diff --git a/properties/P000233.md b/properties/P000233.md index ad53cc590..c3f895933 100644 --- a/properties/P000233.md +++ b/properties/P000233.md @@ -20,9 +20,11 @@ This is equivalent to each of the following: The equivalence between the various conditions can be shown by arguments similar to those used in the definition of {P42}, in particular {{mathse:3002235}}. -This property is used in the literature, but usually without a separate name. One exception is {{zb:0451.54017}}, where it is called "PCGS" (path connected generated space). +This property is used in the literature, but usually without a separate name. +One exception is {{zb:0451.54017}} (accessible [here](https://topology.nipissingu.ca/tp/reprints/v04/tp04204.pdf)), +where it is called "PCGS" (path connectedly generated space). -Compare with {P42}. +Compare with {P42} and {P234}. ---- #### Meta-properties diff --git a/properties/P000234.md b/properties/P000234.md new file mode 100644 index 000000000..db66d52a4 --- /dev/null +++ b/properties/P000234.md @@ -0,0 +1,35 @@ +--- +uid: P000234 +name: Has open connected components +refs: + - mathse: 3002235 + name: Answer to "Definition of locally pathwise connected" + - zb: "0451.54017" + name: Topologies determined by paths (S. Franklin, B. Smith-Thomas) +--- + +Every connected component of $X$ is open. + +This is equivalent to each of the following: + +* Each point $x\in X$ has a connected neighborhood. + +* Each point $x\in X$ has an open connected neighborhood. + +* $X$ is a topological disjoint union of {P36} spaces. + +The equivalence between the various conditions can be shown by arguments similar to those used in the definition of {P42}, in particular {{mathse:3002235}}. + +This property is normally used without a separate name. But see {{zb:0451.54017}} +(accessible [here](https://topology.nipissingu.ca/tp/reprints/v04/tp04204.pdf)), +where it is called "CGS" (connectedly generated space). + +Compare with {P41} and {P233}. + +---- +#### Meta-properties + +- $X$ satisfies this property iff its Kolmogorov quotient $\text{Kol}(X)$ does. +- This property is hereditary with respect to clopen sets. +- This property is preserved by finite products. +- This property is preserved by arbitrary disjoint unions. diff --git a/theorems/T000108.md b/theorems/T000108.md index 2249e517b..0be0af4c2 100644 --- a/theorems/T000108.md +++ b/theorems/T000108.md @@ -2,15 +2,11 @@ uid: T000108 if: and: + - P000234: true - P000047: true - - P000041: true then: P000052: true -refs: -- zb: "0386.54001" - name: Counterexamples in Topology --- -If every point has a connected neighborhood and the only connected sets are single points, then every point has a neighborhood consisting of the point itself. - -Proven on page 32 of {{zb:0386.54001}}. +By {P47} the connected components of $X$ are singletons, +so by {P234} every singleton is open. diff --git a/theorems/T000862.md b/theorems/T000862.md new file mode 100644 index 000000000..f7aef0b55 --- /dev/null +++ b/theorems/T000862.md @@ -0,0 +1,9 @@ +--- +uid: T000862 +if: + P000233: true +then: + P000234: true +--- + +Immediate from the (equivalent) definitions using {T40}. diff --git a/theorems/T000863.md b/theorems/T000863.md new file mode 100644 index 000000000..fd9df3cc4 --- /dev/null +++ b/theorems/T000863.md @@ -0,0 +1,9 @@ +--- +uid: T000863 +if: + P000041: true +then: + P000234: true +--- + +Immediate from the definitions. diff --git a/theorems/T000864.md b/theorems/T000864.md new file mode 100644 index 000000000..a6703884a --- /dev/null +++ b/theorems/T000864.md @@ -0,0 +1,9 @@ +--- +uid: T000864 +if: + P000036: true +then: + P000234: true +--- + +Immediate from the definitions.