English

Distinguishing perfect set properties in separable metrizable spaces

Logic 2014-08-25 v2 General Topology

Abstract

All spaces are assumed to be separable and metrizable. Our main result is that the statement "For every space XX, every closed subset of XX has the perfect set property if and only if every analytic subset of XX has the perfect set property" is equivalent to b>ω1\mathfrak{b}>\omega_1 (hence, in particular, it is independent of ZFC\mathsf{ZFC}). This, together with a theorem of Solecki and an example of Miller, will allow us to determine the status of the statement "For every space XX, if every Γ\mathbf{\Gamma} subset of XX has the perfect set property then every Γ\mathbf{\Gamma}' subset of XX has the perfect set property" as Γ,Γ\mathbf{\Gamma},\mathbf{\Gamma}' range over all pointclasses of complexity at most analytic or coanalytic. Along the way, we define and investigate a property of independent interest. We will say that a subset WW of 2ω2^\omega has the Grinzing property if it is uncountable and for every uncountable YWY\subseteq W there exists an uncountable collection consisting of uncountable subsets of YY with pairwise disjoint closures in 2ω2^\omega. The following theorems hold. (1) There exists a subset of 2ω2^\omega with the Grinzing property. (2) Assume MA+¬CH\mathsf{MA}+\neg\mathsf{CH}. Then 2ω2^\omega has the Grinzing property. (3) Assume CH\mathsf{CH}. Then 2ω2^\omega does not have the Grinzing property. The first result was obtained by Miller using a theorem of Todor\v{c}evi\'c, and is needed in the proof of our main result.

Keywords

Cite

@article{arxiv.1405.0191,
  title  = {Distinguishing perfect set properties in separable metrizable spaces},
  author = {Andrea Medini},
  journal= {arXiv preprint arXiv:1405.0191},
  year   = {2014}
}

Comments

14 pages

R2 v1 2026-06-22T04:04:03.901Z