European Journal of Combinatorics最新文献

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Stability properties for subgroups generated by return words 由返回字生成的子组的稳定性
IF 1 3区 数学
European Journal of Combinatorics Pub Date : 2025-07-26 DOI: 10.1016/j.ejc.2025.104224
France Gheeraert , Herman Goulet-Ouellet , Julien Leroy , Pierre Stas
{"title":"Stability properties for subgroups generated by return words","authors":"France Gheeraert ,&nbsp;Herman Goulet-Ouellet ,&nbsp;Julien Leroy ,&nbsp;Pierre Stas","doi":"10.1016/j.ejc.2025.104224","DOIUrl":"10.1016/j.ejc.2025.104224","url":null,"abstract":"<div><div>Return words are a classical tool for studying shift spaces with low factor complexity. In recent years, their projection inside groups have attracted some attention, for instance in the context of dendric shift spaces, of generation of pseudorandom numbers (through the welldoc property), and of profinite invariants of shift spaces. Aiming at unifying disparate works, we introduce a notion of stability for subgroups generated by return words. Within this framework, we revisit several existing results and generalize some of them. We also study general aspects of stability, such as decidability or closure under certain operations.</div></div>","PeriodicalId":50490,"journal":{"name":"European Journal of Combinatorics","volume":"130 ","pages":"Article 104224"},"PeriodicalIF":1.0,"publicationDate":"2025-07-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144711391","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Decomposing random regular graphs into stars 将随机规则图分解成星形
IF 1 3区 数学
European Journal of Combinatorics Pub Date : 2025-07-16 DOI: 10.1016/j.ejc.2025.104216
Michelle Delcourt , Catherine Greenhill , Mikhail Isaev , Bernard Lidický , Luke Postle
{"title":"Decomposing random regular graphs into stars","authors":"Michelle Delcourt ,&nbsp;Catherine Greenhill ,&nbsp;Mikhail Isaev ,&nbsp;Bernard Lidický ,&nbsp;Luke Postle","doi":"10.1016/j.ejc.2025.104216","DOIUrl":"10.1016/j.ejc.2025.104216","url":null,"abstract":"<div><div>We study <span><math><mi>k</mi></math></span>-star decompositions, that is, partitions of the edge set into disjoint stars with <span><math><mi>k</mi></math></span> edges, in the uniformly random <span><math><mi>d</mi></math></span>-regular graph model <span><math><msub><mrow><mi>G</mi></mrow><mrow><mi>n</mi><mo>,</mo><mi>d</mi></mrow></msub></math></span>. Using the small subgraph conditioning method, we prove an existence result for such decompositions for all <span><math><mrow><mi>d</mi><mo>,</mo><mi>k</mi></mrow></math></span> such that <span><math><mrow><mi>d</mi><mo>/</mo><mn>2</mn><mo>&lt;</mo><mi>k</mi><mo>≤</mo><mi>d</mi><mo>/</mo><mn>2</mn><mo>+</mo><mo>max</mo><mrow><mo>{</mo><mn>1</mn><mo>,</mo><mfrac><mrow><mn>1</mn></mrow><mrow><mn>6</mn></mrow></mfrac><mo>log</mo><mi>d</mi><mo>}</mo></mrow></mrow></math></span>. More generally, we give a sufficient existence condition that can be checked numerically for any given values of <span><math><mi>d</mi></math></span> and <span><math><mi>k</mi></math></span>. Complementary negative results are obtained using the independence ratio of random regular graphs. Our results establish an existence threshold for <span><math><mi>k</mi></math></span>-star decompositions in <span><math><msub><mrow><mi>G</mi></mrow><mrow><mi>n</mi><mo>,</mo><mi>d</mi></mrow></msub></math></span> for all <span><math><mrow><mi>d</mi><mo>≤</mo><mn>100</mn></mrow></math></span> and <span><math><mrow><mi>k</mi><mo>&gt;</mo><mi>d</mi><mo>/</mo><mn>2</mn></mrow></math></span>.