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-rw-r--r--library/topology/disconnection.tex18
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}