以$\omega^{\omega}$为基的拓扑空间

IF 1.5 3区 数学 Q1 MATHEMATICS Dissertationes Mathematicae Pub Date : 2016-07-27 DOI:10.4064/dm762-4-2018
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。
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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
CiteScore
2.80
自引率
0.00%
发文量
8
审稿时长
>12 weeks
期刊介绍: DISSERTATIONES MATHEMATICAE publishes long research papers (preferably 50-100 pages) in any area of mathematics. An important feature of papers accepted for publication should be their utility for a broad readership of specialists in the domain. In particular, the papers should be to some reasonable extent self-contained. The paper version is considered as primary. The following criteria are taken into account in the reviewing procedure: correctness, mathematical level, mathematical novelty, utility for a broad readership of specialists in the domain, language and editorial aspects. The Editors have adopted appropriate procedures to avoid ghostwriting and guest authorship.
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