English

Covering versus partitioning with Polish spaces

Logic 2021-01-26 v1 General Topology

Abstract

Given a completely metrizable space XX, let par(X)\mathfrak{par}(X) denote the smallest possible size of a partition of XX into Polish spaces, and cov(X)\mathfrak{cov}(X) the smallest possible size of a covering of XX with Polish spaces. Observe that cov(X)par(X)\mathfrak{cov}(X) \leq \mathfrak{par}(X) for every XX, because every partition of XX is also a covering. We prove it is consistent relative to a huge cardinal that the strict inequality cov(X)<par(X)\mathfrak{cov}(X) < \mathfrak{par}(X) can hold for some completely metrizable space XX. We also prove that using large cardinals is necessary for obtaining this strict inequality, because if cov(X)<par(X)\mathfrak{cov}(X) < \mathfrak{par}(X) for any completely metrizable XX, then 00^\dagger exists.

Keywords

Cite

@article{arxiv.2101.10088,
  title  = {Covering versus partitioning with Polish spaces},
  author = {Will Brian},
  journal= {arXiv preprint arXiv:2101.10088},
  year   = {2021}
}
R2 v1 2026-06-23T22:29:35.579Z