{"title":"以$\\omega^{\\omega}$为基的拓扑空间","authors":"T. Banakh","doi":"10.4064/dm762-4-2018","DOIUrl":null,"url":null,"abstract":"Given a partially ordered set $P$ we study properties of topological spaces $X$ admitting a $P$-base, i.e., an indexed family $(U_\\alpha)_{\\alpha\\in P}$ of subsets of $X\\times X$ such that $U_\\beta\\subset U_\\alpha$ for all $\\alpha\\le\\beta$ in $P$ and for every $x\\in X$ the family $(U_\\alpha[x])_{\\alpha\\in P}$ of balls $U_\\alpha[x]=\\{y\\in X:(x,y)\\in U_\\alpha\\}$ is a neighborhood base at $x$. A $P$-base $(U_\\alpha)_{\\alpha\\in P}$ for $X$ is called locally uniform if the family of entourages $(U_\\alpha U_\\alpha^{-1}U_\\alpha)_{\\alpha\\in P}$ remains a $P$-base for $X$. A topological space is first-countable if and only if it has an $\\omega$-base. By Moore's Metrization Theorem, a topological space is metrizable if and only if it is a $T_0$-space with a locally uniform $\\omega$-base. \nIn the paper we shall study topological spaces possessing a (locally uniform) $\\omega^\\omega$-base. Our results show that spaces with an $\\omega^\\omega$-base share some common properties with first countable spaces, in particular, many known upper bounds on the cardinality of first-countable spaces remain true for countably tight $\\omega^\\omega$-based topological spaces. On the other hand, topological spaces with a locally uniform $\\omega^\\omega$-base have many properties, typical for generalized metric spaces. Also we study Tychonoff spaces whose universal (pre- or quasi-) uniformity has an $\\omega^\\omega$-base and show that such spaces are close to being $\\sigma$-compact.","PeriodicalId":1,"journal":{"name":"Accounts of Chemical Research","volume":null,"pages":null},"PeriodicalIF":16.4000,"publicationDate":"2016-07-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"7","resultStr":"{\"title\":\"Topological spaces with an $\\\\omega^{\\\\omega}$-base\",\"authors\":\"T. Banakh\",\"doi\":\"10.4064/dm762-4-2018\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"Given a partially ordered set $P$ we study properties of topological spaces $X$ admitting a $P$-base, i.e., an indexed family $(U_\\\\alpha)_{\\\\alpha\\\\in P}$ of subsets of $X\\\\times X$ such that $U_\\\\beta\\\\subset U_\\\\alpha$ for all $\\\\alpha\\\\le\\\\beta$ in $P$ and for every $x\\\\in X$ the family $(U_\\\\alpha[x])_{\\\\alpha\\\\in P}$ of balls $U_\\\\alpha[x]=\\\\{y\\\\in X:(x,y)\\\\in U_\\\\alpha\\\\}$ is a neighborhood base at $x$. A $P$-base $(U_\\\\alpha)_{\\\\alpha\\\\in P}$ for $X$ is called locally uniform if the family of entourages $(U_\\\\alpha U_\\\\alpha^{-1}U_\\\\alpha)_{\\\\alpha\\\\in P}$ remains a $P$-base for $X$. A topological space is first-countable if and only if it has an $\\\\omega$-base. By Moore's Metrization Theorem, a topological space is metrizable if and only if it is a $T_0$-space with a locally uniform $\\\\omega$-base. \\nIn the paper we shall study topological spaces possessing a (locally uniform) $\\\\omega^\\\\omega$-base. Our results show that spaces with an $\\\\omega^\\\\omega$-base share some common properties with first countable spaces, in particular, many known upper bounds on the cardinality of first-countable spaces remain true for countably tight $\\\\omega^\\\\omega$-based topological spaces. On the other hand, topological spaces with a locally uniform $\\\\omega^\\\\omega$-base have many properties, typical for generalized metric spaces. Also we study Tychonoff spaces whose universal (pre- or quasi-) uniformity has an $\\\\omega^\\\\omega$-base and show that such spaces are close to being $\\\\sigma$-compact.\",\"PeriodicalId\":1,\"journal\":{\"name\":\"Accounts of Chemical Research\",\"volume\":null,\"pages\":null},\"PeriodicalIF\":16.4000,\"publicationDate\":\"2016-07-27\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"7\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Accounts of Chemical Research\",\"FirstCategoryId\":\"100\",\"ListUrlMain\":\"https://doi.org/10.4064/dm762-4-2018\",\"RegionNum\":1,\"RegionCategory\":\"化学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q1\",\"JCRName\":\"CHEMISTRY, MULTIDISCIPLINARY\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Accounts of Chemical Research","FirstCategoryId":"100","ListUrlMain":"https://doi.org/10.4064/dm762-4-2018","RegionNum":1,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"CHEMISTRY, MULTIDISCIPLINARY","Score":null,"Total":0}
Given a partially ordered set $P$ we study properties of topological spaces $X$ admitting a $P$-base, i.e., an indexed family $(U_\alpha)_{\alpha\in P}$ of subsets of $X\times X$ such that $U_\beta\subset U_\alpha$ for all $\alpha\le\beta$ in $P$ and for every $x\in X$ the family $(U_\alpha[x])_{\alpha\in P}$ of balls $U_\alpha[x]=\{y\in X:(x,y)\in U_\alpha\}$ is a neighborhood base at $x$. A $P$-base $(U_\alpha)_{\alpha\in P}$ for $X$ is called locally uniform if the family of entourages $(U_\alpha U_\alpha^{-1}U_\alpha)_{\alpha\in P}$ remains a $P$-base for $X$. A topological space is first-countable if and only if it has an $\omega$-base. By Moore's Metrization Theorem, a topological space is metrizable if and only if it is a $T_0$-space with a locally uniform $\omega$-base.
In the paper we shall study topological spaces possessing a (locally uniform) $\omega^\omega$-base. Our results show that spaces with an $\omega^\omega$-base share some common properties with first countable spaces, in particular, many known upper bounds on the cardinality of first-countable spaces remain true for countably tight $\omega^\omega$-based topological spaces. On the other hand, topological spaces with a locally uniform $\omega^\omega$-base have many properties, typical for generalized metric spaces. Also we study Tychonoff spaces whose universal (pre- or quasi-) uniformity has an $\omega^\omega$-base and show that such spaces are close to being $\sigma$-compact.
期刊介绍:
Accounts of Chemical Research presents short, concise and critical articles offering easy-to-read overviews of basic research and applications in all areas of chemistry and biochemistry. These short reviews focus on research from the author’s own laboratory and are designed to teach the reader about a research project. In addition, Accounts of Chemical Research publishes commentaries that give an informed opinion on a current research problem. Special Issues online are devoted to a single topic of unusual activity and significance.
Accounts of Chemical Research replaces the traditional article abstract with an article "Conspectus." These entries synopsize the research affording the reader a closer look at the content and significance of an article. Through this provision of a more detailed description of the article contents, the Conspectus enhances the article's discoverability by search engines and the exposure for the research.