The character of Bing's space

We investigate a canonical method of lowering the character of R.H. Bing's 1952 example G of a normal space which is not collectionwise Hausdorff.We show that adding ℵ_ω Cohen reals to a model of CH produces a model in which there is a normal separable space of weight less than the continuum which is not collectionwise Hausdorff.     

A consistent counterexample in the theory of collectionwise Hausdorff spaces

It is shown to be consistent that there is a normal first countable locally countable space which is not collectionwise Hausdorff and in which there is a closed discrete non-G _δ set which provides the counterexample to collectionwise Hausdorffness. This answers a question of P. Nyikos. Publication 349, partially supported by the BSF.     

Collectionwise Hausdorff versus collectionwise normal with respect to compact sets

Collectionwise normal (CWN) and collectionwise Hausdorff (CWH) spaces have played an increasingly important role in topology since the introduction of these concepts by R.H. Bing in 1951 [3]. It has remained an open and frequently raised question as to whether CWH T₃-spaces are CWN with respect to compact sets. Recently, a counterexample requiring the existence of measurable cardinals and having little additional topological structure was constructed by W.G. Fleissner and the author. In this paper, the author gives a simple example in ZFC of a CWH, first countable, perfect T₃-space that is not CWN with respect to compact, metrizable sets, and, under Martin's Axiom, such an example that is also a Moore space. In addition, the author considers the analogous question for strongly collectionwise Hausdorff (SCWH) T₃-spaces and characterizes the existence of SCWH T₃-spaces that are not CWN with respect to compact sets in set-theoretic and box product formulations. The constructions utilized throughout the paper are of a general nature and several apparently new set-theoretic techniques for interchanging ‘points’ and ‘sets’ are introduced.     

Weak separation axioms and weak covering properties

We identify some remnants of normality and call them rudimentary normality, generalize the concept of submetacompact spaces to that of a weakly subparacompact space and that of a weakly^? subparacompact space, and make a simultaneous generalization of collectionwise normality and screenability with the introduction of what is to be called collectionwise σ-normality. With these weak properties, we show that,1) on weakly subparacompact spaces, countable compactness = compactness, ω₁-compactness = Lindelöfness;2) on weakly subparacompact Hausdorff spaces with rudimentary normality, regularity = normality = countable paracompactness; and3) on weakly subparacompact regular T₁-spaces with rudimentary normality, collectionwise σ-normality = screenability = collectionwise normality = paracompactness.The famous Normal Moore Space Conjecture is thus given an even more striking appearance and Worrell and Wicke?s factorization of paracompactness (over Hausdorff spaces) along with Krajewski?s are combined and strengthened. The methodology extends itself to the factorization of paracompactness on locally compact, locally connected spaces in the manner of Gruenhage and on locally compact spaces in that of Tall, and to the factorization of subparacompactness and metacompactness in the genre of Katuta, Chaber, Junnila and Price and Smith and that of Boone, improving all of them.     

ON A PROJECTION THEOREM FOR MULTIFUNCTIONS

Abstract

Let (T,μ) be a complete measurable space, u a Suslin space and B(u) the Borel σ-algebra of u. The projection theorem, see for example [3], p. 75, states that if the set A belongs to the σ-algebra generated by the class μ x B(U), then its projection P_T(A) belongs to the σ-algebra μ. The aim of this note is to show that the projection theorem fails if (T,μ) is incomplete.     

半素环扩张中心上的模（英文）

设C为半素环R的扩张中心，通过C中的幂等元，我们可以在任意C－模上建立拓扑空间，从拓扑学角度出发，我们证明，殆Hausdorff C- 模为内射模，此外，我们给出殆Hausdorff C-模的一种有趣刻画：若M和N都是殆Hausdorff C-模，则存在一个幂等元e∈C，使得Me可嵌入到Ne中且N（1－e)可嵌入到M（1-e)中。     

The Priestley Separation Axiom for Scattered Spaces

Let R be a quasi-order on a compact Hausdorff topological space X. We prove that if X is scattered, then R satisfies the Priestley separation axiom if and only if R is closed in the product space X×X. Furthermore, if X is not scattered, then we show that there is a quasi-order on X that is closed in X×X but does not satisfy the Priestley separation axiom. As a result, we obtain a new characterization of scattered compact Hausdorff spaces.     

On Prebox Module Topologies

Let R be a complete topological division ring whose topology is determined by a real-valued valuation, and let M be a vector space over R. It is proved that M admits a Hausdorff module topology preceding the box topology in the lattice of all module topologies if and only if the dimension of the vector space M over R is a measurable cardinal.     

On perfectly normal dense subspaces of products

Let M be a separable metric space consisting of more than one point. We construct perfectly normal dense subspaces Z⊂Mc² and (under additional set-theoretic assumption) Y⊂Mc which are not collectionwise Hausdorff.     

A normal screenable nonparacompact space in ZFC

We construct a normal, screenable, nonparacompact space in ZFC. The existence of such a space is also known to imply that there is a normal, screenable space which is not collectionwise normal.

