Vertex-minor-closed classes are $χ$-bounded

浅层顶点矿石、稳定性与依赖性

Shallow vertex minors, stability, and dependence

本文研究了浅层顶点矿石在hereditary图类中的稳定性与依赖性，提出稳定和依赖的刻画，并证明了浅层顶点矿石在保持稳定性与依赖性方面的性质。

Linear rank-width of distance-hereditary graphs II. Vertex-minor obstructions

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 we derived an algorithm to compute it in polynomial time. In this paper, we investigate structural properties of distance-hereditary graphs based on this characterization. First, we prove that for a fixed tree $T$, every distance-hereditary graph of sufficiently large linear rank-width contains a vertex-minor isomorphic to $T$. We extend this property to bigg…

Erdös-Pósa property of minor-models with prescribed vertex sets

A minor-model of a graph $H$ in a graph $G$ is a subgraph of $G$ that can be contracted to $H$. We prove that for a positive integer $\ell$ and a non-empty planar graph $H$ with at least $\ell-1$ connected components, there exists a function $f_{H, \ell}:\mathbb{N}\rightarrow \mathbb{R}$ satisfying the property that every graph $G$ with a family of vertex subsets $Z_1, \ldots, Z_m$ contains either $k$ pairwise vertex-disjoint minor-models of $H$ each intersecting at least $\ell$ sets among prescribed vertex sets, or a vertex subset of size at most $f_{H, \ell}(k)$ that meets all such minor-mod…

Unavoidable vertex-minors in large prime graphs

A graph is prime (with respect to the split decomposition) if its vertex set does not admit a partition (A,B) (called a split) with |A|, |B| >= 2 such that the set of edges joining A and B induces a complete bipartite graph. We prove that for each n, there exists N such that every prime graph on at least N vertices contains a vertex-minor isomorphic to either a cycle of length n or a graph consisting of two disjoint cliques of size n joined by a matching.

顶点 minors 的随机图 universality

Vertex-minor universality of a random graph

本文研究了随机图的顶点 minors universality，证明了在特定条件下，随机图可以包含任意子图作为顶点 minors，且验证了相关猜想。

圆图作为顶点子式的 Erdős-Pósa 性质

The Erdős-Pósa property for circle graphs as vertex-minors

本文证明了圆图关于顶点子式具有 Erdős-Pósa 性质，并将相关技术推广到二元拟阵，刻画了含多个指定结构或不含该结构的低秩扰动之间的二分性。

顶点极小Ramsey数：精确值和极值结构

Vertex-minor Ramsey numbers: exact values and extremal structure

本文确定了顶点极小Ramsey数Rvm(4)=11，并通过局部补运算对10和11顶点的图进行穷举分类，揭示了极值结构及方法。

Dense minors of graphs with independence number two

Motivated by Hadwiger's conjecture, we prove that every $n$-vertex graph $G$ with no independent set of size three contains an $\lceil n/2\rceil$-vertex simple minor $H$ with $$0.98688 \cdot \binom{|V(H)|}{2} - o(n^2)$$ edges.

Extremal $K_4$-minor-free graphs without short cycles

We determine the maximum number of edges in a $K_4$-minor-free $n$-vertex graph of girth $g$, when $g = 5$ or $g$ is even. We argue that there are many different $n$-vertex extremal graphs, if $n$ is even and $g$ is odd.

The complexity of the vertex-minor problem

A graph H is a vertex-minor of a graph G if it can be reached from G by the successive application of local complementations and vertex deletions. Vertex-minors have been the subject of intense study in graph theory over the last decades and have found applications in other fields such as quantum information theory. Therefore it is natural to consider the computational complexity of deciding whether a given graph G has a vertex-minor isomorphic to another graph H, which was previously unknown. Here we prove that this decision problem is NP-complete, even when restricting H, G to be circle grap…

Tree-depth and Vertex-minors

In a recent paper, Kwon and Oum claim that every graph of bounded rank-width is a pivot-minor of a graph of bounded tree-width (while the converse has been known true already before). We study the analogous questions for "depth" parameters of graphs, namely for the tree-depth and related new shrub-depth. We show that shrub-depth is monotone under taking vertex-minors, and that every graph class of bounded shrub-depth can be obtained via vertex-minors of graphs of bounded tree-depth. We also consider the same questions for bipartite graphs and pivot-minors.

