-spaces and images of separable metric spaces.
For every topological property , we define the class of -approximable spaces which consists of spaces X having a countable closed cover such that the “section” has the property for each . It is shown that every -approximable compact space has , if is one of the following properties: countable tightness, -scatteredness with respect to character, -closedness, sequentiality (the last holds under MA or ). Metrizable-approximable spaces are studied: every compact space in this class has...
In the present paper, we introduce and study the concept of -closed sets in biclosure spaces and investigate its behavior. We also introduce and study the concept of -continuous maps.
We show that the uniform compactification of a uniform space (X,𝓤) can be considered as a space of filters on X. We apply these filters to study the ℒ𝓤𝓒-compactification of a topological group.
Recently Popa and Noiri [10] established some new characterizations and basic properties of -continuous multifunctions. In this paper, we improve some of their results and examine further properties of -continuous and -irresolute multifunctions. We also make corrections to some theorems of Neubrunn [7].
We use the -Ponomarev-system , where is a locally separable metric space, to give a consistent method to construct a -mapping (compact mapping) with covering-properties from a locally separable metric space onto a space . As applications of these results, we systematically get characterizations of certain -images (compact images) of locally separable metric spaces.
We prove a separable reduction theorem for -porosity of Suslin sets. In particular, if is a Suslin subset in a Banach space , then each separable subspace of can be enlarged to a separable subspace such that is -porous in if and only if is -porous in . Such a result is proved for several types of -porosity. The proof is done using the method of elementary submodels, hence the results can be combined with other separable reduction theorems. As an application we extend a theorem...