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| Format: | Preprint |
| Publié: |
2024
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| Accès en ligne: | https://arxiv.org/abs/2401.14384 |
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| _version_ | 1866911094926213120 |
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| author | Gutev, Valentin |
| author_facet | Gutev, Valentin |
| contents | If $f$ is a continuous selection for the Vietoris hyperspace $\mathscr{F}(X)$ of the nonempty closed subsets of a space $X$, then the point $f(X)\in X$ is not as arbitrary as it might seem at first glance. In this paper, we will characterise these points by local properties at them. Briefly, we will show that $p=f(X)$ is a strong butterfly point precisely when it has a countable clopen base in $\overline{U}$ for some open set $U\subset X\setminus\{p\}$ with $\overline{U}=U\cup\{p\}$. Moreover, the same is valid when $X$ is totally disconnected at $p=f(X)$ and $p$ is only assumed to be a butterfly point. This gives the complete affirmative solution to a question raised previously by the author. Finally, when $p=f(X)$ lacks the above local base-like property, we will show that $\mathscr{F}(X)$ has a continuous selection $h$ with the stronger property that $h(S)=p$ for every closed $S\subset X$ with $p\in S$. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2401_14384 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Butterfly Points and Hyperspace Selections Gutev, Valentin General Topology 54A20, 54B20, 54C65 If $f$ is a continuous selection for the Vietoris hyperspace $\mathscr{F}(X)$ of the nonempty closed subsets of a space $X$, then the point $f(X)\in X$ is not as arbitrary as it might seem at first glance. In this paper, we will characterise these points by local properties at them. Briefly, we will show that $p=f(X)$ is a strong butterfly point precisely when it has a countable clopen base in $\overline{U}$ for some open set $U\subset X\setminus\{p\}$ with $\overline{U}=U\cup\{p\}$. Moreover, the same is valid when $X$ is totally disconnected at $p=f(X)$ and $p$ is only assumed to be a butterfly point. This gives the complete affirmative solution to a question raised previously by the author. Finally, when $p=f(X)$ lacks the above local base-like property, we will show that $\mathscr{F}(X)$ has a continuous selection $h$ with the stronger property that $h(S)=p$ for every closed $S\subset X$ with $p\in S$. |
| title | Butterfly Points and Hyperspace Selections |
| topic | General Topology 54A20, 54B20, 54C65 |
| url | https://arxiv.org/abs/2401.14384 |