It is well-known that the topological defect of every Fréchet closure space is less than or equal to the first uncountable ordinal number . In the case of Hausdorff Fréchet closure spaces we obtain some general conditions sufficient so that the topological defect is exactly . Some classical and recent results are deduced from our criterion.
The basic concepts of the theory of intuitionistic fuzzy topological spaces have been defined by D. Çoker and co-workers. In this paper, we define new notions of Hausdorffness in the intuitionistic fuzzy sense, and obtain some new properties, in particular on convergence.
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.
This paper investigates necessary and sufficient conditions for a space to have an H-closed extension with countable remainder. For countable spaces we are able to give two characterizations of those spaces admitting an H-closed extension with countable remainder. The general case is more difficult, however, we arrive at a necessary condition — a generalization of Čech completeness, and several sufficient conditions for a space to have an H-closed extension with countable remainder. In particular,...
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...