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10 changes: 10 additions & 0 deletions spaces/S000019/properties/P000099.md
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---
space: S000019
property: P000099
value: false
refs:
- doi: 10.1007/978-1-4612-6290-9_6
name: Counterexamples in Topology
---

The sequence $(n)_{n\in\omega}$ is eventually outside of every compact subset of $\mathbb R$, that is, inside of every nonempty open set in $X$. So it converges to every point of $X$.
10 changes: 0 additions & 10 deletions spaces/S000024/properties/P000003.md

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10 changes: 10 additions & 0 deletions spaces/S000024/properties/P000099.md
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---
space: S000024
property: P000099
value: false
refs:
- doi: 10.1007/978-1-4612-6290-9_6
name: Counterexamples in Topology
---

An infinite sequence of distinct points of $\mathbb R$ converges to both $\infty_1$ and $\infty_2$.
2 changes: 1 addition & 1 deletion spaces/S000097/README.md
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Expand Up @@ -7,7 +7,7 @@ refs:
- doi: 10.1007/978-1-4612-6290-9
name: Counterexamples in Topology
---
Let $X$ be the set of all lattice points $(i,j) \in \omega^2$ along with two extra points $x$ and $y$. Let each $(i,j)$ be open. Neighborhoods of $x$ have the form $X \setminus A$ where $A$ is any set of lattice points with at most finitely many points on each row. Neighborhoods of $y$ have the form $X \setminus B$ where $B$ is any set of lattice points selected from at most finitely many rows.
Let $X$ be the set of all lattice points $(i,j) \in \omega^2$ together with two extra points $x$ and $y$. Let each $(i,j)$ be open. Basic neighborhoods of $x$ have the form $X \setminus (A\cup\{y\})$ where $A$ is any set of lattice points with at most finitely many points on each row. Basic neighborhoods of $y$ have the form $X \setminus (B\cup\{x\})$ where $B$ is any set of lattice points selected from at most finitely many rows.

Defined as counterexample #99 ("Maximal Compact Topology")
in {{doi:10.1007/978-1-4612-6290-9}}.
10 changes: 10 additions & 0 deletions spaces/S000097/properties/P000100.md
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---
space: S000097
property: P000100
value: true
refs:
- doi: 10.1007/978-1-4612-6290-9_6
name: Counterexamples in Topology
---

See item #3 for space #99 in {{doi:10.1007/978-1-4612-6290-9_6}}.
2 changes: 1 addition & 1 deletion spaces/S000165/README.md
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name: Answer to ""All retracts are closed" and "all compacts are closed""
---

The one-point compactification of {S23}, see {{mo:435257}}.
The one-point compactification $X$ of {S23}. See [this answer](https://mathoverflow.net/a/435257) to {{mo:435257}}.
11 changes: 0 additions & 11 deletions spaces/S000165/properties/P000003.md

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12 changes: 12 additions & 0 deletions spaces/S000165/properties/P000143.md
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---
space: S000165
property: P000143
value: false
refs:
- mo: 435257
name: Answer to ""All retracts are closed" and "all compacts are closed""
---

Let $0$ be the non-isolated point of the Arens-Fort space. The subspace $A=X\setminus\{0\}$ is homeomorphic to the one-point compactification of a discrete space (i.e., {S20}), which is compact and Hausdorff. But $A$ is not closed in $X$.

See [this answer](https://mathoverflow.net/a/435257) to {{mo:435257}}.