The Non-Commutative Cycle Lemma
Craig Armstrong, James A. Mingo, Roland Speicher, Jennifer C. H. Wilson
我们提出了一个非交换版本的循环引理Dvoretsky和Motzkin适用于自由群，并使用这个结果来解决一些问题，涉及循环减少在自由群。我们还描述了一个应用程序的随机矩阵，特别是凯斯滕定律的波动。
We present a non-commutative version of the cycle lemma of Dvoretsky and Motzkin that applies to free groups and use this result to solve a number of problems involving cyclic reduction in the free group. We also describe an application to random matrices, in particular the fluctuations of Kesten's Law.
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The bricklayer problem and the Strong Cycle Lemma
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We correct some errors and omissions primarily in a paper [Albertson&Hutchinson2004], discovered by R.B. Richter, and also some in a proof of [Thomassen1993] and of [Yu1997]. We give a short proof of Thomassen's theorem that every triangulation of a surface with all noncontractible cycles sufficiently long can be 5-colored; part of the shortness is due to the use of the Four Color Theorem, which is not used in Thomassen's original proof.
In a recent work, Allen, Böttcher, Hàn, Kohayakawa, and Person provided a first general analogue of the blow-up lemma applicable to sparse (pseudo)random graphs thus generalising the classic tool of Komlós, Sárközy, and Szemerédi. Roughly speaking, they showed that with high probability in the random graph $G_{n,p}$ for $p \geq C(\log n/n)^{1/Δ}$, sparse regular pairs behave similarly as complete bipartite graphs with respect to embedding a spanning graph $H$ with $Δ(H) \leq Δ$. However, this is typically only optimal when $Δ\in \{2,3\}$ and $H$ either contains a triangle ($Δ= 2$) or many copi…
Following the groundbreaking Moser-Tardos algorithm for the Lovasz Local Lemma (LLL), a series of works have exploited a key ingredient of the original analysis, the witness tree lemma, in order to: derive deterministic, parallel and distributed algorithms for the LLL, to estimate the entropy of the output distribution, to partially avoid bad events, to deal with super-polynomially many bad events, and even to devise new algorithmic frameworks. Meanwhile, a parallel line of work, has established tools for analyzing stochastic local search algorithms motivated by the LLL that do not fall within…
For each $k\geq 3$, Green proved an arithmetic $k$-cycle removal lemma for any abelian group $G$. The best known bounds relating the parameters in the lemma for general $G$ are of tower-type. For $k>3$, even in the case $G=\mathbb{F}_2^n$ no better bounds were known prior to this paper. This special case has received considerable attention due to its close connection to property testing of boolean functions. For every $k\geq 3$, we prove a polynomial bound relating the parameters for $G=\mathbb{F}_p^n$, where $p$ is any fixed prime. This extends the result for $k=3$ by the first two authors. D…
In this paper we give a proof of Enomoto's conjecture for graphs of sufficiently large order. Enomoto's conjecture states that, if $G$ is a graph of order $n$ with minimum degree $δ(G)\geq \frac{n}{2}+1$, then for any pair of vertices $x$, $y$ in $G$, there is a Hamiltonian cycle $C$ of $G$ such that $d_C(x,y)=\lfloor \frac{n}{2}\rfloor$. The main tools of our proof are Regularity Lemma of Szemerédi and Blow-up Lemma of Komlós et al.
In this paper, we develop a method for studying cycle lengths in hypergraphs. Our method is built on earlier ones used in [21,22,18]. However, instead of utilizing the well-known lemma of Bondy and Simonovits [4] that most existing methods do, we develop a new and very simple lemma in its place. One useful feature of the new lemma is its adaptiveness for the hypergraph setting. Using this new method, we prove a conjecture of Verstraëte [37] that for $r\ge 3$, every $r$-uniform hypergraph with average degree $Ω(k^{r-1})$ contains Berge cycles of $k$ consecutive lengths. This is sharp up to the …
Sachs and Conway-Gordon used linking number and a beautiful counting argument to prove that every graph in the Petersen family is intrinsically linked (have a pair of disjoint cycles that form a nonsplit link in every spatial embedding) and thus each family member has no flat spatial embedding (an embedding for which every cycle bounds a disk with interior disjoint from the graph). We give an alternate proof that every Petersen family graph has no flat embedding by applying Böhme's Lemma and the Jordan-Brouwer Separation Theorem.
