Absolute Borel sets and function spaces

Marciszewski, Witold; Pelant, Jan

doi:10.1090/S0002-9947-97-01852-7

Absolute Borel sets and function spaces
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by Witold Marciszewski and Jan Pelant PDF

Trans. Amer. Math. Soc. 349 (1997), 3585-3596 Request permission

Abstract:

An internal characterization of metric spaces which are absolute Borel sets of multiplicative classes is given. This characterization uses complete sequences of covers, a notion introduced by Frolík for characterizing Čech-complete spaces. We also show that the absolute Borel class of $X$ is determined by the uniform structure of the space of continuous functions $C_{p}(X)$; however the case of absolute $G_{\delta }$ metric spaces is still open. More precisely, we prove that, for metrizable spaces $X$ and $Y$, if $\Phi : C_{p}(X) \rightarrow C_{p}(Y)$ is a uniformly continuous surjection and $X$ is an absolute Borel set of multiplicative (resp., additive) class $\alpha$, $\alpha >1$, then $Y$ is also an absolute Borel set of the same class. This result is new even if $\Phi$ is a linear homeomorphism, and extends a result of Baars, de Groot, and Pelant which shows that the Čech-completeness of a metric space $X$ is determined by the linear structure of $C_{p}(X)$.

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