{"title":"相交超图中的破碎匹配","authors":"P. Frankl, J. Pach","doi":"10.2140/MOSCOW.2021.10.49","DOIUrl":null,"url":null,"abstract":"Let $X$ be an $n$-element set, where $n$ is even. We refute a conjecture of J. Gordon and Y. Teplitskaya, according to which, for every maximal intersecting family $\\mathcal{F}$ of $\\frac{n}2$-element subsets of $X$, one can partition $X$ into $\\frac{n}2$ disjoint pairs in such a way that no matter how we pick one element from each of the first $\\frac{n}2 - 1$ pairs, the set formed by them can always be completed to a member of $\\mathcal{F}$ by adding an element of the last pair. \nThe above problem is related to classical questions in extremal set theory. For any $t\\ge 2$, we call a family of sets $\\mathcal{F}\\subset 2^X$ {\\em $t$-separable} if for any ordered pair of elements $(x,y)$ of $X$, there exists $F\\in\\mathcal{F}$ such that $F\\cap\\{x,y\\}=\\{x\\}$. For a fixed $t, 2\\le t\\le 5$ and $n\\rightarrow\\infty$, we establish asymptotically tight estimates for the smallest integer $s=s(n,t)$ such that every family $\\mathcal{F}$ with $|\\mathcal{F}|\\ge s$ is $t$-separable.","PeriodicalId":36590,"journal":{"name":"Moscow Journal of Combinatorics and Number Theory","volume":" ","pages":""},"PeriodicalIF":0.0000,"publicationDate":"2020-05-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Shattered matchings in intersecting hypergraphs\",\"authors\":\"P. Frankl, J. Pach\",\"doi\":\"10.2140/MOSCOW.2021.10.49\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"Let $X$ be an $n$-element set, where $n$ is even. We refute a conjecture of J. Gordon and Y. Teplitskaya, according to which, for every maximal intersecting family $\\\\mathcal{F}$ of $\\\\frac{n}2$-element subsets of $X$, one can partition $X$ into $\\\\frac{n}2$ disjoint pairs in such a way that no matter how we pick one element from each of the first $\\\\frac{n}2 - 1$ pairs, the set formed by them can always be completed to a member of $\\\\mathcal{F}$ by adding an element of the last pair. \\nThe above problem is related to classical questions in extremal set theory. For any $t\\\\ge 2$, we call a family of sets $\\\\mathcal{F}\\\\subset 2^X$ {\\\\em $t$-separable} if for any ordered pair of elements $(x,y)$ of $X$, there exists $F\\\\in\\\\mathcal{F}$ such that $F\\\\cap\\\\{x,y\\\\}=\\\\{x\\\\}$. For a fixed $t, 2\\\\le t\\\\le 5$ and $n\\\\rightarrow\\\\infty$, we establish asymptotically tight estimates for the smallest integer $s=s(n,t)$ such that every family $\\\\mathcal{F}$ with $|\\\\mathcal{F}|\\\\ge s$ is $t$-separable.\",\"PeriodicalId\":36590,\"journal\":{\"name\":\"Moscow Journal of Combinatorics and Number Theory\",\"volume\":\" \",\"pages\":\"\"},\"PeriodicalIF\":0.0000,\"publicationDate\":\"2020-05-11\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Moscow Journal of Combinatorics and Number Theory\",\"FirstCategoryId\":\"1085\",\"ListUrlMain\":\"https://doi.org/10.2140/MOSCOW.2021.10.49\",\"RegionNum\":0,\"RegionCategory\":null,\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q4\",\"JCRName\":\"Mathematics\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Moscow Journal of Combinatorics and Number Theory","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.2140/MOSCOW.2021.10.49","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q4","JCRName":"Mathematics","Score":null,"Total":0}
Let $X$ be an $n$-element set, where $n$ is even. We refute a conjecture of J. Gordon and Y. Teplitskaya, according to which, for every maximal intersecting family $\mathcal{F}$ of $\frac{n}2$-element subsets of $X$, one can partition $X$ into $\frac{n}2$ disjoint pairs in such a way that no matter how we pick one element from each of the first $\frac{n}2 - 1$ pairs, the set formed by them can always be completed to a member of $\mathcal{F}$ by adding an element of the last pair.
The above problem is related to classical questions in extremal set theory. For any $t\ge 2$, we call a family of sets $\mathcal{F}\subset 2^X$ {\em $t$-separable} if for any ordered pair of elements $(x,y)$ of $X$, there exists $F\in\mathcal{F}$ such that $F\cap\{x,y\}=\{x\}$. For a fixed $t, 2\le t\le 5$ and $n\rightarrow\infty$, we establish asymptotically tight estimates for the smallest integer $s=s(n,t)$ such that every family $\mathcal{F}$ with $|\mathcal{F}|\ge s$ is $t$-separable.