Fixed regex incident.

src/topology/main/regular.tex

@@ -7,7 +7,7 @@
     \begin{enumerate}
         \item For each $x \in X$ and $A \subset X$ closed with $x \not\in A$, there exists $U \in \cn(x)$ and $V \in \cn(A)$ such that $U \cap V = \emptyset$.
         \item For each $x \in X$, the closed neighbourhoods of $x$ forms a fundamental system of neighbourhoods at $x$.
-    \end\{enumerate\}
+    \end{enumerate}
 
     If $X$ is a T1 space such that the above holds, then $X$ is \textbf{regular}.
 \end{definition}