</div><div>For smaller values of <span><math><mi>k</mi></math></span>, the connection between <span><math><mi>k</mi></math></span>-star decompositions and <span><math><mi>β</mi></math></span>-orientations allows us to apply results of Thomassen (2012) and Lovász et al. (2013). We prove that random <span><math><mi>d</mi></math></span>-regular graphs satisfy their assumptions with high probability, thus establishing a.a.s. existence of <span><math><mi>k</mi></math></span>-star decompositions (i) when <span><math><mrow><mn>2</mn><msup><mrow><mi>k</mi></mrow><mrow><mn>2</mn></mrow></msup><mo>+</mo><mi>k</mi><mo>≤</mo><mi>d</mi></mrow></math></span>, and (ii) when <span><math><mi>k</mi></math></span> is odd and <span><math><mrow><mi>k</mi><mo>&lt;</mo><mi>d</mi><mo>/</mo><mn>2</mn></mrow></math></span>.</div></div>","PeriodicalId":50490,"journal":{"name":"European Journal of Combinatorics","volume":"130 ","pages":"Article 104216"},"PeriodicalIF":1.0,"publicationDate":"2025-07-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144634400","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Generalized diagonals in positive semi-definite matrices 正半定矩阵中的广义对角线
IF 1 3区 数学
European Journal of Combinatorics Pub Date : 2025-07-12 DOI: 10.1016/j.ejc.2025.104220
Robert Angarone , Daniel Soskin
{"title":"Generalized diagonals in positive semi-definite matrices","authors":"Robert Angarone ,&nbsp;Daniel Soskin","doi":"10.1016/j.ejc.2025.104220","DOIUrl":"10.1016/j.ejc.2025.104220","url":null,"abstract":"<div><div>We describe all inequalities among generalized diagonals in positive semi-definite matrices. These turn out to be governed by a simple partial order on the symmetric group. This provides an analogue of results of Drake, Gerrish, and Skandera on inequalities among generalized diagonals in totally nonnegative matrices.</div></div>","PeriodicalId":50490,"journal":{"name":"European Journal of Combinatorics","volume":"130 ","pages":"Article 104220"},"PeriodicalIF":1.0,"publicationDate":"2025-07-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144611621","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Borsuk and Vázsonyi problems through Reuleaux polyhedra Borsuk和Vázsonyi问题通过勒洛多面体
IF 1 3区 数学
European Journal of Combinatorics Pub Date : 2025-07-12 DOI: 10.1016/j.ejc.2025.104215
Gyivan Lopez-Campos , Déborah Oliveros , Jorge L. Ramírez Alfonsín
{"title":"Borsuk and Vázsonyi problems through Reuleaux polyhedra","authors":"Gyivan Lopez-Campos ,&nbsp;Déborah Oliveros ,&nbsp;Jorge L. Ramírez Alfonsín","doi":"10.1016/j.ejc.2025.104215","DOIUrl":"10.1016/j.ejc.2025.104215","url":null,"abstract":"<div><div>The Borsuk conjecture and the Vázsonyi problem are two attractive and famous questions in discrete and combinatorial geometry, both based on the notion of diameter of bounded sets. In this paper, we present an equivalence between the critical sets with Borsuk number 4 in <span><math><msup><mrow><mi>R</mi></mrow><mrow><mn>3</mn></mrow></msup></math></span> and the minimal structures for the Vázsonyi problem by using the well-known Reuleaux polyhedra. The latter leads to a full characterization of all finite sets in <span><math><msup><mrow><mi>R</mi></mrow><mrow><mn>3</mn></mrow></msup></math></span> with Borsuk number 4.</div><div>The proof of such equivalence needs various ingredients, in particular, we proved a conjecture dealing with <em>strongly critical configuration</em> for the Vázsonyi problem and showed that the diameter graph arising from involutive polyhedra is vertex (and edge) 4-critical.</div></div>","PeriodicalId":50490,"journal":{"name":"European Journal of Combinatorics","volume":"130 ","pages":"Article 104215"},"PeriodicalIF":1.0,"publicationDate":"2025-07-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144605223","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Faces in rectilinear drawings of complete graphs 完全图的直线图中的面
