Small adjustments.
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Bokuan Li
2026-07-01 00:04:11 -04:00
parent 89ec2234be
commit 1caa2785ef

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@@ -188,14 +188,14 @@
\item[(b)] For every $x \in X_E$, $N_x \cap E \ne \emptyset$.
\end{enumerate}
Let $X_{\ce} = \bigcup_{E \in \ce}X_\ce$, and for each $E \in \ce$, let
Let $X_{\ce} = \bigcup_{E \in \ce}X_E$, and for each $E \in \ce$, let
\[
G_E = \bigcup_{\substack{x \in X_\ce \\ \ol{N_x} \subset E}}N_x
\]
then $\bracs{G_E}_{E \in \ce}$ is an open cover of $X$. Since $G_E \subset E$ for all $E \in \ce$, $\bracs{G_E}_{E \in \ce}$ is locally finite.
It remains to show that $\ol{G_E} \subset E$. Let $x \in X_F$ such that $N_x \subset E$, then $N_x \cap F \ne \emptyset$. Since $N_x \subset E$, $E \cap F \ne \emptyset$. Thus
It remains to show that $\ol{G_E} \subset E$. Let $F \in \ce$ and $x \in X_F$ such that $N_x \subset E$, then $N_x \cap F \ne \emptyset$ and $E \cap F \ne \emptyset$. Thus
\[
\bracsn{x \in X_\ce|\ol{N_x} \subset E} \subset \bigcup_{\substack{F \in \ce \\ E \cap F \ne \emptyset}}X_F \subset \bigcup_{\substack{F \in \ce \\ \ol E \cap F \ne \emptyset}}X_F
\]