József Balogh , Ramon I. Garcia , Lina Li , Adam Zsolt Wagner
{"title":"Intersecting families of sets are typically trivial","authors":"József Balogh , Ramon I. Garcia , Lina Li , Adam Zsolt Wagner","doi":"10.1016/j.jctb.2023.09.002","DOIUrl":null,"url":null,"abstract":"<div><p>A family of subsets of <span><math><mo>[</mo><mi>n</mi><mo>]</mo></math></span> is <em>intersecting</em> if every pair of its sets intersects. Determining the structure of large intersecting families is a central problem in extremal combinatorics. Frankl–Kupavskii and Balogh–Das–Liu–Sharifzadeh–Tran showed that for <span><math><mi>n</mi><mo>≥</mo><mn>2</mn><mi>k</mi><mo>+</mo><mi>c</mi><msqrt><mrow><mi>k</mi><mi>ln</mi><mo></mo><mi>k</mi></mrow></msqrt></math></span>, almost all <em>k</em>-uniform intersecting families are stars. Improving their result, we show that the same conclusion holds for <span><math><mi>n</mi><mo>≥</mo><mn>2</mn><mi>k</mi><mo>+</mo><mn>100</mn><mi>ln</mi><mo></mo><mi>k</mi></math></span>. Our proof uses, among others, the graph container method and the Das–Tran removal lemma.</p></div>","PeriodicalId":54865,"journal":{"name":"Journal of Combinatorial Theory Series B","volume":"164 ","pages":"Pages 44-67"},"PeriodicalIF":1.2000,"publicationDate":"2023-09-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"4","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of Combinatorial Theory Series B","FirstCategoryId":"100","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0095895623000709","RegionNum":1,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"MATHEMATICS","Score":null,"Total":0}
引用次数: 4
Abstract
A family of subsets of is intersecting if every pair of its sets intersects. Determining the structure of large intersecting families is a central problem in extremal combinatorics. Frankl–Kupavskii and Balogh–Das–Liu–Sharifzadeh–Tran showed that for , almost all k-uniform intersecting families are stars. Improving their result, we show that the same conclusion holds for . Our proof uses, among others, the graph container method and the Das–Tran removal lemma.
期刊介绍:
The Journal of Combinatorial Theory publishes original mathematical research dealing with theoretical and physical aspects of the study of finite and discrete structures in all branches of science. Series B is concerned primarily with graph theory and matroid theory and is a valuable tool for mathematicians and computer scientists.