Haar spaces and polynomial selections.
The local coincidence of the Hausdorff topology and the uniform convergence topology on the hyperspace consisting of closed graphs of multivalued (or continuous) functions is related to the existence of continuous functions which fail to be uniformly continuous. The problem of the local coincidence of these topologies on is investigated for some classes of spaces: topological groups, zero-dimensional spaces, metric manifolds.
In this paper we introduce and study the concepts of -closed set and -limit (-cluster) points of -nets and -ideals using the notion of almost -compact remoted neighbourhoods in -topological spaces. Then we introduce and study the concept of -continuous mappings. Several characterizations based on -closed sets and the -convergence theory of -nets and -ideals are presented for -continuous mappings.
The notion of a Hausdorff function is generalized to the concept of H-closed function and the concept of an H-closed extension of a Hausdorff function is developed. Each Hausdorff function is shown to have an H-closed extension.
A classical theorem of Hurewicz characterizes spaces with the Hurewicz covering property as those having bounded continuous images in the Baire space. We give a similar characterization for spaces which have the Hurewicz property hereditarily. We proceed to consider the class of Arhangel’skii spaces, for which every sheaf at a point can be amalgamated in a natural way. Let denote the space of continuous real-valued functions on with the topology of pointwise convergence. Our main result...
Several classes of hereditarily normal spaces are characterized in terms of extending upper semi-continuous compact-valued mappings. The case of controlled extensions is considered as well. Applications are obtained for real-valued semi-continuous functions.