A cycle $C$ of a graph $G$ is \emph{isolating} if every component of $G-V(C)$ is a single vertex. We show that isolating cycles in polyhedral graphs can be extended to larger ones: every isolating cycle $C$ of length $6 \leq |E(C)| < \left \lfloor \frac{2}{3}(|V(G)|+4) \right \rfloor$ implies an isolating cycle $C'$ of larger length that contains $V(C)$. By "hopping" iteratively to such larger cycles, we obtain a powerful and very general inductive motor for proving long cycles and computing them (we will give an algorithm with quadratic running time). This is the first step towards the so far…
We give a new proof of the Skeletal Lemma, which is the main technical tool in our paper on Hamilton cycles in line graphs [T. Kaiser and P. Vrána, Hamilton cycles in 5-connected line graphs, European J. Combin. 33 (2012), 924-947]. It generalises results on disjoint spanning trees in graphs to the context of 3-hypergraphs. The lemma is proved in a slightly stronger version that is more suitable for applications. The proof is simplified and formulated in a more accessible way.
The method of hypergraph containers, introduced recently by Balogh, Morris, and Samotij, and independently by Saxton and Thomason, has proved to be an extremely useful tool in the study of various monotone graph properties. In particular, a fairly straightforward application of this technique allows one to locate, for each non-bipartite graph $H$, the threshold at which the distribution of edges in a typical $H$-free graph with a given number of edges undergoes a transition from 'random-like' to 'structured'. On the other hand, for non-monotone hereditary graph properties the standard version …
Ramsey--Turán Factors of Non-directed Oriented Cycles in Oriented Graphs
该研究针对有向图，证明满足最小半度阈值及独立数条件的足够大的有向图包含指定长度的反有向环因子，其最小半度阈值渐近紧，采用了Ramsey-Turán型格吸收引理完成证明。
The investigation of conditions guaranteeing the appearance of cycles of certain lengths is one of the most well-studied topics in graph theory. In this paper we consider a problem of this type which asks, for fixed integers ${\ell}$ and $k$, how many copies of the $k$-cycle guarantee the appearance of an $\ell$-cycle? Extending previous results of Bollobás--Győri--Li and Alon--Shikhelman, we fully resolve this problem by giving tight (or nearly tight) bounds for all values of $\ell$ and $k$. We also present a somewhat surprising application of the above mentioned estimates to the study of the…
The Non-commutative Topological Vertex and Wall Crossing Phenomena
我们提出了一个推广的拓扑顶点，我们称之为“非交换拓扑顶点”。这给出了没有紧4-圈的复曲面卡-丘流形的开BPS不变量，其中我们有D 0/D2/D 6-膜包裹全纯0/2/6-圈，以及D2-膜包裹圆盘，其边界在D4-膜包裹非紧拉格朗日3-圈上。利用最近提出的晶体熔化模型，组合定义了顶点，并依赖于无穷远处闭弦模的值。一个特殊腔室中的顶点给出了与普通拓扑顶点所计算的相同的答案。证明了复曲面Calabi-Yau流形X的非交换拓扑顶点的恒等式表示为X的轨道折叠的闭BPS配分函数的特殊化，从而给出了顶点的闭表达式.我们还阐明了仿射A_L李代数的Weyl群在Chambers上的作用，并评论了我们的结果对精化BPS不变量的推广。
Element order versus minimal degree in permutation groups: an old lemma with new applications
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The sandpile model on the complete split graph: $q,t$-Schröder polynomials, sawtooth polyominoes, and a cycle lemma
本文研究了完全分裂图上沙堆模型的有序复发配置，通过引入两种塌陷过程和相关统计量，建立了与Schroder路径的联系，并提出了锯齿多米诺的概念。
A graph-theoretic parameter, in a form of a function, called the extra-factorial sum is discussed. The main results are presented in ref. [1] (Nastou et al., Optim Lett, 10, 1203-1220, 2016) and the reader is strongly advised to study the aforementioned paper. The current work presents subject matter in a tutorial form with proofs and some newer unpublished results towards the end (lemma six extension and lemma seven). The extra-factorial sum is relevant to Hamiltonian cycles of complete weighted graphs $WH_n$ with $n$ vertices and is obtained for each edge of $WH_n$. If this sum is multiplied…