禁止子图或矿脉中的细分爪

Forbidding the subdivided claw as a subgraph or a minor

本文研究了禁止细分爪作为子图或矿脉的图的性质，并探讨了其在Turán数、路径宽度和图增长常数中的应用。

秩宽至多为二的图的排除顶点子式和枢轴子式

The Excluded Vertex-Minors and Pivot-Minors for Rank-Width at Most Two

该研究确定秩宽至多为二的图类的排除顶点子式和排除枢轴子式，通过反转素图单顶点约化定理，利用规范键确定等价类，借助计算机辅助计算得出具体数量，完善了相关列表。

Extremal density for sparse minors and subdivisions

We prove an asymptotically tight bound on the extremal density guaranteeing subdivisions of bounded-degree bipartite graphs with a mild separability condition. As corollaries, we answer several questions of Reed and Wood on embedding sparse minors. Among others, $\bullet$ $(1+o(1))t^2$ average degree is sufficient to force the $t\times t$ grid as a topological minor; $\bullet$ $(3/2+o(1))t$ average degree forces every $t$-vertex planar graph as a minor, and the constant $3/2$ is optimal, furthermore, surprisingly, the value is the same for $t$-vertex graphs embeddable on any fixed surface; $\b…

Complete Graph Minors and the Graph Minor Structure Theorem

The graph minor structure theorem by Robertson and Seymour shows that every graph that excludes a fixed minor can be constructed by a combination of four ingredients: graphs embedded in a surface of bounded genus, a bounded number of vortices of bounded width, a bounded number of apex vertices, and the clique-sum operation. This paper studies the converse question: What is the maximum order of a complete graph minor in a graph constructed using these four ingredients? Our main result answers this question up to a constant factor.

Cliques in Graphs Excluding a Complete Graph Minor

This paper considers the following question: What is the maximum number of $k$-cliques in an $n$-vertex graph with no $K_t$-minor? This question generalises the extremal function for $K_t$-minors, which corresponds to the $k=2$ case. The exact answer is given for $t\leq 9$ and all values of $k$. We also determine the maximum total number of cliques in an $n$-vertex graph with no $K_t$-minor for $t\leq 9$. Several observations are made about the case of general $t$.

几乎所有图都是顶点-矿石通用的

Almost all graphs are vertex-minor universal

该研究证明了随机图在顶点-矿石通用性上的性质，并引入了顶点-矿石Ramsey数，探讨了其多项式下界。

Rooted prism-minors and disjoint cycles containing a specified edge

Dirac and Lovász independently characterized the $3$-connected graphs with no pair of vertex-disjoint cycles. Equivalently, they characterized all $3$-connected graphs with no prism-minors. In this paper, we completely characterize the $3$-connected graphs with an edge that is contained in the union of no pair of vertex-disjoint cycles. As applications, we answer the analogous questions for edge-disjoint cycles and for $4$-connected graphs and we completely characterize the $3$-connected graphs with no prism-minor using a specified edge.

Excluded minors in cubic graphs

Let G be a cubic graph, with girth at least five, such that for every partition X,Y of its vertex set with |X|,|Y|>6 there are at least six edges between X and Y. We prove that if there is no homeomorphic embedding of the Petersen graph in G, and G is not one particular 20-vertex graph, then either G\v is planar for some vertex v, or G can be drawn with crossings in the plane, but with only two crossings, both on the infinite region. We also prove several other theorems of the same kind.

