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Some topological properties of ω -covering sets

Andrzej Nowik (2000)

Czechoslovak Mathematical Journal

We prove the following theorems: There exists an ω -covering with the property s 0 . Under c o v ( 𝒩 ) = there exists X such that B o r [ B X is not an ω -covering or X B is not an ω -covering]. Also we characterize the property of being an ω -covering.

Some variations on the partition property for normal ultrafilters on Pkl

Julius Barbanel (1993)

Fundamenta Mathematicae

Suppose κ is a supercompact cardinal and λ≥κ. In [3], we studied the relationship between the weak partition property and the partition property for normal ultrafilters on P κ λ . In this paper we study a hierarchy of properties intermediate between the weak partition property and the partition property. Given appropriate large cardinal assumptions, we show that these properties are not all equivalent.

Spaces not distinguishing convergences

Miroslav Repický (2000)

Commentationes Mathematicae Universitatis Carolinae

In the present paper we introduce a convergence condition ( Σ ' ) and continue the study of “not distinguish” for various kinds of convergence of sequences of real functions on a topological space started in [2] and [3]. We compute cardinal invariants associated with introduced properties of spaces.

Spectra of uniformity

Yair Hayut, Asaf Karagila (2019)

Commentationes Mathematicae Universitatis Carolinae

We study some limitations and possible occurrences of uniform ultrafilters on ordinals without the axiom of choice. We prove an Easton-like theorem about the possible spectrum of successors of regular cardinals which carry uniform ultrafilters; we also show that this spectrum is not necessarily closed.

Splitting stationary sets in κ λ for λ with small cofinality

Toshimichi Usuba (2009)

Fundamenta Mathematicae

For a regular uncountable cardinal κ and a cardinal λ with cf(λ) < κ < λ, we investigate the consistency strength of the existence of a stationary set in κ λ which cannot be split into λ⁺ many pairwise disjoint stationary subsets. To do this, we introduce a new notion for ideals, which is a variation of normality of ideals. We also prove that there is a stationary set S in κ λ such that every stationary subset of S can be split into λ⁺ many pairwise disjoint stationary subsets.

Splitting ω -covers

Winfried Just, Andreas Tanner (1997)

Commentationes Mathematicae Universitatis Carolinae

The authors give a ZFC example for a space with Split ( Ω , Ω ) but not Split ( Λ , Λ ) .

Stable families of analytic sets

Pandelis Dodos (2003)

Colloquium Mathematicae

We give a different proof of the well-known fact that any uncountable family of analytic subsets of a Polish space with the point-finite intersection property must contain a subfamily whose union is not analytic. Our approach is based on the Kunen-Martin theorem.

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