k-COVERS AND CERTAIN QUOTIENT IMAGES OF PARACOMPACT LOCALLY COMPACT SPACES

We continue to discuss some properties of certain k-covers. As applications, we give some characterizations of certain quotient images of paracompact locally compact spaces.     

Pseudocompact Whyburn spaces need not be Fréchet

We prove in ZFC that there exists a Tychonoff pseudocompact scattered AP-space of uncountable tightness. We give some sufficient and necessary conditions for a -space to be AP as well as a characterization of AP-property in linearly ordered topological spaces.

     

<Emphasis Type="Italic">LJ</Emphasis>-spaces

In this paper LJ-spaces are introduced and studied. They are a common generalization of Lindelöf spaces and J-spaces researched by E. Michael. A space X is called an LJ-space if, whenever {A, B} is a closed cover of X with A ∩ B compact, then A or B is Lindelöf. Semi-strong LJ-spaces and strong LJ-spaces are also defined and investigated. It is demonstrated that the three spaces are different and have interesting properties and behaviors.     

Index sets of decidable models

We study the index sets of the class of d-decidable structures and of the class of d-decidable countably categorical structures, where d is an arbitrary arithmetical Turing degree. It is proved that the first of them is m-complete ∑ ₃ ^{0, d} , and the second is m-complete ∑ ₃ ^{0, d} \∑ ₃ ^{0, d} in the universal computable numbering of computable structures for the language with one binary predicate.     

Countably compact groups from a selective ultrafilter

We prove that the existence of a selective ultrafilter on implies the existence of a countably compact group without non-trivial convergent sequences all of whose powers are countably compact. Hence, by using a selective ultrafilter on , it is possible to construct two countably compact groups without non-trivial convergent sequences whose product is not countably compact.

     

From countable compactness to absolute countable compactness

We show that every countably compact space which is monotonically normal, almost 2-fully normal, radial , or with countable spread is absolutely countably compact. For the first two mentioned properties, we prove more general results not requiring countable compactness. We also prove that every monotonically normal, orthocompact space is finitely fully normal.

     

The Orlicz-Pettis theorem for topological Riesz spaces

A finitely additive vector measure from a -ring to a Riesz space is countably additive (exhaustive) for all Hausdorff Lebesgue topologies on the range space, or for none of them. In particular, subseries convergent series are the same for all Hausdorff Lebesgue topologies on a Riesz space.

     

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。     

仿紧局部可分空间及其映象

探讨仿紧局部可分空间的一些性质,获得了两个可度量化定理,建立了仿紧局部可分空间的各类序列覆盖L-映象的特征。     

The Sequence-covering Compact Images of Paracompact Locally Compact Spaces

Ｉｎｔｈｉｓｐａｐｅｒ,ａｌｌｓｐａｃｅｓａｒｅｒｅｇｕｌａｒａｎｄＴ1,ａｎｄａｌｌｍａｐｐｉｎｇｓａｒｅｃｏｎｔｉｎｕｏｕｓａｎｄｏｎｔｏ .Ｒｅａｄｅｒｓｍａｙｒｅｆｅｒｔｏ [1 ]ｆｏｒｕｎｓｔａｔｅｄｄｅｆｉｎｉｔｉｏｎｓ.　Ｑｕｉｔｅｒｅｃｅｎｔｌｙ ,ｓｏｍｅｃｈａｒａｃｔｅｒｉｚａｔｉｏｎｓｆｏｒｃｅｒｔａｉｎＬ ｉｍａｇｅｓｏｆｐａｒａｃｏｍｐａｃｔｌｏｃａｌｌｙｃｏｍｐａｃｔｓｐａｃｅｓｈａｖｅｂｅｅｎｏｂｔａｉｎｅｄｉｎ [2 ] .Ｓｉｍｉｌａｒｌｙ ,ｗｅｃａｎｅｓｔａｂｌｉｓｈｔｈｅｃｈ…