English

Covering versus partitioning with the Cantor space

General Topology 2021-09-09 v2

Abstract

What topological spaces can be partitioned into copies of the Cantor space 2ω2^\omega? An obvious necessary condition is that a space can be partitioned into copies of 2ω2^\omega only if it can be covered with copies of 2ω2^\omega. We prove three theorems concerning when this necessary condition is also sufficient. If XX is a metrizable space and Xc+ω|X| \leq \mathfrak{c}^{+\omega} (the least limit cardinal > ⁣c>\!\mathfrak{c}), then XX can be partitioned into copies of 2ω2^\omega if and only if XX can be covered with copies of 2ω2^\omega. To show this cardinality bound is sharp, we construct a metrizable space of size c+(ω+1)\mathfrak{c}^{+(\omega+1)} that can be covered with copies of 2ω2^\omega, but not partitioned into copies of 2ω2^\omega. Similarly, if XX is first countable and Xc|X| \leq \mathfrak{c}, then XX can be partitioned into copies of 2ω2^\omega if and only if XX can be covered with copies of 2ω2^\omega. On the other hand, there is a first countable space of size c+\mathfrak{c}^+ that can be covered with copies of 2ω2^\omega, but not partitioned into copies of 2ω2^\omega. Finally, we show that a completely metrizable space can be partitioned into copies of 2ω2^\omega if and only if it can be covered with copies of 2ω2^\omega if and only if it has no isolated points.

Keywords

Cite

@article{arxiv.2103.05725,
  title  = {Covering versus partitioning with the Cantor space},
  author = {Will Brian},
  journal= {arXiv preprint arXiv:2103.05725},
  year   = {2021}
}
R2 v1 2026-06-23T23:56:17.398Z