In this paper -spaces are introduced and studied. They are a common generalization of Lindelöf spaces and -spaces researched by E. Michael. A space is called an -space if, whenever is a closed cover of with compact, then or is Lindelöf. Semi-strong -spaces and strong -spaces are also defined and investigated. It is demonstrated that the three spaces are different and have interesting properties and behaviors.
Nous nous proposons de rendre à Émile Borel le mérite d’avoir considéré le premier un recouvrement d’un segment de droite par une suite infinie d’intervalles et prouvé que l’on peut en extraire un sous-recouvrement fini. L’appellation de théorème de Heine-Borel souvent donnée à ce résultat, en référence à un article de Heine de 1872, conduit à sous-estimer les différences avec le théorème sur la continuité uniforme (dont une première version peut être attribuée à Dirichlet, en 1854) ; cette dénomination...
We prove that if there is a model of set-theory which contains no first countable, locally compact, scattered, countably paracompact space , whose Tychonoff square is a Dowker space, then there is an inner model which contains a measurable cardinal.
Bien que les espaces de Berkovich définis sur un corps trop gros ne soient, en général, pas métrisables, nous montrons que leur topologie reste en grande partie gouvernée par les suites : tout point adhérent à une partie est limite d’une suite de points de cette partie et les parties compactes sont séquentiellement compactes. Notre preuve utilise de façon essentielle l’extension des scalaires et nous en étudions certaines propriétés. Nous montrons qu’un point d’un disque peut être défini sur un...
Arhangel’skii proved that if a first countable Hausdorff space is Lindelöf, then its cardinality is at most . Such a clean upper bound for Lindelöf spaces in the larger class of spaces whose points are has been more elusive. In this paper we continue the agenda started by the second author, [Topology Appl. 63 (1995)], of considering the cardinality problem for spaces satisfying stronger versions of the Lindelöf property. Infinite games and selection principles, especially the Rothberger property,...
We give an example of a compact space X whose iterated continuous function spaces , are Lindelöf, but X is not a Corson compactum. This solves a problem of Gul’ko (Problem 1052 in [11]). We also provide a theorem concerning the Lindelöf property in the function spaces on compact scattered spaces with the th derived set empty, improving some earlier results of Pol [12] in this direction.
Given a locally finite open covering of a normal space X and a Hausdorff topological vector space E, we characterize all continuous functions f: X → E which admit a representation with and a partition of unity subordinate to . As an application, we determine the class of all functions f ∈ C(||) on the underlying space || of a Euclidean complex such that, for each polytope P ∈ , the restriction attains its extrema at vertices of P. Finally, a class of extremal functions on the metric space...
The cardinal functions of pseudocharacter, closed pseudocharacter, and character are used to examine H-closed spaces and to contrast the differences between H-closed and minimal Hausdorff spaces. An H-closed space is produced with the properties that and .