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Aboulker et al. proved that a digraph with large enough dichromatic number contains any fixed digraph as a subdivision. The dichromatic number of a digraph is the smallest order of a partition of its vertex set into acyclic induced…

Combinatorics · Mathematics 2024-05-24 Lucas Picasarri-Arrieta , Clément Rambaud

We prove that for every graph H and for every integer s, the class of graphs that do not contain K_s, K_{s,s}, or any subdivision of H as an induced subgraph has bounded expansion; this strengthens a result of Kuhn and Osthus. The argument…

Combinatorics · Mathematics 2017-06-20 Zdeněk Dvořák

We determine, for all $k\geq 6$, the typical structure of graphs that do not contain an induced $2k$-cycle. This verifies a conjecture of Balogh and Butterfield. Surprisingly, the typical structure of such graphs is richer than that…

Combinatorics · Mathematics 2015-07-20 Jaehoon Kim , Daniela Kühn , Deryk Osthus , Timothy Townsend

Directed graphs occur throughout statistical modeling of networks, and exchangeability is a natural assumption when the ordering of vertices does not matter. There is a deep structural theory for exchangeable undirected graphs, which…

Statistics Theory · Mathematics 2016-12-19 Diana Cai , Nathanael Ackerman , Cameron Freer

We determine to within a constant factor the threshold for the property that two random k-uniform hypergraphs with edge probability p have an edge-disjoint packing into the same vertex set. More generally, we allow the hypergraphs to have…

Combinatorics · Mathematics 2016-03-01 Béla Bollobás , Svante Janson , Alex Scott

A conjecture of Jackson from 1981 states that every $d$-regular oriented graph on $n$ vertices with $n\leq 4d+1$ is Hamiltonian. We prove this conjecture for sufficiently large $n$. In fact we prove a more general result that for all…

Combinatorics · Mathematics 2025-04-30 Allan Lo , Viresh Patel , Mehmet Akif Yıldız

Let $D$ be a digraph of order $p\geq5$ with minimum degree at least $p-1$ and with minimum semi-degree at least $p/2-1$. In his excellent and renowned paper, ``Long Cycles in Digraphs" (Proc. London Mathematical Society (3), 42 (1981),…

Combinatorics · Mathematics 2025-10-31 Samvel Kh. Darbinyan

We show that $k$-uniform hypergraphs on $n$ vertices whose codegree is at least $(2/3 + o(1))n$ can be decomposed into tight cycles, subject to the trivial divisibility conditions. As a corollary, we show those graphs contain tight Euler…

Combinatorics · Mathematics 2024-03-07 Allan Lo , Simón Piga , Nicolás Sanhueza-Matamala

The famous Brown-Erd\H{o}s-S\'os conjecture from 1973 states, in an equivalent form, that for any fixed $\delta>0$ and integer $k\geq 3$ every sufficiently large linear $3$-uniform hypergraph of size $\delta n^2$ contains some $k$ edges…

Combinatorics · Mathematics 2025-08-14 Giovanne Santos , Mykhaylo Tyomkyn

We generalize the fact that graphs with small VC-dimension can be approximated by rectangles, showing that hypergraphs with small VC_k-dimension (equivalently, omitting a fixed finite (k+1)-partite (k+1)-uniform hypergraph) can be…

Combinatorics · Mathematics 2020-10-05 Artem Chernikov , Henry Towsner

A recent paper by the authors (ITCS'26) initiates the study of the Triangle Detection problem in graphs avoiding a fixed pattern $H$ as a subgraph and proposes a \emph{dichotomy hypothesis} characterizing which patterns $H$ make the…

Data Structures and Algorithms · Computer Science 2026-02-27 Amir Abboud , Ron Safier , Nathan Wallheimer

Let $Y_{1}, \ldots, Y_{q}$ be closed subschemes which are located in $\ell$-subgeneral position with index $\kappa$ in a complex projective variety $X$ of dimension $n.$ Let $A$ be an ample Cartier divisor on $X.$ We obtain that if a…

Algebraic Geometry · Mathematics 2023-12-27 Liang Wang , Tingbin Cao , Hongzhe Cao

Erd\H{o}s and Hajnal conjectured that for every graph $H$, there exists $c>0$ such that every $H$-free graph $G$ has a clique or a stable set of size at least $|G|^c$ (a graph is $H$-free if it has no induced subgraph isomorphic to $H$).…

Combinatorics · Mathematics 2026-04-21 Tung Nguyen , Alex Scott , Paul Seymour

Let $H$ be a fixed graph. What can be said about graphs $G$ that have no subgraph isomorphic to a subdivision of $H$? Grohe and Marx proved that such graphs $G$ satisfy a certain structure theorem that is not satisfied by graphs that…

Combinatorics · Mathematics 2022-05-10 Chun-Hung Liu , Robin Thomas

Grohe and Marx proved that if G does not contain H as a topological minor, then there exist constants g=O(|V(H)|^4), D and t depending only on H such that G is a clique sum of graphs that either contain at most t vertices of degree greater…

Combinatorics · Mathematics 2012-09-04 Zdenek Dvorak

A circular-arc hypergraph $H$ is a hypergraph admitting an arc ordering, that is, a circular ordering of the vertex set $V(H)$ such that every hyperedge is an arc of consecutive vertices. An arc ordering is tight if, for any two hyperedges…

Discrete Mathematics · Computer Science 2013-12-05 Johannes Köbler , Sebastian Kuhnert , Oleg Verbitsky

We give new examples and describe the complete lists of all measures on the set of countable homogeneous universal graphs and $K_s$-free homogeneous universal graphs (for $s\geq 3$) that are invariant with respect to the group of all…

Combinatorics · Mathematics 2009-06-30 F. V. Petrov , A. M. Vershik

Let d_i(G) be the density of the 3-vertex i-edge graph in a graph G, i.e., the probability that three random vertices induce a subgraph with i edges. Let S be the set of all quadruples (d_0,d_1,d_2,d_3) that are arbitrary close to 3-vertex…

Combinatorics · Mathematics 2017-04-12 Roman Glebov , Andrzej Grzesik , Ping Hu , Tamas Hubai , Daniel Kral , Jan Volec

Compared to the classical binomial random (hyper)graph model, the study of random regular hypergraphs is made more challenging due to correlations between the occurrence of different edges. We develop an edge-switching technique for…

Combinatorics · Mathematics 2019-07-26 Alberto Espuny Díaz , Felix Joos , Daniela Kühn , Deryk Osthus

The classical global criteria for the existence of Hamilton cycles only apply to graphs with large edge density and small diameter. In a series of papers Asratian and Khachatryan developed local criteria for the existence of Hamilton cycles…

Combinatorics · Mathematics 2021-05-10 Armen S. Asratian , Jonas B. Granholm , Nikolay K. Khachatryan
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