Displaying 121 – 140 of 163

Showing per page

Topological spaces compact with respect to a set of filters

Paolo Lipparini (2014)

Open Mathematics

If is a family of filters over some set I, a topological space X is sequencewise -compact if for every I-indexed sequence of elements of X there is such that the sequence has an F-limit point. Countable compactness, sequential compactness, initial κ-compactness, [λ; µ]-compactness, the Menger and Rothberger properties can all be expressed in terms of sequencewise -compactness for appropriate choices of . We show that sequencewise -compactness is preserved under taking products if and only if there...

Topologically maximal convergences, accessibility, and covering maps

Szymon Dolecki, Michel Pillot (1998)

Mathematica Bohemica

Topologically maximal pretopologies, paratopologies and pseudotopologies are characterized in terms of various accessibility properties. Thanks to recent convergence-theoretic descriptions of miscellaneous quotient maps (in terms of topological, pretopological, paratopological and pseudotopological projections), the quotient characterizations of accessibility (in particular, those of G. T. Whyburn and F. Siwiec) are shown to be instances of a single general theorem. Convergence-theoretic characterizations...

Topologies generated by ideals

Carlos Uzcátegui (2006)

Commentationes Mathematicae Universitatis Carolinae

A topological space X is said to be generated by an ideal if for all A X and all x A ¯ there is E A in such that x E ¯ , and is said to be weakly generated by if whenever a subset A of X contains E ¯ for every E A with E , then A itself is closed. An important class of examples are the so called weakly discretely generated spaces (which include sequential, scattered and compact Hausdorff spaces). Another paradigmatic example is the class of Alexandroff spaces which corresponds to spaces generated by finite sets....

Totally bounded frame quasi-uniformities

Peter Fletcher, Worthen N. Hunsaker, William F. Lindgren (1993)

Commentationes Mathematicae Universitatis Carolinae

This paper considers totally bounded quasi-uniformities and quasi-proximities for frames and shows that for a given quasi-proximity on a frame L there is a totally bounded quasi-uniformity on L that is the coarsest quasi-uniformity, and the only totally bounded quasi-uniformity, that determines . The constructions due to B. Banaschewski and A. Pultr of the Cauchy spectrum ψ L and the compactification L of a uniform frame ( L , 𝐔 ) are meaningful for quasi-uniform frames. If 𝐔 is a totally bounded quasi-uniformity...

Totally Brown subsets of the Golomb space and the Kirch space

José del Carmen Alberto-Domínguez, Gerardo Acosta, Gerardo Delgadillo-Piñón (2022)

Commentationes Mathematicae Universitatis Carolinae

A topological space X is totally Brown if for each n { 1 } and every nonempty open subsets U 1 , U 2 , ... , U n of X we have cl X ( U 1 ) cl X ( U 2 ) cl X ( U n ) . Totally Brown spaces are connected. In this paper we consider the Golomb topology τ G on the set of natural numbers, as well as the Kirch topology τ K on . Then we examine subsets of these spaces which are totally Brown. Among other results, we characterize the arithmetic progressions which are either totally Brown or totally separated in ( , τ G ) . We also show that ( , τ G ) and ( , τ K ) are aposyndetic. Our results...

Currently displaying 121 – 140 of 163