apply it to longstanding decomposition problems. For instance, our results imply the following. Let $G$ be a quasi-random $n$-vertex…

Combinatorics · Mathematics 2017-09-28 Jaehoon Kim , Daniela Kühn , Deryk Osthus , Mykhaylo Tyomkyn

We study quantitative relationships between the triangle removal lemma and several of its variants. One such variant, which we call the triangle-free lemma, states that for each $\epsilon>0$ there exists $M$ such that every triangle-free…

Combinatorics · Mathematics 2022-01-17 Jacob Fox , Yufei Zhao

We study the integral and measure theory of the ultraproduct of finite sets. As a main application we construct limit objects for hypergraph sequences. We give a new proof for the Hypergraph Removal Lemma and the Hypergraph Regularity…

Combinatorics · Mathematics 2007-05-23 Gabor Elek , Balazs Szegedy

The celebrated Green-Tao theorem states that there are arbitrarily long arithmetic progressions in the primes. One of the main ingredients in their proof is a relative Szemer\'edi theorem which says that any subset of a pseudorandom set of…

Number Theory · Mathematics 2015-10-26 David Conlon , Jacob Fox , Yufei Zhao

The well-known regularity lemma of E. Szemer\'edi for graphs (i.e. 2-uniform hypergraphs) claims that for any graph there exists a vertex partition with the property of quasi-randomness. We give a simple construction of such a partition. It…

Combinatorics · Mathematics 2009-05-01 Yoshiyasu Ishigami

We obtain a hypergraph generalisation of the graph blow-up lemma proved by Komlos, Sarkozy and Szemeredi, showing that hypergraphs with sufficient regularity and no atypical vertices behave as if they were complete for the purpose of…

Combinatorics · Mathematics 2010-11-08 Peter Keevash

Szemer\'edi's regularity lemma is a basic tool in graph theory, and also plays an important role in additive combinatorics, most notably in proving Szemer\'edi's theorem on arithmetic progressions . In this note we revisit this lemma from…

Combinatorics · Mathematics 2007-05-23 Terence Tao

A recent result of Alon, Ben-Eliezer and Fischer establishes an induced removal lemma for ordered graphs. That is, if $F$ is an ordered graph and $\varepsilon>0$, then there exists $\delta_{F}(\varepsilon)>0$ such that every $n$-vertex…

Combinatorics · Mathematics 2023-03-13 Lior Gishboliner , István Tomon

The Tur\'{a}n number of a graph $H$, denoted $\mbox{ex}(n,H)$, is the maximum number of edges in an $n$-vertex graph with no subgraph isomorphic to $H$. Solymosi conjectured that if $H$ is any graph and $\mbox{ex}(n,H) = O(n^{\alpha})$…

Combinatorics · Mathematics 2013-12-12 Craig Timmons , Jacques Verstraete

Let $k\geq 2$ and fix a $k$-uniform hypergraph $\mathcal{F}$. Consider the random process that, starting from a $k$-uniform hypergraph $\mathcal{H}$ on $n$ vertices, repeatedly deletes the edges of a copy of $\mathcal{F}$ chosen uniformly…

Combinatorics · Mathematics 2025-08-05 Felix Joos , Marcus Kühn

Motivated by problems on random differences in Szemer\'{e}di's theorem and on large deviations for arithmetic progressions in random sets, we prove upper bounds on the Gaussian width of point sets that are formed by the image of the…

Combinatorics · Mathematics 2018-10-22 Jop Briët , Sivakanth Gopi

In this note, we obtain a quantitative improvement on the hypergraph variant of the Balog-Szemer\'{e}di-Gowers theorem due to Sudakov, Szemer\'{e}di, and Vu [Duke Math. J.129.1 (2005): 129--155]. Additionally, we prove the hypergraph…

Combinatorics · Mathematics 2025-03-27 Hyunwoo Lee

Suppose one needs to change the direction of at least $\epsilon n^2$ edges of an $n$-vertex tournament $T$, in order to make it $H$-free. A standard application of the regularity method shows that in this case $T$ contains at least…

Combinatorics · Mathematics 2017-10-17 Jacob Fox , Lior Gishboliner , Asaf Shapira , Raphael Yuster

While Szemer\'edi's graph regularity lemma is an indispensable tool for studying extremal problems in graph theory, using it comes with a hefty price, since a worst-case graph may only have regular partitions of tower-type size. It is thus…

Combinatorics · Mathematics 2025-08-14 Lior Gishboliner , Asaf Shapira , Yuval Wigderson

An old and well-known conjecture of Frankl and F\"{u}redi states that the Lagrangian of an $r$-uniform hypergraph with $m$ edges is maximised by an initial segment of colex. In this paper we disprove this conjecture by finding an infinite…

Combinatorics · Mathematics 2020-03-03 Vytautas Gruslys , Shoham Letzter , Natasha Morrison

Green [Geometric and Functional Analysis 15 (2005), 340--376] established a version of the Szemer\'edi Regularity Lemma for abelian groups and derived the Removal Lemma for abelian groups as its corollary. We provide another proof of his…

Combinatorics · Mathematics 2008-05-01 Daniel Král' , Oriol Serra , Lluís Vena

As an application of Szemeredi's regularity lemma, Erdos-Frankl-Rodl (1986) showed that the number of graphs on vertex set {1,2,...n} with a monotone class P is $2^{(1+o(1))ex(n,P)n^2/2}$ where $ex(n,P)$ is the maximum number of edges of an…

Combinatorics · Mathematics 2007-12-05 Yoshiyasu Ishigami