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3 changes: 0 additions & 3 deletions spaces/S000136/properties/P000019.md
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space: S000136
property: P000019
value: false
refs:
- zb: "0386.54001"
name: Counterexamples in Topology
---

Closed subspaces of {P19} spaces are {P19}, but the closed subspace {S137} of this space is not {P19}.
9 changes: 9 additions & 0 deletions spaces/S000136/properties/P000051.md
Comment thread
felixpernegger marked this conversation as resolved.
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---
space: S000136
property: P000051
value: true
---

For $r \in \mathbb{R}$ consider $U_r := \{f \in 2^\mathbb{R} \to 2\mid f(\{r\})=1\} \subseteq X$. Note that $U_r$ is open in the product topology and therefore open in $X$. Furthermore $U_r \cap M = \{x_r\}$, so $x_r$ is isolated in $M$ and thus $M$ is discrete as a subspace.

Hence, if $A \subseteq X$ contains no elements of $X \setminus M$ we are done, otherwise $A$ already contains an isolated point by definition.
10 changes: 0 additions & 10 deletions spaces/S000136/properties/P000139.md

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7 changes: 7 additions & 0 deletions spaces/S000137/properties/P000051.md
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---
space: S000137
property: P000051
value: true
---

$X$ is a subspace of {S136} and {S136|P51}.
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