IF 1 3区 数学
European Journal of Combinatorics Pub Date : 2025-07-11 DOI: 10.1016/j.ejc.2025.104217
Martin Balko , Anna Brötzner , Fabian Klute , Josef Tkadlec
{"title":"Faces in rectilinear drawings of complete graphs","authors":"Martin Balko ,&nbsp;Anna Brötzner ,&nbsp;Fabian Klute ,&nbsp;Josef Tkadlec","doi":"10.1016/j.ejc.2025.104217","DOIUrl":"10.1016/j.ejc.2025.104217","url":null,"abstract":"<div><div>We initiate the study of extremal problems about faces in <em>convex rectilinear drawings</em> of <span><math><msub><mrow><mi>K</mi></mrow><mrow><mi>n</mi></mrow></msub></math></span>, that is, drawings where vertices are represented by points in the plane in convex position and edges by line segments between the points representing the end-vertices. We show that if a convex rectilinear drawing of <span><math><msub><mrow><mi>K</mi></mrow><mrow><mi>n</mi></mrow></msub></math></span> does not contain a common interior point of at least three edges, then there is always a face forming a convex 5-gon while there are such drawings without any face forming a convex <span><math><mi>k</mi></math></span>-gon with <span><math><mrow><mi>k</mi><mo>≥</mo><mn>6</mn></mrow></math></span>.</div><div>A convex rectilinear drawing of <span><math><msub><mrow><mi>K</mi></mrow><mrow><mi>n</mi></mrow></msub></math></span> is <em>regular</em> if its vertices correspond to vertices of a regular convex <span><math><mi>n</mi></math></span>-gon. We characterize positive integers <span><math><mi>n</mi></math></span> for which regular drawings of <span><math><msub><mrow><mi>K</mi></mrow><mrow><mi>n</mi></mrow></msub></math></span> contain a face forming a convex 5-gon.</div><div>To our knowledge, this type of problems has not been considered in the literature before and so we also pose several new natural open problems.</div></div>","PeriodicalId":50490,"journal":{"name":"European Journal of Combinatorics","volume":"130 ","pages":"Article 104217"},"PeriodicalIF":1.0,"publicationDate":"2025-07-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144596135","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
A decomposition of cylindric partitions and cylindric partitions into distinct parts 将圆柱分区和圆柱分区分解成不同的部分
IF 1 3区 数学
European Journal of Combinatorics Pub Date : 2025-07-11 DOI: 10.1016/j.ejc.2025.104219
Kağan Kurşungöz, Halı̇me Ömrüuzun Seyrek
{"title":"A decomposition of cylindric partitions and cylindric partitions into distinct parts","authors":"Kağan Kurşungöz,&nbsp;Halı̇me Ömrüuzun Seyrek","doi":"10.1016/j.ejc.2025.104219","DOIUrl":"10.1016/j.ejc.2025.104219","url":null,"abstract":"<div><div>We introduce the notion of <em>pivot</em> in a chain of skew diagrams in the context of cylindric partitions. Then, we show that cylindric partitions are in one-to-one correspondence with a pair consisting of an ordinary partition and a suitably restricted chain of pivots. Next, we show the general form of the generating function for cylindric partitions into distinct parts and give some examples. We prove part of a conjecture by Corteel, Dousse, and Uncu. The approaches and proofs are elementary and combinatorial.</div></div>","PeriodicalId":50490,"journal":{"name":"European Journal of Combinatorics","volume":"130 ","pages":"Article 104219"},"PeriodicalIF":1.0,"publicationDate":"2025-07-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144605306","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Proof of a conjecture on the shape-Wilf-equivalence for partially ordered patterns 部分有序模式的形状-威尔夫等价的一个猜想的证明
