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The Grid Minor Theorem states that for every planar graph $H$, there exists a smallest integer $f(H)$ such that every graph with tree-width at least $f(H)$ contains $H$ as a minor. The only known lower bounds on $f(H)$ beyond the trivial…

Combinatorics · Mathematics 2025-09-15 Chun-Hung Liu , Youngho Yoo

In a reduction sequence of a graph, vertices are successively identified until the graph has one vertex. At each step, when identifying $u$ and $v$, each edge incident to exactly one of $u$ and $v$ is coloured red. Bonnet, Kim, Thomass\'e…

Combinatorics · Mathematics 2025-10-28 Édouard Bonnet , O-joung Kwon , David R. Wood

Twin-width is a newly introduced graph width parameter that aims at generalizing a wide range of "nicely structured" graph classes. In this work, we focus on obtaining good bounds on twin-width $\text{tww}(G)$ for graphs $G$ from a number…

Discrete Mathematics · Computer Science 2022-01-25 Hugo Jacob , Marcin Pilipczuk

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

One of the fundamental results in graph minor theory is that for every planar graph~$H$, there is a minimum integer~$f(H)$ such that graphs with no minor isomorphic to~$H$ have treewidth at most~$f(H)$. The best known bound for an arbitrary…

Combinatorics · Mathematics 2025-01-06 Meike Hatzel , Chun-Hung Liu , Bruce Reed , Sebastian Wiederrecht

We prove that for every fixed integer $s$ and every planar graph $H$, the class of $H$-induced-minor-free and $K_{1,s}$-induced-subgraph-free graphs has polylogarithmic tree-independence number. This is a weakening of a conjecture of…

Combinatorics · Mathematics 2026-01-01 Maria Chudnovsky , Jadwiga Czyżewska , Marcin Pilipczuk , Paweł Rzążewski

In the companion paper [Linear rank-width of distance-hereditary graphs I. A polynomial-time algorithm, Algorithmica 78(1):342--377, 2017], we presented a characterization of the linear rank-width of distance-hereditary graphs, from which…

Combinatorics · Mathematics 2017-08-16 Mamadou Moustapha Kanté , O-joung Kwon

Classes with bounded rankwidth are MSO-transductions of trees and classes with bounded linear rankwidth are MSO-transductions of paths. These results show a strong link between the properties of these graph classes considered from the point…

Logic in Computer Science · Computer Science 2019-11-19 Jaroslav Nesetril , Patrice Ossona de Mendez , Roman Rabinovich , Sebastian Siebertz

For a simple graph $G=(V,E),$ let $\mathcal{S}_+(G)$ denote the set of real positive semidefinite matrices $A=(a_{ij})$ such that $a_{ij}\neq 0$ if $\{i,j\}\in E$ and $a_{ij}=0$ if $\{i,j\}\notin E$. The maximum positive semidefinite…

Combinatorics · Mathematics 2020-05-29 Chassidy Bozeman

A graph $H$ is said to be an induced minor of a graph $G$ if $H$ can be obtained from $G$ by a sequence of vertex deletions and edge contractions. Equivalently, $H$ is an induced minor of $G$ if there exists an induced minor model of $H$ in…

We prove that the (divisorial) gonality of a finite connected graph is lower bounded by its treewidth. We show that equality holds for grid graphs and complete multipartite graphs. We prove that the treewidth lower bound also holds for…

Combinatorics · Mathematics 2022-01-04 Josse van Dobben de Bruyn , Dion Gijswijt

We continue the study of $(\mathrm{tw},\omega)$-bounded graph classes, that is, hereditary graph classes in which the treewidth can only be large due to the presence of a large clique, with the goal of understanding the extent to which this…

Combinatorics · Mathematics 2023-12-19 Clément Dallard , Martin Milanič , Kenny Štorgel

A graph coloring has bounded clustering if each monochromatic component has bounded size. This paper studies such a coloring, where the number of colors depends on an excluded complete bipartite subgraph. This is a much weaker assumption…

Combinatorics · Mathematics 2022-09-29 Chun-Hung Liu , David R. Wood

The celebrated Erd\H{o}s-P\'{o}sa Theorem, in one formulation, asserts that for every $c\geq 1$, graphs with no subgraph (or equivalently, minor) isomorphic to the disjoint union of $c$ cycles have bounded treewidth. What can we say about…

Combinatorics · Mathematics 2025-03-10 Bogdan Alecu , Maria Chudnovsky , Sepehr Hajebi , Sophie Spirkl

It has long been known that the following basic objects are obstructions to bounded tree-width: for arbitrarily large $t$, $(1)$ the complete graph $K_t$, $(2)$ the complete bipartite graph $K_{t,t}$, $(3)$ a subdivision of the $(t \times…

Combinatorics · Mathematics 2024-06-25 Daniel Cocks

We introduce H-clique-width, a new structural measure of graphs that aims to provide a hereditary analogue of the traditional graph product structure. The definition naturally generalises the ordinary clique-width concept. As a result, for…

Combinatorics · Mathematics 2026-05-08 Petr Hliněný , Jan Jedelský

The Planar Graph Product Structure Theorem of Dujmovi\'c et al. [J. ACM '20] says that every planar graph $G$ is contained in $H\boxtimes P\boxtimes K_3$ for some planar graph $H$ with treewidth at most 3 and some path $P$. This result has…

Combinatorics · Mathematics 2025-02-05 Kevin Hendrey , David R. Wood

Many recent works address the question of characterizing induced obstructions to bounded treewidth. In 2022, Lozin and Razgon completely answered this question for graph classes defined by finitely many forbidden induced subgraphs. Their…

For $k \geqslant 0$, we define a simple topological graph $G$ (that is, a graph drawn in the plane such that every pair of edges intersect at most once, including endpoints) to be $k$-matching-planar if for every edge $e \in E(G)$, every…

Combinatorics · Mathematics 2025-10-16 Kevin Hendrey , Nikolai Karol , David R. Wood

We study two notions of being well-structured for classes of graphs that are inspired by classic model theory. A class of graphs $C$ is monadically stable if it is impossible to define arbitrarily long linear orders in vertex-colored graphs…

Discrete Mathematics · Computer Science 2020-07-16 Jaroslav Nesetril , Patrice Ossona de Mendez , Michal Pilipczuk , Roman Rabinovich , Sebastian Siebertz