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multiple more theorems
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danflapjax authored Oct 14, 2024
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1 change: 0 additions & 1 deletion theorems/T000552.md
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Expand Up @@ -8,7 +8,6 @@ if:
then:
P000129: true
---

If a {P196} space is {P16}, then it must have a second largest open set
(otherwise, $\mathcal T_X\setminus\{X\}$ would be totally ordered with no upper bound and therefore an open cover with no finite subcover).
To be {P86}, no points can lie in this second-largest set, so the space is {P129}.
11 changes: 3 additions & 8 deletions theorems/T000553.md
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@@ -1,14 +1,9 @@
---
uid: T000553
if:
and:
- P000001: true
- P000090: true
- P000027: true
P000196: true
then:
P000057: true
P000042: true
---

In an {P90} space, the smallest basis is the set of smallest neighborhoods of points.
When it is also {P1}, these are all distinct, so they are in bijection with the set of points.
Thus, such a space has a countable basis iff it is countable.
Every subset of a {P196} space is {P40}, and {T38}.
2 changes: 1 addition & 1 deletion theorems/T000554.md
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Expand Up @@ -12,4 +12,4 @@ refs:
- doi: 10.1017/9781316543870
name: Spectral spaces (Dickmann, Schwartz, Tressl)
---
Shown in Proposition 1.6.7 of {{doi:10.1017/9781316543870}}.
Shown in Proposition 1.6.7 of {{doi:10.1017/9781316543870}}. In particular, it follows that the specialization order is order-isomorphic to a non-limit ordinal.
11 changes: 11 additions & 0 deletions theorems/T000555.md
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@@ -0,0 +1,11 @@
---
uid: T000555
if:
and:
- P000196: true
- P000176: true
then:
P000044: false
---

Since any subset is connected, any partition into non-singletons suffices.
12 changes: 12 additions & 0 deletions theorems/T000556.md
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@@ -0,0 +1,12 @@
---
uid: T000556
if:
and:
- P000196: true
- P000016: true
then:
P000146: true
---
If a {P196} space is {P16}, then it must have a second largest open set
(otherwise, $\mathcal T_X\setminus\{X\}$ would be totally ordered with no upper bound and therefore an open cover with no finite subcover).
Thus, any open cover must contain $X$, so it admits a refinement containing $X$ as the only nonempty set.
14 changes: 14 additions & 0 deletions theorems/T000557.md
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---
uid: T000557
if:
and:
- P000001: true
- P000090: true
- P000027: true
then:
P000057: true
---

In an {P90} space, the smallest basis is the set of smallest neighborhoods of points.
When it is also {P1}, these are all distinct, so they are in bijection with the set of points.
Thus, such a space has a countable basis iff it is countable.

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