diff options
Diffstat (limited to 'library/topology/disconnection.tex')
| -rw-r--r-- | library/topology/disconnection.tex | 18 |
1 files changed, 13 insertions, 5 deletions
diff --git a/library/topology/disconnection.tex b/library/topology/disconnection.tex index e3730f3..90c635d 100644 --- a/library/topology/disconnection.tex +++ b/library/topology/disconnection.tex @@ -23,10 +23,14 @@ Then there exists a disconnection of $X$. \end{proposition} \begin{proof} - Take $U, V\in\opens[X]$ such that $\carrier[X]$ is partitioned by $U$ and $V$ + Take $U,V$ such that $U,V\in\opens[X]$ and + $\carrier[X]$ is partitioned by $U$ and $V$ by \cref{disconnected}. - Then $(U, V)$ is a bipartition of $\carrier[X]$. - Thus $(U, V)$ is a disconnection of $X$ by \cref{disconnections,times_proj_elim,times_tuple_intro}. + $(U,V)$ is a bipartition of $\carrier[X]$ by \cref{bipartition_intro}. + $\fst{(U,V)}=U$ by \cref{fst_eq}. + $\snd{(U,V)}=V$ by \cref{snd_eq}. + $(U,V)\in\disconnections{X}$ by \cref{disconnections}. + Follows by assumption. \end{proof} \begin{proposition}\label{disconnected_from_disconnection} @@ -35,8 +39,12 @@ Then $X$ is disconnected. \end{proposition} \begin{proof} - $\fst{D}, \snd{D}\in\opens[X]$. - $\carrier[X]$ is partitioned by $\fst{D}$ and $\snd{D}$. + $D\in\disconnections{X}$ by assumption. + $D\in\bipartitions{\carrier[X]}$ by \cref{disconnections}. + $\fst{D},\snd{D}\in\opens[X]$ by \cref{disconnections}. + $\carrier[X]$ is partitioned by $\fst{D}$ and $\snd{D}$ + by \cref{bipartitions_of_a_set}. + Follows by \cref{disconnected}. \end{proof} \begin{abbreviation}\label{connected} |
