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On π -caliber and an application of Prikry’s partial order

Andrzej Szymański — 2011

Commentationes Mathematicae Universitatis Carolinae

We study the concept of π -caliber as an alternative to the well known concept of caliber. π -caliber and caliber values coincide for regular cardinals greater than or equal to the Souslin number of a space. Unlike caliber, π -caliber may take on values below the Souslin number of a space. Under Martin’s axiom, 2 ω is a π -caliber of * . Prikry’s poset is used to settle a problem by Fedeli regarding possible values of very weak caliber.

Measurable cardinals and category bases

Andrzej Szymański — 1991

Commentationes Mathematicae Universitatis Carolinae

We show that the existence of a non-trivial category base on a set of regular cardinality with each subset being Baire is equiconsistent to the existence of a measurable cardinal.

Short proofs of two theorems in topology

Mohammad IsmailAndrzej Szymański — 1993

Commentationes Mathematicae Universitatis Carolinae

We present short and elementary proofs of the following two known theorems in General Topology: (i) [H. Wicke and J. Worrell] A T 1 weakly δ θ -refinable countably compact space is compact. (ii) [A. Ostaszewski] A compact Hausdorff space which is a countable union of metrizable spaces is sequential.

Eberlein spaces of finite metrizability number

István JuhászZoltán SzentmiklóssyAndrzej Szymański — 2007

Commentationes Mathematicae Universitatis Carolinae

Yakovlev [, Comment. Math. Univ. Carolin. (1980), 263–283] showed that any Eberlein compactum is hereditarily σ -metacompact. We show that this property actually characterizes Eberlein compacta among compact spaces of finite metrizability number. Uniformly Eberlein compacta and Corson compacta of finite metrizability number can be characterized in an analogous way.

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