updates

content/Math4201/Math4201_L32.md

@@ -105,7 +105,7 @@ Since $V$ is open in $Y$, then $K$ is closed in $Y$. Since $Y$ is compact, then
 
 Let $X$ be a topological space, then $X$ satisfies the first countability axiom if
 
-For any $x\in X$, there is a countable collection $\{B_n}_n$ of open neighborhoods of $x$ such that any open neighborhood $U$ of $x$ contains one of $B_n$.
+For any $x\in X$, there is a countable collection $\{B_n\}_n$ of open neighborhoods of $x$ such that any open neighborhood $U$ of $x$ contains one of $B_n$.
 
 <details>
 <summary>Example for metric space satisfies the first countability axiom</summary>