IF 1 3区 数学
European Journal of Combinatorics Pub Date : 2025-07-09 DOI: 10.1016/j.ejc.2025.104222
Lintong Wang, Sherry H.F. Yan
{"title":"Proof of a conjecture on the shape-Wilf-equivalence for partially ordered patterns","authors":"Lintong Wang,&nbsp;Sherry H.F. Yan","doi":"10.1016/j.ejc.2025.104222","DOIUrl":"10.1016/j.ejc.2025.104222","url":null,"abstract":"<div><div>A partially ordered pattern (abbreviated POP) is a partially ordered set (poset) that generalizes the notion of a pattern when we are not concerned with the relative order of some of its letters. The notion of partially ordered patterns provides a convenient language to deal with large sets of permutation patterns. In analogy to the shape-Wilf-equivalence for permutation patterns, Burstein–Han–Kitaev–Zhang initiated the study of the shape-Wilf-equivalence for POPs which would result in the shape-Wilf-equivalence for large sets of permutation patterns. The main objective of this paper is to confirm a recent intriguing conjecture posed by Burstein–Han–Kitaev–Zhang concerning the shape-Wilf-equivalence for POPs of length <span><math><mi>k</mi></math></span>. This is accomplished by establishing a bijection between two sets of pattern-avoiding transversals of a given Young diagram.</div></div>","PeriodicalId":50490,"journal":{"name":"European Journal of Combinatorics","volume":"130 ","pages":"Article 104222"},"PeriodicalIF":1.0,"publicationDate":"2025-07-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144579676","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Partial-dual genus polynomial of graphs 图的偏对偶格多项式
IF 1 3区 数学
European Journal of Combinatorics Pub Date : 2025-07-09 DOI: 10.1016/j.ejc.2025.104221
Zhiyun Cheng
{"title":"Partial-dual genus polynomial of graphs","authors":"Zhiyun Cheng","doi":"10.1016/j.ejc.2025.104221","DOIUrl":"10.1016/j.ejc.2025.104221","url":null,"abstract":"<div><div>Recently, Chmutov introduced the partial duality of ribbon graphs, which can be regarded as a generalization of the classical Euler-Poincaré duality. The partial-dual genus polynomial <span><math><mrow><msup><mrow></mrow><mrow><mi>∂</mi></mrow></msup><msub><mrow><mi>ɛ</mi></mrow><mrow><mi>G</mi></mrow></msub><mrow><mo>(</mo><mi>z</mi><mo>)</mo></mrow></mrow></math></span> is an enumeration of the partial duals of <span><math><mi>G</mi></math></span> by Euler genus. For an intersection graph derived from a given chord diagram, the partial-dual genus polynomial can be defined by considering the ribbon graph associated to the chord diagram. In this paper, we provide a combinatorial approach to the partial-dual genus polynomial in terms of intersection graphs without referring to chord diagrams. After extending the definition of the partial-dual genus polynomial from intersection graphs to all graphs, we prove that it satisfies the four-term relation of graphs. This provides an answer to a problem proposed by Chmutov (2023).</div></div>","PeriodicalId":50490,"journal":{"name":"European Journal of Combinatorics","volume":"130 ","pages":"Article 104221"},"PeriodicalIF":1.0,"publicationDate":"2025-07-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144579677","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Quasisymmetric Schur Q-functions and peak Young quasisymmetric Schur functions 准对称舒尔q函数和峰值杨准对称舒尔函数