Improper coloring of graphs with no odd clique minor

As a strengthening of Hadwiger's conjecture, Gerards and Seymour conjectured that every graph with no odd $K_t$ minor is $(t-1)$-colorable. We prove two weaker variants of this conjecture. Firstly, we show that for each $t \geq 2$, every graph with no odd $K_t$ minor has a partition of its vertex set into $6t-9$ sets $V_1, \dots, V_{6t-9}$ such that each $V_i$ induces a subgraph of bounded maximum degree. Secondly, we prove that for each $t \geq 2$, every graph with no odd $K_t$ minor has a partition of its vertex set into $10t-13$ sets $V_1, \dots, V_{10t-13}$ such that each $V_i$ induces a s…

无F- minors图的谱半径

The spectral radius of minor free graphs

本文针对由完全图删除不相交路径得到的F，给出了足够大n时不含F- minors的n顶点图谱半径的尖锐上界，并刻画了极图，扩展了边数结论。

素图的素顶点子式

Prime vertex-minors of a prime graph

本文研究素图中非本质顶点的存在数量，将 Allys 的结果从至少一个加强到至少两个，并进一步证明在排除特定局部等价类后至少有三个非本质顶点，同时给出关于 pivot-minor 的类似结论。

4连通图无6轮子 minors 的特征刻画

A characterization of 4-connected graphs with no 6-wheel minor

本文研究4连通图中不含6轮子minor的图结构，通过分析确定所有符合条件的图类。

Minors, connectivity, and diameter in randomly perturbed sparse graphs

Extremal properties of sparse graphs, randomly perturbed by the binomial random graph are considered. It is known that every $n$-vertex graph $G$ contains a complete minor of order $Ω(n/α(G))$. We prove that adding $ξn$ random edges, where $ξ> 0$ is arbitrarily small yet fixed, to an $n$-vertex graph $G$ satisfying $α(G) \leq ζ(ξ)n$ asymptotically almost surely results in a graph containing a complete minor of order $\tilde Ω\left( n/\sqrt{α(G)}\right)$; this result is tight up to the implicit logarithmic terms. For complete topological minors, we prove that there exists a constant $C>0$ such …

Islands in minor-closed classes. I. Bounded treewidth and separators

The clustered chromatic number of a graph class is the minimum integer $t$ such that for some $C$ the vertices of every graph in the class can be colored in $t$ colors so that every monochromatic component has size at most $C$. We show that the clustered chromatic number of the class of graphs embeddable on a given surface is four, proving the conjecture of Esperet and Ochem. Additionally, we study the list version of the concept and characterize the minor-closed classes of graphs of bounded treewidth with given clustered list chromatic number. We further strengthen the above results to solve …

具有排除子式的图的弱直径可选性

Weak diameter choosability of graphs with an excluded minor

本文扩展了Dvořák和Norin的结果，证明了对于任意图H，H-无子式图具有有界弱直径的最优3-可选性，并在H为平面图时证明了更强的预着色扩展结果及指数级着色存在性，同时指出该列表着色结果无法扩展至奇无子式图。

圆稳定子态与禁止任意顶点子式态中的渐近纠缠

Asymptotic entanglement in circle stabilizer states and states forbidding arbitrary vertex-minors

本文基于Geelen的顶点子式弱结构猜想，建立稳定子态渐近纠缠与禁止顶点子式的关联，证明不包含固定稳定子态为顶点子式的稳定子态的纠缠受渐近约束，为量子器件纠缠研究提供支撑。

6轮图的排除极小定理

An excluded minor theorem for the 6-wheel

本文研究6轮图的极小图特性，通过分析平面图与非平面图的结构，完成对不含6轮图作为子图的图的完整分类。

Nonrepetitive colourings of graphs excluding a fixed immersion or topological minor

We prove that graphs excluding a fixed immersion have bounded nonrepetitive chromatic number. More generally, we prove that if $H$ is a fixed planar graph that has a planar embedding with all the vertices with degree at least 4 on a single face, then graphs excluding $H$ as a topological minor have bounded nonrepetitive chromatic number. This is the largest class of graphs known to have bounded nonrepetitive chromatic number.

