There are arbitrarily large uniquely homogeneous spaces (Q2215686)
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| Language | Label | Description | Also known as |
|---|---|---|---|
| English | There are arbitrarily large uniquely homogeneous spaces |
scientific article |
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There are arbitrarily large uniquely homogeneous spaces (English)
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14 December 2020
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A space \(X\) is uniquely homogeneous if for every pair \((x,y)\) of points of \(X\) there exists a unique homeomorphism \(h:X\longrightarrow X\) such that \(h(x)=y\). The article under review contains a nice historical introduction to the topic, so here we will only mention that the first non-trivial (that is, containing more than two elements) examples of such spaces were given in [\textit{J. van Mill}, Trans. Am. Math. Soc. 280, 491--498 (1983; Zbl 0573.22001); Fundam. Math. 122, 255--264 (1984; Zbl 0562.54042)]. Furthermore, it is a result of \textit{A. V. Arhangel'skii} and \textit{J. van Mill} [J. Math. Soc. Japan 64, No. 3, 903--926 (2012; Zbl 1257.54020)] that every non-trivial uniquely homogeneous space is connected. For every integer \(n\geq 2\), the author gives a \(\mathsf{ZFC}\) example of a uniquely homogeneous Bernstein subspace \(X\) of \(\mathbb{R}^n\). It follows that \(X\) is also locally connected and has dimension \(n-1\) (see [\textit{I. Banakh} et al., Carpathian Math. Publ. 9, No. 1, 3--5 (2017; Zbl 1372.22001)]). The main idea of the proof is a clever modification of a construction of \textit{J. E. Keesling} and \textit{D. C. Wilson} [Topology Appl. 22, 183--190 (1986, Zbl 0586.57019)]. The same method also yields, for every infinite cardinal \(\kappa\), a dense uniquely homogeneous subspace of \(\mathbb{R}^I\), where \(I=2^\kappa\). In particular, the result stated in the title follows. These spaces are also locally connected.
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homogeneous
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uniquely homogeneous
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