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4 changes: 4 additions & 0 deletions properties/P000172.md
Original file line number Diff line number Diff line change
Expand Up @@ -19,3 +19,7 @@ Compare with {P80}.

- This property is hereditary.
- $X$ satisfies this property iff its Kolmogorov quotient $\text{Kol}(X)$ does.
- A space that is locally {P172} (every point has a neighborhood with the property)
has the property.
- This property is not preserved by products
(Example: {S78|P172}).
14 changes: 14 additions & 0 deletions theorems/T000774.md
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@@ -0,0 +1,14 @@
---
uid: T000774
if:
P000120: true
then:
P000172: true
---

Let $A\subseteq X$ and $p\in\overline A$.
Since $X$ is {P120}, $p$ has an open neighborhood $U$
that is orderable ({P133}), and hence also {P172}
[(Explore)](https://topology.pi-base.org/spaces?q=LOTS%2B%7ERadial).
Because $p\in\overline{A\cap U}$, and thus $p\in\text{cl}_U(A\cap U)$,
it follows that there is a transfinite sequence of points of $A\cap U$ converging to $p$.