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show long circle is T5 but not perfectly normal #1104

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Dec 31, 2024
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8 changes: 8 additions & 0 deletions properties/P000015.md
Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,8 @@ refs:
name: General Topology (Engelking, 1989)
- mathse: 72138
name: Why are these two definitions of a perfectly normal space equivalent?
- mathse: 1840621
name: Answer to "Perfectly Normal is hereditary"
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---

A space $X$ for which, for any disjoint closed sets $A$ and $B$, there is a
Expand All @@ -20,3 +22,9 @@ in Theorem 1.5.19 of {{zb:0684.54001}} (under the assumption of a {P2} space, bu
equally valid without this assumption). See also {{mathse:72138}}.

Defined on page 16 of {{doi:10.1007/978-1-4612-6290-9}} (as perfectly \(T_4\)).

----

#### Meta-properties

- This property is hereditary (see {{mathse:1840621}}).
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9 changes: 8 additions & 1 deletion properties/P000067.md
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Expand Up @@ -12,6 +12,13 @@ refs:
name: Normal space on Wikipedia
---

A space that is both {P2} and {P15}. Equivalently, a space that is both {P1} and {P15}.
A space that is both {P2} and {P15}.
Equivalently, a space that is both {P1} and {P15}.

Defined on page 16 of {{doi:10.1007/978-1-4612-6290-9}} as "perfectly normal".

----

#### Meta-properties

- This property is hereditary since {P2} and {P15} are.
6 changes: 6 additions & 0 deletions properties/P000081.md
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Expand Up @@ -7,3 +7,9 @@ refs:
---

For each $A\subseteq X$ and each $p\in \overline A$ there is a countable subset $D\subseteq A$ such that $p\in \overline D$.

----

#### Meta-properties

- This property is hereditary.
10 changes: 0 additions & 10 deletions spaces/S000196/properties/P000003.md

This file was deleted.

7 changes: 7 additions & 0 deletions spaces/S000196/properties/P000008.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,7 @@
---
space: S000196
property: P000008
value: true
---

Every proper subspace is {P154} and thus {P7}.
8 changes: 8 additions & 0 deletions spaces/S000196/properties/P000081.md
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@@ -0,0 +1,8 @@
---
space: S000196
property: P000081
value: false
---

This space contains a copy of {S36}, and
{S36|P81}.
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