以$\omega^{\omega}$为基的拓扑空间

IF 16.4 1区 化学 Q1 CHEMISTRY, MULTIDISCIPLINARY
T. Banakh
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引用次数: 7

摘要

给定一个部分有序集$P$,我们研究了拓扑空间$X$的性质,允许$P$ -基,即$X\times X$的子集的索引族$(U_\alpha)_{\alpha\in P}$,使得$P$中所有$\alpha\le\beta$的$U_\beta\subset U_\alpha$,以及对于每个$x\in X$,球的$(U_\alpha[x])_{\alpha\in P}$的$U_\alpha[x]=\{y\in X:(x,y)\in U_\alpha\}$是$x$的邻基。如果随行人员家属$(U_\alpha U_\alpha^{-1}U_\alpha)_{\alpha\in P}$仍然是$X$的$P$ -base,则将$X$的$P$ -base $(U_\alpha)_{\alpha\in P}$称为本地统一的。当且仅当拓扑空间具有$\omega$ -基时,拓扑空间是可首数的。根据摩尔度量定理,一个拓扑空间是可度量的当且仅当它是一个具有局部一致$\omega$ -基的$T_0$ -空间。本文将研究具有(局部一致)$\omega^\omega$ -基的拓扑空间。我们的结果表明,具有$\omega^\omega$ -基的空间与第一可数空间具有一些共同的性质,特别是,对于基于$\omega^\omega$的可数紧拓扑空间,许多已知的第一可数空间基数的上界仍然为真。另一方面,具有局部一致$\omega^\omega$ -基的拓扑空间具有许多特性,这是广义度量空间的典型特征。研究了具有$\omega^\omega$ -基的Tychonoff空间的全称(前-或拟-)均匀性,并证明了这类空间接近于$\sigma$ -紧。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Topological spaces with an $\omega^{\omega}$-base
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.
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来源期刊
Accounts of Chemical Research
Accounts of Chemical Research 化学-化学综合
CiteScore
31.40
自引率
1.10%
发文量
312
审稿时长
2 months
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.
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