English

Hyperspaces with a countable character of closed subsets

General Topology 2022-11-11 v2

Abstract

For a regular space XX, the hyperspace (CL(X),τF)(CL(X), \tau_{F}) (resp., (CL(X),τV)(CL(X), \tau_{V})) is the space of all nonempty closed subsets of XX with the Fell topology (resp., Vietoris topology). In this paper, we give the characterization of the space XX such that the hyperspace (CL(X),τF)(CL(X), \tau_{F}) (resp., (CL(X),τV)(CL(X), \tau_{V})) with a countable character of closed subsets. We mainly prove that (CL(X),τF)(CL(X), \tau_F) has a countable character on each closed subset if and only if XX is compact metrizable, and (CL(X),τF)(CL(X), \tau_F) has a countable character on each compact subset if and only if XX is locally compact and separable metrizable. Moreover, we prove that (K(X),τV)(\mathcal{K}(X), \tau_V) have the compact-GδG_\delta property if and only if XX have the compact-GδG_\delta property and every compact subset of XX is metrizable.

Keywords

Cite

@article{arxiv.2206.13026,
  title  = {Hyperspaces with a countable character of closed subsets},
  author = {Chuan Liu and Fucai Lin},
  journal= {arXiv preprint arXiv:2206.13026},
  year   = {2022}
}

Comments

14 pages

R2 v1 2026-06-24T12:04:41.522Z