3
$\begingroup$

  1. Is the Stone–Čech compactification of a dense $G_\delta$-set $X \subset\beta N \setminus N$ homeomorphic to $\beta N \setminus N$? Here, $\beta N \setminus N$ is the complement of $N$ in the Stone–Čech compactification of $N$.

  2. For every dense $G_\delta$ subset $A \subset$ $\beta N \setminus N$, is it true that there is a dense subset $B\subset A $ such that $\beta B=\beta N \setminus N$?

Improve this question
$\endgroup$
2
  • $\begingroup$ For this problem, do you mean that $\beta N\setminus N$ $\textit{is}$ the Stone-Cech compactification of a dense $G_{\delta}$-set $X$ (i.e. $X$ is $C^{*}$-embedded in $\beta N\setminus N$) or simply that $\beta X$ and $\beta N\setminus N$ are homeomorphic as you have said? $\endgroup$
    – Joseph Van Name
    Commented Jan 31, 2014 at 17:04
  • $\begingroup$ @JosephVanName: that´s a good point. I should point out however that in the Corollary 1.5.4 mentioned in my answer it is actually proved that $\omega^*\setminus\{x\}$ can not be $C^*$-embedded in $\beta N$ and therefore cannot be homeomorphic to $\omega^*$. $\endgroup$
    – Ramiro de la Vega
    Commented Jan 31, 2014 at 18:32

1 Answer 1

Reset to default
7
$\begingroup$

If you consider only complements of points, which are particular dense $G_\delta$-sets, the answer is independent of $ZFC$. The following results can be found in van Mill´s article in the Handbook of Set-Theoretic Topology:

Corollary 1.5.4: $(CH)$ If $x \in \omega^*$ then $\omega^* \setminus \{x\}$ is not $C^*$-embedded in $\omega^*$.

and

Corollary 2.5.3: It is consistent that for some $x \in \omega^*$ we have that $\beta (\omega^* \setminus \{x\})=\omega^*$.

I don´t know if it is possible to prove in $ZFC$ that there is a dense $G_\delta$-subset of $\omega^*$ which is not $C^*$-embedded in $\omega^*$.

Improve this answer
$\endgroup$

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .