Combinatorial aspects of measure and category
Combinatorics of open covers (VII): Groupability
We use Ramseyan partition relations to characterize: ∙ the classical covering property of Hurewicz; ∙ the covering property of Gerlits and Nagy; ∙ the combinatorial cardinal numbers and add(ℳ ). Let X be a -space. In [9] we showed that has countable strong fan tightness as well as the Reznichenko property if, and only if, all finite powers of X have the Gerlits-Nagy covering property. Now we show that the following are equivalent: 1. has countable fan tightness and the Reznichenko property. 2....
Compact sets without converging sequences in the random real model.
Compacta are maximally -resolvable
It is well-known that compacta (i.e. compact Hausdorff spaces) are maximally resolvable, that is every compactum contains many pairwise disjoint dense subsets, where denotes the minimum size of a non-empty open set in . The aim of this note is to prove the following analogous result: Every compactum contains many pairwise disjoint -dense subsets, where denotes the minimum size of a non-empty set in .
Compact-calibres of regular and monotonically normal spaces.
Compact-covering numbers
Compactification and the continuum hypothesis
Compactness of Powers of ω
We characterize exactly the compactness properties of the product of κ copies of the space ω with the discrete topology. The characterization involves uniform ultrafilters, infinitary languages, and the existence of nonstandard elements in elementary extensions. We also have results involving products of possibly uncountable regular cardinals.
Concerning certain minimal cover refineable spaces
Connected LCA groups are sequentially connected
We prove that every connected locally compact Abelian topological group is sequentially connected, i.e., it cannot be the union of two proper disjoint sequentially closed subsets. This fact is then applied to the study of extensions of topological groups. We show, in particular, that if is a connected locally compact Abelian subgroup of a Hausdorff topological group and the quotient space is sequentially connected, then so is .
Constructions of thin-tall Boolean spaces.
This is an expository paper about constructions of locally compact, Hausdorff, scattered spaces whose Cantor-Bendixson height has cardinality greater than their Cantor-Bendixson width.
Continuous functions on products of topological spaces
Continuous images of Lindelöf -groups, -compact groups, and related results
It is shown that there exists a -compact topological group which cannot be represented as a continuous image of a Lindelöf -group, see Example 2.8. This result is based on an inequality for the cardinality of continuous images of Lindelöf -groups (Theorem 2.1). A closely related result is Corollary 4.4: if a space is a continuous image of a Lindelöf -group, then there exists a covering of by dyadic compacta such that . We also show that if a homogeneous compact space is a continuous...
Convergent sequences in
Correction to: Adding a random or a Cohen real: topological consequences and the effect on Martin's axiom
Corrigendum to "Products of pseudoradial spaces".
Countable fan-tightness versus countable tightness
Countable tightness is compared to the stronger notion of countable fan-tightness. In particular, we prove that countable tightness is equivalent to countable fan-tightness in countably compact regular spaces, and that countable fan-tightness is preserved by pseudo-open compact mappings. We also discuss the behaviour of countable tightness and of countable fan-tightness under the product operation.
Countable Hausdorff spaces with countable weight
Covering of a space by nowhere dense sets
Densely continuous forms, pointwise topology and cardinal functions
We consider the space of densely continuous forms introduced by Hammer and McCoy and investigated also by Holá . We show some additional properties of and investigate the subspace of locally bounded real-valued densely continuous forms equipped with the topology of pointwise convergence . The largest part of the paper is devoted to the study of various cardinal functions for , in particular: character, pseudocharacter, weight, density, cellularity, diagonal degree, -weight, -character,...