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A Universal Quasi-Polish Space
Abstract
In this paper, we first construct a universal quasi-Polish space Y with the property that every quasi-Polish space is homeomorphic to a closed subspace of Y. This gives a hyperspace F(Y) of all quasi-Polish spaces which is itself a quasi-Polish space. We then prove that the collection of all Polish closed subspaces of Y forms a coanalytic, non-Borel subset of F(Y). In particular, this collection is Π11-complete.
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BibTeX
@misc{gao2026universal,
title = {{A Universal Quasi-Polish Space}},
author = {Su Gao and Qingguo Li and Hualin Miao},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.11417},
eprint = {2610.11417},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.11417},
}
RIS
TY - UNPB
TI - A Universal Quasi-Polish Space
AU - Su Gao
AU - Qingguo Li
AU - Hualin Miao
PY - 2026
DA - 2026/10/08
PB - arXiv
DO - 10.48550/arxiv.2610.11417
UR - https://arxiv.org/abs/2610.11417
AB - In this paper, we first construct a universal quasi-Polish space Y with the property that every quasi-Polish space is homeomorphic to a closed subspace of Y. This gives a hyperspace F(Y) of all quasi-Polish spaces which is itself a quasi-Polish space. We then prove that the collection of all Polish closed subspaces of Y forms a coanalytic, non-Borel subset of F(Y). In particular, this collection is Π11-complete.
ER -