European Journal of Combinatorics最新文献_第4页

Hypercube minor-universality 超立方体minor-universality

IF 0.9 3区数学

European Journal of Combinatorics Pub Date : 2026-03-01 Epub Date: 2025-12-16 DOI: 10.1016/j.ejc.2025.104317

Itai Benjamini, Or Bernard Kalifa, Elad Tzalik

引用次数: 0

A characterization of the Grassmann graphs: One missing case 格拉斯曼图的表征：一个缺失的情况

IF 0.9 3区数学

European Journal of Combinatorics Pub Date : 2026-03-01 Epub Date: 2025-12-20 DOI: 10.1016/j.ejc.2025.104320

Jack H. Koolen , Chenhui Lv , Alexander L. Gavrilyuk

引用次数: 0

Generalized quasikernels in digraphs 有向图中的广义拟核

IF 0.9 3区数学

European Journal of Combinatorics Pub Date : 2026-03-01 Epub Date: 2025-12-20 DOI: 10.1016/j.ejc.2025.104307

Sam Spiro

引用次数: 0

Unbounded matroids 无限的拟阵

IF 0.9 3区数学

European Journal of Combinatorics Pub Date : 2026-03-01 Epub Date: 2025-12-04 DOI: 10.1016/j.ejc.2025.104298

Jonah Berggren , Jeremy L. Martin , José A. Samper

{"title":"Unbounded matroids","authors":"Jonah Berggren , Jeremy L. Martin , José A. Samper","doi":"10.1016/j.ejc.2025.104298","DOIUrl":"10.1016/j.ejc.2025.104298","url":null,"abstract":"<div><div>A matroid base polytope is a polytope in which each vertex has 0,1 coordinates and each edge is parallel to a difference of two coordinate vectors. Matroid base polytopes are described combinatorially by integral submodular functions on a boolean lattice, satisfying the unit increase property. We define a more general class of <em>unbounded matroids</em>, or <em>U-matroids</em>, by replacing the boolean lattice with an arbitrary distributive lattice. U-matroids thus serve as a combinatorial model for polyhedra that satisfy the vertex and edge conditions of matroid base polytopes, but may be unbounded. Like polymatroids, U-matroids generalize matroids and arise as a special case of submodular systems. We prove that every U-matroid admits a canonical largest extension to a matroid, which we call the <em>generous extension</em>; the analogous geometric statement is that every U-matroid base polyhedron contains a unique largest matroid base polytope. We show that the supports of vertices of a U-matroid base polyhedron span a shellable simplicial complex, and we characterize U-matroid basis systems in terms of shelling orders, generalizing Björner’s and Gale’s criteria for a simplicial complex to be a matroid independence complex. Finally, we present an application of our theory to subspace arrangements and show that the generous extension has a natural geometric interpretation in this setting.</div></div>","PeriodicalId":50490,"journal":{"name":"European Journal of Combinatorics","volume":"133 ","pages":"Article 104298"},"PeriodicalIF":0.9,"publicationDate":"2026-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145685592","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

Fragile minor-monotone parameters under a random edge perturbation 随机边缘扰动下的脆弱次单调参数

IF 0.9 3区数学

European Journal of Combinatorics Pub Date : 2026-03-01 Epub Date: 2025-12-04 DOI: 10.1016/j.ejc.2025.104305

Dong Yeap Kang , Mihyun Kang , Jaehoon Kim , Sang-il Oum

引用次数: 0

A spectral lower bound on chromatic numbers using p-energy 利用p能量的色数的谱下界

IF 0.9 3区数学

European Journal of Combinatorics Pub Date : 2026-02-01 Epub Date: 2025-10-13 DOI: 10.1016/j.ejc.2025.104252

Clive Elphick , Quanyu Tang , Shengtong Zhang

引用次数: 0

An identity relating Catalan numbers to tangent numbers with arithmetic applications 加泰罗尼亚数与正切数之间的恒等式及其算术应用

IF 0.9 3区数学

European Journal of Combinatorics Pub Date : 2026-02-01 Epub Date: 2025-11-13 DOI: 10.1016/j.ejc.2025.104283

Tongyuan Zhao , Zhicong Lin , Yongchun Zang

引用次数: 0

A bijection for descent sets of permutations with only even and only odd cycles 只有偶圈和奇圈的置换下降集的双射