     

Essential extensions of Hausdorff spaces

In the category Haus of Hausdorff spaces the only injectives are the one-point spaces. Even though every Hausdorff spaceX has a maximal essential extension,X fails to have an injective hull, providedX has more than one point. A non-empty Hausdorff space has a proper essential extension if and only ifX is locally H-closed but not H-closed. In this case,X has (up to isomorphism) precisely one proper essential extension: the Obreanu-Porter extension (being simultaneously its maximal essential extension and its minimal H-closed extension). Completely parallel results hold for the categories SReg, Reg, and Tych of semi-regular, regular, and completely regular spaces respectively. In particular, the Alexandroff compactifications of locally compact, non-compact Hausdorff spaces are characterized categorically as the proper essential extensions of non-empty spaces in Tych (resp. Reg).Dedicated to my friend Nico Pumplün on his sixtieth birthday     

TVS-锥度量空间中的统计收敛

本文研究TVS-锥度量空间中的统计收敛以及TVS-锥度量空间的统计完备性.令（X，E，P，d）表示一个TVS-锥度量空间.利用定义在有序Hausdorff拓扑向量空间E上的Minkowski函数ρ，证明了在X上存在一个通常意义下的度量d_ρ，使得X中的序列（x_n）在锥度量d意义下统计收敛到x ∈ X，当且仅当（x_n）在度量d_ρ意义下统计收敛到x.基于此，我们证明了任意一个TVS-锥统计Cauchy序列是几乎处处TVS-锥Cauchy序列，还证明了任意一个TVS-锥统计收敛的序列是几乎处处TVS-锥收敛的.从而，TVS-锥度量空间（X，d）是d-完备的，当且仅当它是d-统计完备的.基于以上结论，通常度量空间中统计收敛的许多性质都可以平行地推广到锥度量空间中统计收敛的情形.     

Linearly ordered covers,normality and paracompactness

It is shown that a regular space is collectionwise normal and countably paracompact if every open cover has an open, order cushioned refinement. A sufficient condition for paracompactness, in terms of certain order locally finite covers, is given, and is applied to the problem of the paracompactness of product spaces.     

Optimal Mutual Location of Compact Sets in Spaces Endowed with Euclidean Invariant Gromov–Hausdorif Metric

Non–empty compact subsets of the Euclidean space located optimally (i.e., the Hausdorff distance between them cannot be decreased) are studied. It is shown that if one of them is a single point, then it is located at the Chebyshev center of the other one. Many other particular cases are considered too. As an application, it is proved that each three–point metric space cari be isometrically embedded into the orbit space of the group of proper motions acting on the compact subsets of the Euclidean space. In addition, it is proved that for each pair of optimally located compact subsets all intermediate compact sets in the sense of Hausdorff metric are also intermediate in the sense of Euclidean Gromov–Hausdorff metric.     

关于纤维一般拓扑的一点注记(英文)

Some characterizations of paracompact maps are given in this note, and some equivalent statements of collectionwise normal maps are discussed. And also we show that if f ： X→Y is a closed collectionwise normal map, and f^-1（y） is a semistratifiable subspace of X for any y ∈ Y, then f is a paracompact map.     

About DK-like spaces and some applications

Let $\text{CSK}$ be the class of all $\text{K}$-scattered spaces having countable ranks. It is shown in this paper that if X is a regular θ-refinable space, then player one has a winning strategy in $\text{G(}\text{DK}\text{,X)}$ if and only if he has one in $\text{G(}\text{CSK}\text{,X)}$. This partly answers Y. Yajima's problem: By topological games, I prove that hereditary disconnectedness, zero-dimensionality and strong zero-dimensionality are equivalent in the realm of non-empty normal compact-scattered weak $\text{θ}$-refinable spaces. A collectionwise normal ultraparacompact-like space is an ultraparacompact space.     

Riesz乘积空间和表示理论

设｛Ｅｉ：ｉ∈Ｉ｝是一族ＡｒｃｈｍｉｄｅａｎＲｉｅｓｚ空间．记Πｉ∈ＩＥｉ为Ｒｉｅｓｚ乘积空间．此文的主要结论是：存在一个完全正则Ｈｏｕｓｄｏｒｆ空间Ｘ使得Πｉ∈ＩＥｉＲｉｅｓｚ同构于Ｃ（Ｘ）的充分必要条件是对每一个ｉ∈Ｉ存在一个完全正则Ｈｏｕｓｄｏｒｆ空间Ｘｉ使得ＥｉＲｉｅｓｚ同构于Ｃ（Ｘｉ）．     

The Bang-Bang,Purification and Convexity Principles in Infinite Dimensions

The authors apply their recent work on the Lyapunov theorem in locally convex Hausdorff spaces to the bang-bang principle for control systems in infinite dimensions. They show that the bang-bang principle holds for every integrably bounded, measurable, weakly compact convex-valued multifunction if and only if the underlying measure space is saturated. They also demonstrate the equivalence of the bang-bang principle to what is termed the purification and convexity principles. Applications to variational problems with integral constraints are indicated.     

Density theorems for generalized Henig proper efficiency

We develop a new, simple technique of proof for density theorems (i.e.,for the sufficient conditions to guarantee that the proper efficient points of a set are dense in the efficient frontier) in an ordered topological vector space. The results are the following: (i) the set of proper efficient points of any compact setQ is dense in the set of efficient points with respect to the original topology of the space whenever the ordering coneK is weakly closed and admits strictly positive functionals; moreover, ifK is not weakly closed, then there exists a compact set for which the density statement fails; (ii) ifQ is weakly compact, then we have only weak density, but ifK has a closed bounded base, then we can assert the density with respect to the original topology, (iii) there exists a similar possibility to assert the strong density for weakly compactQ if additional restrictions are placed onQ instead ofK. These three results are obtained in a unified way as corollaries of the same statement. In this paper, we use the concept of proper efficiency due to Henig. We extend his definition to the setting of a Hausdorff topological vector space.Research of the first author was supported by the Foundation of Fundamental Research of the Republic of Belarus. Authors are grateful to Professor Valentin V. Gorokhovik for suggesting the problem studied in this paper and for numerous fruitful conversations.