In this paper, we study the notion of chordality and cycles in hypergraphs from a commutative algebraic point of view. The corresponding concept of chordality in commutative algebra is having a linear resolution. However, there is no unified definition for cycle or chordality in hypergraphs in the literature, so we consider several generalizations of these notions and study their algebraic interpretations. In particular, we investigate the relationship between chordality and having linear quotients in some classes of hypergraphs. Also we show that if $\mathcal{C}$ is a hypergraph such that $\l…
Hamiltonian cycles in 7-tough $(P_4\cup P_1)$-free graphs
研究7-坚韧无$(P_4\cup P_1)$图的哈密顿圈问题，核心方法是用非对称分离准则和共图覆盖引理取代原框架中的最终割分析，主要贡献是将相关图为哈密顿图的坚韧度界限从23提高到7。
Spread blow-up lemma with an application to perturbed random graphs
本研究结合扩散完美匹配思路与算法化爆破引理，证明扩散版爆破引理，可与Kahn-Kalai猜想互补，并验证了扰动随机图中哈密顿圈幂次阈值猜想的近似版本。
Sharp threshold for Hamilton cycles in randomly perturbed sparse graphs
研究随机扰动稀疏图中哈密顿圈存在的精确概率阈值，通过改进常数至最优值1并证明下界最优性。
Regularity method for hypergraphs with $4$-cycle-free links
该研究将超图正则性方法扩展到顶点链接不含C₄的稀疏3-均匀超图，针对不含K₁,₂,₂且边数为O(|V|^(5/2))的此类超图，建立了七顶点紧圈减一边移除引理的稀疏类似物。
Pósa's Conjecture for graphs of order at least 2\times 10^8
1962年，Pósa证明了n阶最小度至少为2n/3的图G包含一个哈密顿圈的平方。在1996年，范和Kierstead证明了路径版本的Pósa猜想。他们还证明，只要证明G包含长度大于大于2 n/3的圈的平方就足够了。1996年，Komlós、Sárközy和Szemerédi利用正则性和爆破引理证明了Pósa猜想，其中n_0是一个非常大的常数。这里我们不用这些引理证明n_0=2 \times 10 ^8是足够的。我们受到Levitt，Szemerédi和Sárközy最近工作的激励，但我们的方法是基于90年代可用的技术。
For a graph $F$, a hypergraph $\mathcal{H}$ is a Berge copy of $F$ (or a Berge-$F$ in short), if there is a bijection $f : E(F) \rightarrow E(\mathcal{H})$ such that for each $e \in E(F)$ we have $e \subset f(e)$. A hypergraph is Berge-$F$-free if it does not contain a Berge copy of $F$. We denote the maximum number of hyperedges in an $n$-vertex $r$-uniform Berge-$F$-free hypergraph by $\mathrm{ex}_r(n,\textrm{Berge-}F).$ In this paper we prove two general lemmas concerning the maximum size of a Berge-$F$-free hypergraph and use them to establish new results and improve several old results. I…
(Dieudonné and) Dwork's lemma gives a necessary and sufficient condition for an exponential of a formal power series $S(z)$ with coefficients in $Q_p$ to have coefficients in $Z_p$. We establish theorems on the $p$-adic valuation of the coefficients of the exponential of $S(z)$, assuming weaker conditions on the coefficients of $S(z)$ than in Dwork's lemma. As applications, we provide several results concerning lower bounds on the $p$-adic valuation of the number of permutation representations of finitely generated groups. In particular, we give fairly tight lower bounds in the case of an arbi…
Polylogarithmic Bounds for Nested Cycles without Geometric Crossings
该研究解决了Erdős提出的问题，通过多项对数界限证明了在具有足够多边的图中存在k个边不相交且无几何交叉的嵌套循环。
Combining Pósa's rotation lemma with a technique of Kopylov in a novel approach, we prove a generalization of the Erdős-Gallai theorems on cycles and paths. This implies a clique version of the Erdős-Gallai stability theorems and also provides alternative proofs for some recent results.
We present structural results on solutions to the Diophantine system $A{\boldsymbol y} = {\boldsymbol b}$, ${\boldsymbol y} \in \mathbb Z^t_{\ge 0}$ with the smallest number of non-zero entries. Our tools are algebraic and number theoretic in nature and include Siegel's Lemma, generating functions, and commutative algebra. These results have some interesting consequences in discrete optimization.
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