可数强F紧集的刻画与性质

借助α-ω聚点与α-聚点概念给出可数强F紧集的两个刻画定理,进而讨论可数强F紧集在L值Zadeh型函数下的逆不变性,证明了可数强F紧集与强F紧集的乘积是可数强F紧的。     

Fuzzy序列紧性,可数Fuzzy紧性和Fuzzy列紧性

本文引进了Fuzzy序列紧性、可数Fuzzy紧性和Fuzzy列紧性,它们是一般拓扑学中相应概念的“良扩张”(R. Lowen意义下),文中讨论了这些fts的主要性质,以及它们之间的联系。     

L－Fuzzy拓扑空间中一种新型的强F仿紧性

本文引入一种新型的强Ｆ仿紧性─—Ⅲ型强Ｆ仿紧性，它是基于α－局部有限族概念提出的，这种α－局部有限族概念可用于刻划强Ｆ可数紧性。     

可数Fuzzy紧集的性质

讨论可数Fuzzy紧集在L值Zadeh型函数下的逆不变性,证明可数Fuzzy紧集与Fuzzy紧集的乘积是可数Fuzzy紧的。     

L-模糊集的可数starplus-紧性

本文研究了在L-拓扑空间中,利用L-拓扑的水平拓扑引入可数starplus-紧性的概念,获得了可数starplus-紧性的性质,并且对一般拓扑中可数starplus-紧性的推广.     

超序列紧fts,可数超紧fts和超列紧fts

文献[1]中定义了序列紧fts(每个不分明集序列有收敛的子序列)和可数紧fts(每个可数开覆盖存在有限子覆盖)。对于序列紧fts,得到“每个fts都是序列紧的”病态结果,由此可见这样定义的序列紧fts不是一般拓扑学中序列紧的良扩张。对于可数紧fts,[2]在评论F-紧性时,论证了凡T_1空间都不是F-紧空间,以上的论证也可得到凡T_1空间都不是可数紧fts的病态结果。我们还要指出,[1]定义的可数紧fts也不是一般拓扑学中可数紧的良扩张。     

一种新的可数紧性

在L-fuzzy拓扑空间上，研究了可数S^＊-紧和可数S-紧的相关性质和特征。并就可数S^＊-紧、可数S-紧以及S-Lindeloef性质三者之间的关系进行了研究，得到了满足S-Lindeloef性质的可数S^＊-紧空间为S^＊-紧空间等结论。     

L—Fuzzy拓扑空间中的可数SR—紧性

从层次结构入手引入L－fuzzy拓扑空间中的可数SR－紧性,证明了可数SR－紧性对强半闭子集遗传,可数SR－紧子集在S－不定映射 像保持,给出了可数SR－紧性的几何刻画与有限交性质的刻画。     

L-fuzzy拓扑空间中的几乎可数仿紧性

以可数仿紧性为背景,介绍几乎可数仿紧性的定义,并刻画其基本特征.深入研究L-fuzzy几乎可数仿紧性的性质,并证明几乎可敷仿紧性是"L-好的推广".     

正规可数仿紧空间的逆极限

得到了如下结果:设X是逆系统{Xα,παβ,Λ}的逆极限,|Λ|=λ,假设每个映射πα∶X→Xα是开的且到上的,X是λ-仿紧,每个Xα是正规可数仿紧的,则X是正规可数仿紧的.进一步得到了关于遗传正规且遗传可数仿紧空间的类似结果.     

Characterisation of compactness through convergence in Tychonoff spaces

In this article we first give a characterisation of compact spaces among spaces by improving a theorem of J. Ewert. Then, with the aid of a new type of convergence, we give a characterisation of the pseudocompact and of the Lindelöf spaces.

     

Strongly almost disjoint sets and weakly uniform bases

A combinatorial principle CECA is formulated and its equivalence with GCH + certain weakenings of for singular is proved. CECA is used to show that certain ``almost point-' families can be refined to point- families by removing a small set from each member of the family. This theorem in turn is used to show the consistency of ``every first countable -space with a weakly uniform base has a point-countable base.'

     

Utility Representations of Preferences on General Choice Spaces

The purpose of this paper is to reconsider the utility representation problem of preferences. Several representation theorems are obtained on general choice spaces. Preferences having continuous utility functions are characterized by their continuities and countable satiation. It is showed that on a pairwise separable choice space,the sufficient and necessary condition for a preference to be represented by a continuous utility function is that the preference is continuous and countably satiable. For monotone preferences,we obtain that any space has continuous utility representations.     

On a Property of Urysohn's Universal Metric Space

Mathematical Notes -     

群元值测度的一个定义和一些性质

文中给出了定义在第二可数完备布尔代数上,取值于半序交换群内的群元值测度的一个定义和一些性质.     

三维流形上的近余辛$p$-球和近余辛度量双结构

本文主要研究近余辛$p$-球和近余辛度量双结构.首先给出近余辛$p$-球的性质.其次定义了近余辛度量双结构并给出其在三维流形上的相关结论.最后分析当$(1,1)$-型张量$h_1$和$h_2$满足codazzi type 和 cyclic parallel 时具有近余辛度量双结构的三维流形的性质.     

On countable connected locally connected almost regular Urysohn spaces

We construct connected, locally connected, almost regular, countable, Urysohn spaces. This answers a problem of G.X. Ritter. We show that there are 2^c such non-homeomorphic spaces. We also show that there are 2^c non-homeomorphic spaces which are further rigid. We discuss the group of homeomorphisms of such spaces.The following question was raised by G.X. Ritter: Does there exist a countable connected locally connected Urysohn space which is almost regular? We answer this question in the affirmative and in fact, show that not only are there as many as 2^c such spaces but that there are just as many rigid spaces with the same properties. Furthermore we show that every countable Urysohn space is a subspace of such a space. We also prove that every countable group is isomorphic to the group of autohomeomorphisms of some connected locally connected almost regular Urysohn space. Examples are given of groups of order c which can be represented in this manner.     

关于可数点集的盒维数的一些探讨

本文研究了一类可数点集的盒维数的计算问题.通过构造双Lipschitz映射,把原可数点集的盒维数的求解问题转化为求解一类相对简单的可数点集的盒维数.获得了两个单调的可数点集在具有同阶间隔时具有相同的上盒维数和下盒维数的结论.该结论为计算一类可数点集的盒维数提供了方便.     

On the bounded closure of the range of an operator

The ``bounded closure of the range" of an operator between two normed spaces is a linear subspace lying between the range and its closure. The induced concept of ``almost onto" is a sort of first draft of the concept of ``almost open".

     

一类广义幂零群

This paper considers such a group G which possesses nontrivial proper subgroups H 1 ,H 2 such that any proper subgroup of G not contained in H 1 ∪ H 2 is p-closed and obtains that if G is soluble,then the number of prime divisors contained in ｜G｜ is 2,3 or 4;if not,then it has a form x N where N/Φ（N） is a non-abelian simple group.Then the structure of such a group is determined for p = 2,H 1 = H 2 under some conditions.