关于序列覆盖紧映射

本文利用了ｃｓ网、序列邻域网、序列开网和弱基的概念,讨论了空间中点正则覆盖,一致覆盖和点有限覆盖的点星网之间的关系．建立了度量空间在几类序列覆盖（紧）映射下象空间的特征,特别地证明了度量空间的序列覆盖（或１序列覆盖）紧映象等价于具有点正则ｃｓ网的空问,回答了Ｔａｎａｋａ等提出的一个问题．     

关于序列覆盖s映射

本文定义了两类序列覆盖映射，讨论了度晴空间的序列覆盖ｓ映象，特别地，我们证明了空间Ｘ具有点可数弱当且仅当Ｘ是度量空间的１序列覆盖的商ｓ映象，这回答了１９７０年Ｔ．Ｈｏｓｈｉｎａ提出了一个问题。     

关于序列覆盖s映射的注记

本文分别给出局部可分度量空间的强序列覆盖（1序列覆盖,2序列覆盖）。映象的新刻画,还分别给出拓扑空间是局部可分度量空间的序列覆盖（紧覆盖）s映象的一个充分条件．     

一致覆盖和度量空间的紧映象

本文利用一致覆盖的概念,讨论了度量空间的序列覆盖紧映象的结构.主要结果有: (1)空间X是局部可分度量空间的序列覆盖紧映象当且仅当X具有由cosmic子空间构成的一致sn网; (2)空间X是局部可分度量空间的序列覆盖,商紧映象当且仅当X是度量空间的序列覆盖,商紧映象且是局部cosmic空间.     

度量空间的序列覆盖cs-π映象

给出了度量空间的1-序列覆盖、cs-π映象,2-序列覆盖、cs-π映象和子序列覆盖、cs-π映象的内在刻画.同时得到了度量空间的商cs-π映象的内在特征.     

星可数κ网与序列覆盖S映射

证明了在空间具有星可数κ网的条件下,度量空间的1(2)序列覆盖s映象是局部可分度量空间的1(2)序列覆盖、紧覆盖s映象.     

关于序列覆盖π映射

本文利用点星网的概念,讨论了度量空间的π映象的性质,建立了度量空间的序列商π映象和度量空间的序列覆盖π映象的内在特征,分别推广了 Kofner J、A.和 Tanaka Y.的一些结果.     

度量空间的1序列覆盖cs-π映象

本文建立度量空间1序列覆盖cs-π映象与度量空间紧覆盖cs-π映象的内在刻画．     

关于局部可数网与ss映射

本文建立了度量空间在几类序列覆盖ss映射下象空间的特征,讨论了局部可数集族与局部可数基（弱基）之间的相互关系,特别地证明了几类具有特定性质的局部可数网的正则空间与度量空间的几类序列覆盖ss映象之间相互等价,回答了Tanaka提出的一个问题．     

局部可分度量空间的伪序列覆盖映射

指出了文[1]中的一个问题,并给出了局部可分度量空间的伪序列覆盖s映象和局部可分度量空间的伪序列覆盖紧映象的刻划。     

Some Characterizations of Spaces with Weak Form of $cs$-Networks

In this paper, we introduce the concept of statistically sequentially quotient map:A mapping f : X → Y is statistically sequentially quotient map if whenever a convergent sequence S in Y, there is a convergent sequence L in X such that f(L) is statistically dense in S. Also, we discuss the relation between statistically sequentially quotient map and covering maps by characterizing statistically sequentially quotient map and we prove that every closed and statistically sequentially quotient image of a g-metrizable space is g-metrizable. Moreover,we discuss about the preservation of generalization of metric space in terms of weakbases and sn-networks by closed and statistically sequentially quotient map.     

关于1-序列商映射

引进了1-序列商映射，证明了1-序列商映射象保持sm-第一可数空间．作为这一结果的一个应用，本文证明了几乎开，闭映射保持度量空间，g-度量空间，sm-度量空间．此外本文还证明了度量空间上的1-序列商，紧映射是1-序列覆盖映射．这些结果改进并推广了广义度量空间映射象的有关理论．     

连通度量空间的映象

拓扑空间X称为s连通,若X不能表示为两个非空的不相交的序列开集之并.本文纠正了A.Fedeli 和A.Le Donne关于连通度量空间映象的错误论证,证明了s连通性可刻画为连通度量空间的连续的序列覆盖映象,从而导出连通的序列空间(或FrEchet空间)可刻画为连通度量空间的商映象(或伪开映象),回答了V.V.Tkachuk在Proc.Amer.Math Soc.上提出的问题.     

Compact images of spaces with a weaker metric topology

If X is a space that can be mapped onto a metric space by a one-to-one mapping, then X is said to have a weaker metric topology. In this paper, we give characterizations of sequence-covering compact images and sequentially-quotient compact images of spaces with a weaker metric topology. The main results are that (1) Y is a sequence-covering compact image of a space with a weaker metric topology if and only if Y has a sequence of point-finite cs-covers such that for each y ∈ Y. (2) Y is a sequentially-quotient compact image of a space with a weaker metric topology if and only if Y has a sequence of point-finite cs*-covers such that for each y ∈ Y. Supported by the NNSF(10471084) of China.     

Invariant approximations for commuting mappings in CAT(0) and hyperconvex spaces

In this paper, for a commuting pair consisting of a point-valued nonexpansive self-mapping t and a set-valued nonexpansive self-mapping T of a hyperconvex metric space (or a CAT(0) space) X, we look for a solution to the problem of existence of z∈E⊂X such that

     

伪群作用与覆盖空间

证明了如果U是一个黎曼流形的子集,伪群G作用在它上面,若这个伪作用是第一类的,那么覆盖空间方法给出了U/G的一个正规覆盖空间;若X是一个局部紧的长度空间X,且伪群H在X的一个度量球上的作用是第二类的,则构造出来的空间是X的一个正规覆盖空间.另外,还证明了对于两类流形,存在切球上的由道路提升定义的第一类伪作用.     

A note on closed images of locally compact metric spaces

Summary A decomposition theorem about closed images of locally compact metric spaces is discussed. It is shown that a space is a closed image of a locally compact metric space if and only if it is a regular Fréchet space with a point-countable k-network, and each of its closed first-countable subset is locally compact.