Minors for alternating dimaps

We develop a theory of minors for alternating dimaps --- orientably embedded digraphs where, at each vertex, the incident edges (taken in the order given by the embedding) are directed alternately into, and out of, the vertex. We show that they are related by the triality relation of Tutte. They do not commute in general, though do in many circumstances, and we characterise the situations where they do. The relationship with triality is reminiscent of similar relationships for binary functions, due to the author, so we characterise those alternating dimaps which correspond to binary functions.…

树宽与团数：诱导子式

Treewidth versus clique number: induced minors

本文证明遗传图类的树宽-团数有界性等价于其诱导子式类的树宽-团数有界性。

Robertson猜想 I. 通过拓扑次式关系对有界树宽图的良拟序

Robertson's conjecture I. Well-quasi-ordering bounded tree-width graphs by the topological minor relation

本文证明了有界树宽图的Robertson猜想，即不包含特定拓扑次式的图按拓扑次式关系构成良拟序，这是迈向完整证明的关键步骤，且证明自包含并蕴含已知结果。

扇图膨胀中的真次闭类

Proper Minor-Closed Classes in Blowups of Fans

本文肯定回答了 Dujmović 等人的问题，证明任意 $n$ 顶点 $K_t$-次免图均包含于扇图的 $O_t(\sqrt{n}\log^2(n))$-膨胀中。

On Andreae's Ubiquity Conjecture

A graph $H$ is ubiquitous if for every graph $G$ that for every natural number $n$ contains $n$ vertex-disjoint $H$-minors contains infinitely many vertex-disjoint $H$-minors. Andreae conjectured that every locally finite graph is ubiquitous. We give a disconnected counterexample to this conjecture. It remains open whether every connected locally finite graph is ubiquitous.

排除子图和子式的图的聚类着色

Clustered Coloring of Graphs Excluding a Subgraph and a Minor

本文研究排除子图和/或子式的图的聚类着色问题，证明了多类图的有界聚类着色数最优界，改进了奇子式相关猜想的现有界值。

Topological minors of cover graphs and dimension

We show that posets of bounded height whose cover graphs exclude a fixed graph as a topological minor have bounded dimension. This result was already proven by Walczak. However, our argument is entirely combinatorial and does not rely on structural decomposition theorems. Given a poset with large dimension but bounded height, we directly find a large clique subdivision in its cover graph. Therefore, our proof is accessible to readers not familiar with topological graph theory, and it allows us to provide explicit upper bounds on the dimension. With the introduced tools we show a second result …

Classes of graphs with no long cycle as a vertex-minor are polynomially $χ$-bounded

A class $\mathcal G$ of graphs is $χ$-bounded if there is a function $f$ such that for every graph $G\in \mathcal G$ and every induced subgraph $H$ of $G$, $χ(H)\le f(ω(H))$. In addition, we say that $\mathcal G$ is polynomially $χ$-bounded if $f$ can be taken as a polynomial function. We prove that for every integer $n\ge3$, there exists a polynomial $f$ such that $χ(G)\le f(ω(G))$ for all graphs with no vertex-minor isomorphic to the cycle graph $C_n$. To prove this, we show that if $\mathcal G$ is polynomially $χ$-bounded, then so is the closure of $\mathcal G$ under taking the $1$-join ope…

Clustered colouring of graph classes with bounded treedepth or pathwidth

The "clustered chromatic number" of a class of graphs is the minimum integer $k$ such that for some integer $c$ every graph in the class is $k$-colourable with monochromatic components of size at most $c$. We determine the clustered chromatic number of any minor-closed class with bounded treedepth, and prove a best possible upper bound on the clustered chromatic number of any minor-closed class with bounded pathwidth. As a consequence, we determine the fractional clustered chromatic number of every minor-closed class.

