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Characterizing Complete Erdős Space
Published online by Cambridge University Press: 20 November 2018
Abstract
The space now known as complete Erdős space${{\mathfrak{E}}_{\text{c}}}$ was introduced by Paul Erdős in 1940 as the closed subspace of the Hilbert space
${{\ell }^{2}}$ consisting of all vectors such that every coordinate is in the convergent sequence
$\left\{ 0 \right\}\cup \left\{ 1/n:n\in \mathbb{N}\ \right\}$. In a solution to a problem posed by Lex
$G$. Oversteegen we present simple and useful topological characterizations of
${{\mathfrak{E}}_{\text{c}}}$. As an application we determine the class of factors of
${{\mathfrak{E}}_{\text{c}}}$. In another application we determine precisely which of the spaces that can be constructed in the Banach spaces
${{\ell }^{p}}$ according to the ‘Erdős method’ are homeomorphic to
${{\mathfrak{E}}_{\text{c}}}$. A novel application states that if
$I$ is a Polishable
${{F}_{\sigma }}$-ideal on
$\omega $, then
$I$ with the Polish topology is homeomorphic to either
$\mathbb{Z}$, the Cantor set
${{2}^{\omega }},\,\mathbb{Z}\,\times \,{{2}^{\omega }}$, or
${{\mathfrak{E}}_{\text{c}}}$. This last result answers a question that was asked by Stevo Todorčević.
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- Research Article
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- Copyright © Canadian Mathematical Society 2009