Added some example facts.

This commit is contained in:
Bokuan Li
2026-06-03 16:56:40 -04:00
parent f72f815c72
commit 668679063b
7 changed files with 91 additions and 5 deletions

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@@ -70,6 +70,15 @@
Let $x \in E^c$. For each $y \in E$, there exists $U_y \in \cn(y)$ and $V_y \in \cn(x)$ such that $U_y \cap V_y = \emptyset$. By compactness, there exists $E_0 \subset E$ finite such that $\bigcup_{y \in E_0}U_y \supset E$. In which case, $E \cap \bigcap_{y \in E_0}V_y = \emptyset$ and $\bigcap_{y \in E_0}V_y \in \cn(x)$. Thus $E^c$ is open.
\end{proof}
\begin{proposition}
\label{proposition:compact-hausdorff-homeomorphism}
Let $X$ be a compact topological space, $Y$ be a Hausdorff space, and $f \in C(X; Y)$ be a bijection, then $f$ is a homeomorphism.
\end{proposition}
\begin{proof}
For each $K \subset X$ closed, $K$ and $f(K)$ are compact by \autoref{proposition:compact-extensions}. By \autoref{proposition:compact-closed}, $f(K)$ is closed. Thus $f^{-1}$ maps closed sets to closed sets, and hence open sets to open sets.
\end{proof}
\begin{proposition}
\label{proposition:compact-hausdorff-normal}
Let $X$ be a Hausdorff space, $A, B \subset X$ be compact with $A \cap B = \emptyset$, then there exists $U \in \cn(A)$ and $V \in \cn(B)$ such that $U \cap V = \emptyset$.

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@@ -25,7 +25,7 @@
\]
\end{enumerate}
Moreover, if $(\beta X, e)$ is \textit{any} pair that satisfies (1) and (U1), then
Moreover, if $(\beta X, e)$ is \textit{any} pair that satisfies (U1), then
\begin{enumerate}
\item[(U2)] For any pair $(Y, \varphi)$ satisfying (1), there exists a unique $\beta \varphi \in C(\beta X; Y)$ such that the following diagram commutes:
\[