Planar Decompositions and the Crossing Number of Graphs with an Excluded Minor

Tree decompositions of graphs are of fundamental importance in structural and algorithmic graph theory. Planar decompositions generalise tree decompositions by allowing an arbitrary planar graph to index the decomposition. We prove that every graph that excludes a fixed graph as a minor has a planar decomposition with bounded width and a linear number of bags. The crossing number of a graph is the minimum number of crossings in a drawing of the graph in the plane. We prove that planar decompositions are intimately related to the crossing number. In particular, a graph with bounded degree has l…

Spectral extrema of $K_{s,t}$-minor free graphs--On a conjecture of M. Tait

Minors play an important role in extremal graph theory and spectral extremal graph theory. Tait [The Colin de Verdière parameter, excluded minors, and the spectral radius, J. Combin. Theory Ser. A 166 (2019) 42--58] determined the maximum spectral radius and characterized the unique extremal graph for $K_r$-minor free graphs of sufficiently large order $n$, he also made great progress on $K_{s,t}$-minor free graphs and posed a conjecture: Let $2\leq s\leq t$ and $n-s+1=pt+q$, where $n$ is sufficiently large and $1\leq q\leq t.$ Then $K_{s-1}\nabla (pK_t\cup K_q)$ is the unique extremal graph w…

Graphs without large $K_{2,n}$-minors

The purpose of this paper is to characterize graphs that do not have a large $K_{2,n}$-minor. As corollaries, it is proved that, for any given positive integer $n$, every sufficiently large 3-connected graph with minimum degree at least six, every 4-connected graph with a vertex of sufficiently high degree, and every sufficiently large 5-connected graph must have a $K_{2,n}$-minor.

Excluded vertex-minors for graphs of linear rank-width at most k

Linear rank-width is a graph width parameter, which is a variation of rank-width by restricting its tree to a caterpillar. As a corollary of known theorems, for each $k$, there is a finite obstruction set $\mathcal{O}_k$ of graphs such that a graph $G$ has linear rank-width at most $k$ if and only if no vertex-minor of $G$ is isomorphic to a graph in $\mathcal{O}_k$. However, no attempts have been made to bound the number of graphs in $\mathcal{O}_k$ for $k\ge 2$. We show that for each $k$, there are at least $2^{Ω(3^k)}$ pairwise locally non-equivalent graphs in $\mathcal{O}_k$, and therefore…

A short derivation of the structure theorem for graphs with excluded topological minors

As a major step in their proof of Wagner's conjecture, Robertson and Seymour showed that every graph not containing a fixed graph $H$ as a minor has a tree-decomposition in which each torso is almost embeddable in a surface of bounded genus. Recently, Grohe and Marx proved a similar result for graphs not containing $H$ as a topological minor. They showed that every graph which does not contain $H$ as a topological minor has a tree-decomposition in which every torso is either almost embeddable in a surface of bounded genus, or has a bounded number of vertices of high degree. We give a short pro…

The extremal function for Petersen minors

We prove that every graph with $n$ vertices and at least $5n-8$ edges contains the Petersen graph as a minor, and this bound is best possible. Moreover we characterise all Petersen-minor-free graphs with at least $5n-11$ edges. It follows that every graph containing no Petersen minor is 9-colourable and has vertex arboricity at most 5. These results are also best possible.

Rank-width and Tree-width of H-minor-free Graphs

We prove that for any fixed r>=2, the tree-width of graphs not containing K_r as a topological minor (resp. as a subgraph) is bounded by a linear (resp. polynomial) function of their rank-width. We also present refinements of our bounds for other graph classes such as K_r-minor free graphs and graphs of bounded genus.

