Saturday, 4 October 2014

gn.general topology - A question about totally disconnected point sets.

Let $E_c$ be the complete Erdös space (Erdös, Annals of Math vol 41 1940), defined as the subspace of $ell^2(mathbb{N})$ where all coordinates are irrationals. It is polish (separable and completely metrizable) and totally disconnected, but admits a "connectification" namely a (still polish) topology on $E_ccup{p}$ that makes it connected (and of course induces the one on $E_c$). The crucial point is the fact that any nonempty closed and open subset of $E_c$ is unbounded. Then, as in Bill Johnson's answer $E_c$ is the union of the closed and totally disconnected subspaces $overline{B}(0,n)cup{p}$, $ngeq 1$. It remains to remark that, like any polish space, $E_ccup{p}$ embeds as a closed subset of $H$ (as remarked in Gerald Edgar's answer).

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