diff --git a/properties/P000208.md b/properties/P000208.md index cf8152070..960676a06 100644 --- a/properties/P000208.md +++ b/properties/P000208.md @@ -31,6 +31,8 @@ Compare with {P226}. #### Meta-properties - This property is hereditary. +- $X$ satisfies this property iff its Kolmogorov quotient $\text{Kol}(X)$ does. - This property is preserved by finite products (see Theorem 3 in {{mathse:5118758}}). - This property is preserved by finite disjoint unions. - This property is preserved in any coarser topology. + diff --git a/theorems/T000929.md b/theorems/T000929.md new file mode 100644 index 000000000..c66dab7b4 --- /dev/null +++ b/theorems/T000929.md @@ -0,0 +1,23 @@ +--- +uid: T000929 +if: + and: + - P000073: true + - P000090: true +then: + P000051: true +--- + +$X$ is {P1} since {T174}. +Let $\le$ denote the corresponding specialization order ($x\le y \iff x\in\overline{\{y\}})$). +Given a point $a\in X$, its smallest neighborhood is ${\uparrow}a:=\{x\in X:x\ge a\}$. + +Assume by contradiction that $X$ is not {P51}. +There is a nonempty set $A\subseteq X$ such that the subspace $A$ has no isolated point; +hence for each $a\in A$ we have ${\uparrow} a\cap A\supsetneq\{a\}$, that is, there is some $b\in A$ with $a