diff --git a/theorems/T000552.md b/theorems/T000552.md index 4c3be64db..ab728be17 100644 --- a/theorems/T000552.md +++ b/theorems/T000552.md @@ -2,12 +2,10 @@ uid: T000552 if: and: - - P000196: true - - P000016: true + - P000146: true + - P000036: true - P000086: true 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}. +Any clopen partition of a {P36} space $X$ must contain $X$, so to admit clopen refinements every open cover must contain $X$. Thus, the union of all open sets except for $X$ cannot equal $X$ (as that would be an open cover not containing $X$), so some points have $X$ as their only neighborhood. By homogeneity, this must then be true of all points, i.e. the space is {P129}.