A note on "Extremal graphs with bounded vertex bipartiteness number"

This paper is devoted to present two counterexamples to the theorem from \cite{MK} Maria R., Katherine T. M., Bernardo S. M., Extremal graphs with bounded vertex bipartiteness number, Linear Algebra Appl. 493 (2016) 28-36. Moreover, the corrected theorem and proof are presented.

Minor-closed graph classes with bounded layered pathwidth

We prove that a minor-closed class of graphs has bounded layered pathwidth if and only if some apex-forest is not in the class. This generalises a theorem of Robertson and Seymour, which says that a minor-closed class of graphs has bounded pathwidth if and only if some forest is not in the class.

Spectral extremal graphs without intersecting triangles as a minor

Let $F_s$ be the friendship graph obtained from $s$ triangles by sharing a common vertex. For fixed $s\ge 2$ and sufficiently large $n$, the $F_s$-free graphs of order $n$ which attain the maximal spectral radius was firstly characterized by Cioabă, Feng, Tait and Zhang [Electron. J. Combin. 27 (4) (2020)],and later uniquely determined by Zhai, Liu and Xue [Electron. J. Combin. 29 (3) (2022)]. Recently, the spectral extremal problems was widely studied for graphs containing no $H$ as a minor. For instance, Tait [J. Combin. Theory Ser. A 166 (2019)], Zhai and Lin [J. Combin. Theory Ser. B 157 (…

二元 matroid 与有限度的 pivot-minor

Binary matroids and degree-boundedness for pivot-minors

本文基于二元 matroid 结构定理，证明了排除 H 作为 pivot-minor 的 K_{s,s}-free 图类具有有界平均度，并展示了 K_{s,t}-free 双色圈图中存在度数受限的顶点。

Random graphs from a weighted minor-closed class

There has been much recent interest in random graphs sampled uniformly from the n-vertex graphs in a suitable minor-closed class, such as the class of all planar graphs. Here we use combinatorial and probabilistic methods to investigate a more general model. We consider random graphs from a `well-behaved' class of graphs: examples of such classes include all minor-closed classes of graphs with 2-connected excluded minors (such as forests, series-parallel graphs and planar graphs), the class of graphs embeddable on any given surface, and the class of graphs with at most k vertex-disjoint cycles…

Extremal results regarding $K_6$-minors in graphs of girth at least 5

We prove that every 6-connected graph of girth $\geq 6$ has a $K_6$-minor and thus settle the Jorgensen conjecture for graphs of girth $ \geq 6$. Relaxing the assumption on the girth, we prove that every 6-connected $n$-vertex graph of size $\geq 3 1/5 n-8$ and of girth $\geq 5$ contains a $K_6$-minor.

利用平均度寻找稠密子式

Finding dense minors using average degree

受哈德维格猜想启发，研究平均度至少为$t-1$的图中最稠密$t$顶点子式的边数下界，给出渐近最优结果及$t\leq 6$时的精确值。

Characterisations and Examples of Graph Classes with Bounded Expansion

Classes with bounded expansion, which generalise classes that exclude a topological minor, have recently been introduced by Nešetřil and Ossona de Mendez. These classes are defined by the fact that the maximum average degree of a shallow minor of a graph in the class is bounded by a function of the depth of the shallow minor. Several linear-time algorithms are known for bounded expansion classes (such as subgraph isomorphism testing), and they allow restricted homomorphism dualities, amongst other desirable properties. In this paper we establish two new characterisations of bounded expansion c…

Properties of $8$-contraction-critical graphs with no $K_7$ minor

Motivated by the famous Hadwiger's Conjecture, we study the properties of $8$-contraction-critical graphs with no $K_7$ minor; we prove that every $8$-contraction-critical graph with no $K_7$ minor has at most one vertex of degree $8$, where a graph $G$ is $8$-contraction-critical if $G$ is not $7$-colorable but every proper minor of $G$ is $7$-colorable. This is one step in our effort to prove that every graph with no $K_7$ minor is $7$-colorable, which remains open.