A compact convex set not convexly totally bounded (Q2770173)
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scientific article; zbMATH DE number 1702902
| Language | Label | Description | Also known as |
|---|---|---|---|
| English | A compact convex set not convexly totally bounded |
scientific article; zbMATH DE number 1702902 |
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12 May 2002
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convex set
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convexly totally bounded set
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needle point
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Ribe space
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Schauder's fixed point theorem
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0.8767344
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0.86051255
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0.85492057
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0.8517476
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0.8500088
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0.84908354
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A compact convex set not convexly totally bounded (English)
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In connection with Schauder's conjecture ``Does every compact convex set in an arbitrary Hausdorff topological linear space have the fixed point property?'', \textit{A. Idzik} [ibid. 35, 461-464 (1987; Zbl 0663.47036)] asked whether each compact convex set \(K\) in a Hausdorff topological linear space is convexly totally bounded, i.e., for each neighbourhood \(U\) of zero there are \(x_1,\dotsc,x_n\in K\) and convex subsets \(C_1,\dots,C_n\subset U\) such that \(K\subset\bigcup_{i=1}^n(x_i+C_i)\). A positive answer to Idzik's question would have solved Schauder's problem. The present author gives a simple example of a compact convex set in Ribe space [cf. \textit{M. Ribe}, Proc. Am. Math. Soc. 237, 351-355 (1979; Zbl 0397.46002)] which is not convexly totally bounded. \{In the meantime, \textit{R. Cauty} [Fund. Math. 170, 231-246 (2001; Zbl 0983.54045)] has solved Schauder's problem in the positive\}.
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