IF 1 3区 数学
European Journal of Combinatorics Pub Date : 2025-07-08 DOI: 10.1016/j.ejc.2025.104213
Seung-Il Choi , Sun-Young Nam , Young-Tak Oh
{"title":"Quasisymmetric Schur Q-functions and peak Young quasisymmetric Schur functions","authors":"Seung-Il Choi ,&nbsp;Sun-Young Nam ,&nbsp;Young-Tak Oh","doi":"10.1016/j.ejc.2025.104213","DOIUrl":"10.1016/j.ejc.2025.104213","url":null,"abstract":"<div><div>In this paper, we explore the relationship between quasisymmetric Schur <span><math><mi>Q</mi></math></span>-functions and peak Young quasisymmetric Schur functions. We introduce a bijection on <span><math><mrow><mi>SPIT</mi><mrow><mo>(</mo><mi>α</mi><mo>)</mo></mrow></mrow></math></span> such that <span><math><mrow><mo>{</mo><msub><mrow><mi>w</mi></mrow><mrow><mi>c</mi></mrow></msub><mrow><mo>(</mo><mi>T</mi><mo>)</mo></mrow><mo>∣</mo><mi>T</mi><mo>∈</mo><mi>SPIT</mi><mrow><mo>(</mo><mi>α</mi><mo>)</mo></mrow><mo>}</mo></mrow></math></span> and <span><math><mrow><mo>{</mo><msub><mrow><mi>w</mi></mrow><mrow><mi>r</mi></mrow></msub><mrow><mo>(</mo><mi>T</mi><mo>)</mo></mrow><mo>∣</mo><mi>T</mi><mo>∈</mo><mi>SPIT</mi><mrow><mo>(</mo><mi>α</mi><mo>)</mo></mrow><mo>}</mo></mrow></math></span> share identical descent distributions. Here, <span><math><mrow><mi>SPIT</mi><mrow><mo>(</mo><mi>α</mi><mo>)</mo></mrow></mrow></math></span> is the set of standard peak immaculate tableaux of shape <span><math><mi>α</mi></math></span>, and <span><math><msub><mrow><mi>w</mi></mrow><mrow><mi>c</mi></mrow></msub></math></span> and <span><math><msub><mrow><mi>w</mi></mrow><mrow><mi>r</mi></mrow></msub></math></span> denote column reading and row reading, respectively. By combining this equidistribution with the algorithm developed by Allen, Hallam, and Mason, we demonstrate that the transition matrix from the basis of quasisymmetric Schur <span><math><mi>Q</mi></math></span>-functions to the basis of peak Young quasisymmetric Schur functions is upper triangular, with entries being non-negative integers. Furthermore, we provide explicit descriptions of the expansion of peak Young quasisymmetric Schur functions in specific cases, in terms of quasisymmetric Schur <span><math><mi>Q</mi></math></span>-functions. We also investigate the combinatorial properties of standard peak immaculate tableaux, standard Young composition tableaux, and standard peak Young composition tableaux. We provide a hook length formula for <span><math><mrow><mi>SPIT</mi><mrow><mo>(</mo><mi>α</mi><mo>)</mo></mrow></mrow></math></span> and show that standard Young composition tableaux and standard peak Young composition tableaux can be each bijectively mapped to words satisfying suitable conditions. Especially, cases of compositions with rectangular shape are examined in detail.</div></div>","PeriodicalId":50490,"journal":{"name":"European Journal of Combinatorics","volume":"130 ","pages":"Article 104213"},"PeriodicalIF":1.0,"publicationDate":"2025-07-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144571712","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Beyond the pseudoforest strong Nine Dragon Tree Theorem 超越伪林强九龙树定理
IF 1 3区 数学
European Journal of Combinatorics Pub Date : 2025-07-08 DOI: 10.1016/j.ejc.2025.104214