IF 0.9 3区数学

European Journal of Combinatorics Pub Date : 2026-02-01 Epub Date: 2025-11-10 DOI: 10.1016/j.ejc.2025.104280

Sergi Elizalde

{"title":"A bijection for descent sets of permutations with only even and only odd cycles","authors":"Sergi Elizalde","doi":"10.1016/j.ejc.2025.104280","DOIUrl":"10.1016/j.ejc.2025.104280","url":null,"abstract":"<div><div>It is known that, when <span><math><mi>n</mi></math></span> is even, the number of permutations of <span><math><mrow><mo>{</mo><mn>1</mn><mo>,</mo><mn>2</mn><mo>,</mo><mo>…</mo><mo>,</mo><mi>n</mi><mo>}</mo></mrow></math></span> all of whose cycles have odd length equals the number of those all of whose cycles have even length. Adin, Hegedűs and Roichman recently found a surprising refinement of this identity. They showed that, for any fixed set <span><math><mi>J</mi></math></span>, the equality still holds when restricting to permutations with descent set <span><math><mi>J</mi></math></span> on one side, and permutations with ascent set <span><math><mi>J</mi></math></span> on the other. Their proof uses generating functions for higher Lie characters, and it also yields a version for odd <span><math><mi>n</mi></math></span>. Here we give a bijective proof of their result. We first use known bijections, due to Gessel, Reutenauer and others, to restate the identity in terms of multisets of necklaces, which we interpret as words, and then describe a new weight-preserving bijection between words all of whose Lyndon factors have odd length and are distinct, and words all of whose Lyndon factors have even length. We also show that the corresponding equality about Lyndon factorizations has a short proof using generating functions.</div></div>","PeriodicalId":50490,"journal":{"name":"European Journal of Combinatorics","volume":"132 ","pages":"Article 104280"},"PeriodicalIF":0.9,"publicationDate":"2026-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145528894","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

Intervals in the Hales–Jewett theorem Hales-Jewett定理中的区间

IF 0.9 3区数学

European Journal of Combinatorics Pub Date : 2026-02-01 Epub Date: 2025-10-21 DOI: 10.1016/j.ejc.2025.104258

David Conlon , Nina Kamčev

{"title":"Intervals in the Hales–Jewett theorem","authors":"David Conlon , Nina Kamčev","doi":"10.1016/j.ejc.2025.104258","DOIUrl":"10.1016/j.ejc.2025.104258","url":null,"abstract":"<div><div>The Hales–Jewett theorem states that for any <span><math><mi>m</mi></math></span> and <span><math><mi>r</mi></math></span> there exists an <span><math><mi>n</mi></math></span> such that any <span><math><mi>r</mi></math></span>-colouring of the elements of <span><math><msup><mrow><mrow><mo>[</mo><mi>m</mi><mo>]</mo></mrow></mrow><mrow><mi>n</mi></mrow></msup></math></span> contains a monochromatic combinatorial line. We study the structure of the wildcard set <span><math><mrow><mi>S</mi><mo>⊆</mo><mrow><mo>[</mo><mi>n</mi><mo>]</mo></mrow></mrow></math></span> which determines this monochromatic line, showing that when <span><math><mi>r</mi></math></span> is odd there are <span><math><mi>r</mi></math></span>-colourings of <span><math><msup><mrow><mrow><mo>[</mo><mn>3</mn><mo>]</mo></mrow></mrow><mrow><mi>n</mi></mrow></msup></math></span> where the wildcard set of a monochromatic line cannot be the union of fewer than <span><math><mi>r</mi></math></span> intervals. This is tight, as for <span><math><mi>n</mi></math></span> sufficiently large there are always monochromatic lines whose wildcard set is the union of at most <span><math><mi>r</mi></math></span> intervals.</div></div>","PeriodicalId":50490,"journal":{"name":"European Journal of Combinatorics","volume":"132 ","pages":"Article 104258"},"PeriodicalIF":0.9,"publicationDate":"2026-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145623511","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

Twists and twistability 扭转和扭转能力

IF 0.9 3区数学

European Journal of Combinatorics Pub Date : 2026-02-01 Epub Date: 2025-10-30 DOI: 10.1016/j.ejc.2025.104259

Rebecca Coulson

引用次数: 0