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Space Suggestion: Non-normal subspace of beta N and Dow plank #1230

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Moniker1998 opened this issue Feb 9, 2025 · 2 comments
Open

Space Suggestion: Non-normal subspace of beta N and Dow plank #1230

Moniker1998 opened this issue Feb 9, 2025 · 2 comments
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@Moniker1998
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Space Suggestion

First example of non-normal extremally disconnected space is $\mathbb{N}\cup \{p_A: A\in\mathcal{A}\}$, $\mathcal{A}$ maximal almost disjoint family, $p_A\in \text{cl}_{\beta\mathbb{N}} A\setminus\mathbb{N}$. It's the space witnessing that $\beta\mathbb{N}$ is not $T_5$ so name probably should reflect that.

Second example of non-normal $P$-space is $X^2\setminus \{(\omega_2, \omega_2)\}$ where $X = \omega_2+1$ has topology letting $U\subseteq X$ be open iff its a $G_\delta$-set in the order topology. I would like to call it Dow plank since it's a space that appears in the article On F-spaces and F'-spaces by Dow, clearly analogous to something like the Tychonoff plank.

Rationale

First example is in Engelking, second I mentioned the article already.

Relationship to other spaces and properties

They provide searches for non-normal extremally disconnected and non-normal P-spaces.

@yhx-12243
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Is the first example the same as #1201?

@Moniker1998
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@yhx-12243 oh sorry I forgot that existed, since it was sitting there for so long.
Not quite, but it's similar. And also showing that $\beta\mathbb{N}$ is non-normal. Moreover it's more specific

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