Sebastian Mies , Benjamin Moore , Evelyne Smith-Roberge
{"title":"Beyond the pseudoforest strong Nine Dragon Tree Theorem","authors":"Sebastian Mies ,&nbsp;Benjamin Moore ,&nbsp;Evelyne Smith-Roberge","doi":"10.1016/j.ejc.2025.104214","DOIUrl":"10.1016/j.ejc.2025.104214","url":null,"abstract":"<div><div>The pseudoforest version of the Strong Nine Dragon Tree Conjecture states that if a graph <span><math><mi>G</mi></math></span> has maximum average degree <span><math><mrow><mi>m</mi><mi>a</mi><mi>d</mi><mrow><mo>(</mo><mi>G</mi><mo>)</mo></mrow><mo>=</mo><mn>2</mn><msub><mrow><mo>max</mo></mrow><mrow><mi>H</mi><mo>⊆</mo><mi>G</mi></mrow></msub><mfrac><mrow><mi>e</mi><mrow><mo>(</mo><mi>H</mi><mo>)</mo></mrow></mrow><mrow><mi>v</mi><mrow><mo>(</mo><mi>H</mi><mo>)</mo></mrow></mrow></mfrac></mrow></math></span> at most <span><math><mrow><mn>2</mn><mrow><mo>(</mo><mi>k</mi><mo>+</mo><mfrac><mrow><mi>d</mi></mrow><mrow><mi>d</mi><mo>+</mo><mi>k</mi><mo>+</mo><mn>1</mn></mrow></mfrac><mo>)</mo></mrow></mrow></math></span>, then it has a decomposition into <span><math><mrow><mi>k</mi><mo>+</mo><mn>1</mn></mrow></math></span> pseudoforests where in one pseudoforest <span><math><mi>F</mi></math></span> the components of <span><math><mi>F</mi></math></span> have at most <span><math><mi>d</mi></math></span> edges. This was proven in 2020 in Grout and Moore (2020). We strengthen this theorem by showing that we can find such a decomposition where additionally <span><math><mi>F</mi></math></span> is acyclic, the diameter of the components of <span><math><mi>F</mi></math></span> is at most <span><math><mrow><mn>2</mn><mi>ℓ</mi><mo>+</mo><mn>2</mn></mrow></math></span>, where <span><math><mrow><mi>ℓ</mi><mo>=</mo><mfenced><mrow><mfrac><mrow><mi>d</mi><mo>−</mo><mn>1</mn></mrow><mrow><mi>k</mi><mo>+</mo><mn>1</mn></mrow></mfrac></mrow></mfenced></mrow></math></span>, and at most <span><math><mrow><mn>2</mn><mi>ℓ</mi><mo>+</mo><mn>1</mn></mrow></math></span> if <span><math><mrow><mi>d</mi><mo>≡</mo><mn>1</mn><mspace></mspace><mo>mod</mo><mspace></mspace><mrow><mo>(</mo><mi>k</mi><mo>+</mo><mn>1</mn><mo>)</mo></mrow></mrow></math></span>. Furthermore, for any component <span><math><mi>K</mi></math></span> of <span><math><mi>F</mi></math></span> and any <span><math><mrow><mi>z</mi><mo>∈</mo><mi>N</mi></mrow></math></span>, we have <span><math><mrow><mi>d</mi><mi>i</mi><mi>a</mi><mi>m</mi><mrow><mo>(</mo><mi>K</mi><mo>)</mo></mrow><mo>≤</mo><mn>2</mn><mi>z</mi></mrow></math></span> if <span><math><mrow><mi>e</mi><mrow><mo>(</mo><mi>K</mi><mo>)</mo></mrow><mo>≥</mo><mi>d</mi><mo>−</mo><mi>z</mi><mrow><mo>(</mo><mi>k</mi><mo>−</mo><mn>1</mn><mo>)</mo></mrow><mo>+</mo><mn>1</mn></mrow></math></span>. We also show that both diameter bounds are best possible as an extension for both the Strong Nine Dragon Tree Conjecture for pseudoforests and its original conjecture for forests. In fact, they are still optimal even if we only enforce <span><math><mi>F</mi></math></span> to have any constant maximum degree, instead of enforcing every component of <span><math><mi>F</mi></math></span> to have at most <span><math><mi>d</mi></math></span> edges.</div></div>","PeriodicalId":50490,"journal":{"name":"European Journal of Combinatorics","volume":"130 ","pages":"Article 104214"},"PeriodicalIF":1.0,"publicationDate":"2025-07-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144579675","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
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