{"title":"交换函数图的Borel色数","authors":"C. Meehan, Konstantinos Palamourdas","doi":"10.4064/fm577-5-2020","DOIUrl":null,"url":null,"abstract":"Let D = (X,D) be a Borel directed graph on a standard Borel space X and let χB(D) be its Borel chromatic number. If F0, . . . , Fn−1 : X → X are Borel functions, let DF0,...,Fn−1 be the directed graph that they generate. It is an open problem if χB(DF0,...,Fn−1) ∈ {1, . . . , 2n + 1,א0}. This was verified for commuting functions with no fixed points. We show here that for commuting functions with the properties that χB(DF0,...,Fn−1) < א0 and that there is a path from each x ∈ X to a fixed point of some Fj , there exists an increasing filtration {Xm}m<ω with X = ⋃ m<ωXm such that χB(DF0,...,Fn−1 Xm) ≤ 2n for each m. We also prove that if n = 2 in the previous case, then χB(DF0,F1) ≤ 4. It follows that the approximate measure chromatic number χ ap M (D) does not exceed 2n+ 1 when the functions commute.","PeriodicalId":55138,"journal":{"name":"Fundamenta Mathematicae","volume":"1 1","pages":""},"PeriodicalIF":0.5000,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Borel chromatic numbers of graphs of commuting functions\",\"authors\":\"C. Meehan, Konstantinos Palamourdas\",\"doi\":\"10.4064/fm577-5-2020\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"Let D = (X,D) be a Borel directed graph on a standard Borel space X and let χB(D) be its Borel chromatic number. If F0, . . . , Fn−1 : X → X are Borel functions, let DF0,...,Fn−1 be the directed graph that they generate. It is an open problem if χB(DF0,...,Fn−1) ∈ {1, . . . , 2n + 1,א0}. This was verified for commuting functions with no fixed points. We show here that for commuting functions with the properties that χB(DF0,...,Fn−1) < א0 and that there is a path from each x ∈ X to a fixed point of some Fj , there exists an increasing filtration {Xm}m<ω with X = ⋃ m<ωXm such that χB(DF0,...,Fn−1 Xm) ≤ 2n for each m. We also prove that if n = 2 in the previous case, then χB(DF0,F1) ≤ 4. It follows that the approximate measure chromatic number χ ap M (D) does not exceed 2n+ 1 when the functions commute.\",\"PeriodicalId\":55138,\"journal\":{\"name\":\"Fundamenta Mathematicae\",\"volume\":\"1 1\",\"pages\":\"\"},\"PeriodicalIF\":0.5000,\"publicationDate\":\"2021-01-01\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Fundamenta Mathematicae\",\"FirstCategoryId\":\"100\",\"ListUrlMain\":\"https://doi.org/10.4064/fm577-5-2020\",\"RegionNum\":3,\"RegionCategory\":\"数学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q3\",\"JCRName\":\"MATHEMATICS\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Fundamenta Mathematicae","FirstCategoryId":"100","ListUrlMain":"https://doi.org/10.4064/fm577-5-2020","RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q3","JCRName":"MATHEMATICS","Score":null,"Total":0}
引用次数: 0
摘要
设D = (X,D)为标准Borel空间X上的Borel有向图,设χB(D)为其Borel色数。如果F0,…, Fn−1:X→X为Borel函数,设DF0,…,Fn−1为它们生成的有向图。若χB(DF0,…,Fn−1)∈{1,…,则为开放问题。, 2n + 1, 0}。这在没有不动点的交换函数中得到了验证。我们证明了对于具有χB(DF0,…,Fn−1)< 0的交换函数,并且存在从每个x∈x到某个Fj的不动点的路径,存在一个增大过滤{Xm}m<ω, x =∈m<ωXm,使得χB(DF0,…),对于每个m,Fn−1 Xm)≤2n。我们也证明了如果在前一种情况下n = 2,则χB(DF0,F1)≤4。当函数交换时,近似测度色数χ ap M (D)不超过2n+ 1。
Borel chromatic numbers of graphs of commuting functions
Let D = (X,D) be a Borel directed graph on a standard Borel space X and let χB(D) be its Borel chromatic number. If F0, . . . , Fn−1 : X → X are Borel functions, let DF0,...,Fn−1 be the directed graph that they generate. It is an open problem if χB(DF0,...,Fn−1) ∈ {1, . . . , 2n + 1,א0}. This was verified for commuting functions with no fixed points. We show here that for commuting functions with the properties that χB(DF0,...,Fn−1) < א0 and that there is a path from each x ∈ X to a fixed point of some Fj , there exists an increasing filtration {Xm}m<ω with X = ⋃ m<ωXm such that χB(DF0,...,Fn−1 Xm) ≤ 2n for each m. We also prove that if n = 2 in the previous case, then χB(DF0,F1) ≤ 4. It follows that the approximate measure chromatic number χ ap M (D) does not exceed 2n+ 1 when the functions commute.
期刊介绍:
FUNDAMENTA MATHEMATICAE concentrates on papers devoted to
Set Theory,
Mathematical Logic and Foundations of Mathematics,
Topology and its Interactions with Algebra,
Dynamical Systems.