diff --git a/properties/P000245.md b/properties/P000245.md new file mode 100644 index 000000000..6004eb6c9 --- /dev/null +++ b/properties/P000245.md @@ -0,0 +1,16 @@ +--- +uid: P000245 +name: Has finitely many open sets +--- + +$X$ has finitely many open sets. + +Equivalently, the Kolmogorov quotient of $X$ is finite. + +---- +#### Meta-properties + +- This property is hereditary. +- This property is preserved in any coarser topology. +- $X$ is {P245} iff its Kolmogorov quotient $\text{Kol}(X)$ is {P78}. +- This property is preserved by finite products. diff --git a/theorems/T000189.md b/theorems/T000189.md index 45ab89a2c..2490a9563 100644 --- a/theorems/T000189.md +++ b/theorems/T000189.md @@ -3,13 +3,7 @@ uid: T000189 if: P000078: true then: - P000027: true -refs: -- zb: "0386.54001" - name: Counterexamples in Topology + P000245: true --- -Space is finite implies the topology is finite, hence countable. Thus the topology itself is a countable basis. - -Follows directly -from the definition on page 7 of {{zb:0386.54001}}. +Immediate from the definition. diff --git a/theorems/T000198.md b/theorems/T000198.md index 765a4a86e..e71e83b17 100644 --- a/theorems/T000198.md +++ b/theorems/T000198.md @@ -1,9 +1,9 @@ --- uid: T000198 if: - P000078: true + P000245: true then: P000208: true --- -Finite spaces are compact, and finiteness is a hereditary property. +Immediate from the definitions. diff --git a/theorems/T000251.md b/theorems/T000251.md index eeafd7371..f7ea2a8b6 100644 --- a/theorems/T000251.md +++ b/theorems/T000251.md @@ -3,10 +3,7 @@ uid: T000251 if: P000129: true then: - P000016: true -refs: - - mathse: 3844039 - name: What topological properties are trivially/vacuously satisfied by any indiscrete space? + P000245: true --- -All open covers are finite to begin with. +By definition. diff --git a/theorems/T000450.md b/theorems/T000450.md index 80d61ee8b..cdddf1368 100644 --- a/theorems/T000450.md +++ b/theorems/T000450.md @@ -1,12 +1,9 @@ --- uid: T000450 if: - P000129: true + P000245: true then: P000027: true -refs: - - mathse: 3844039 - name: What topological properties are trivially/vacuously satisfied by any indiscrete space? --- -A space with only finitely many open sets must by definition have a countable basis. +The topology is finite, hence countable. Thus the topology itself is a countable basis. diff --git a/theorems/T000658.md b/theorems/T000658.md index d601a4c6f..c5a86651b 100644 --- a/theorems/T000658.md +++ b/theorems/T000658.md @@ -5,7 +5,7 @@ if: - P000016: true - P000185: true then: - P000208: true + P000245: true --- -The ascending chain condition on open sets holds since there are only finitely many open sets. +The partition generating the topology must be finite due to $X$ being {P16}, so there are only finitely many open sets. diff --git a/theorems/T000823.md b/theorems/T000823.md index bc82ceba9..a719c447d 100644 --- a/theorems/T000823.md +++ b/theorems/T000823.md @@ -2,11 +2,10 @@ uid: T000823 if: and: - - P000016: true - - P000185: true + - P000245: true + - P000001: true then: - P000226: true + P000078: true --- -The partition generating the topology must be finite due to $X$ being {P16}. -Hence, there can only be finitely many open sets, which trivially implies {P226}. \ No newline at end of file +$\text{Kol}(X)$ is finite, and is equal to $X$ since $X$ is {P1}. So $X$ is finite. diff --git a/theorems/T000825.md b/theorems/T000825.md index ae671e426..6490824f9 100644 --- a/theorems/T000825.md +++ b/theorems/T000825.md @@ -1,7 +1,7 @@ --- uid: T000825 if: - P000078: true + P000245: true then: P000226: true ---