Added the fundamental theorem of calculus.

src/topology/main/lch.tex

@@ -47,7 +47,7 @@
 
     As $\ol{W}$ is compact, it is normal by \autoref{proposition:compact-hausdorff-normal}. Since $X$ is Hausdorff, $K \subset \ol{W}$ is closed by \autoref{proposition:compact-closed}.
 
-    By \hyperref[Urysohn's lemma]{lemma:lch-urysohn}, there exists $f \in C(\ol{V}; [0, 1])$ such that $f|_K = 1$ and $f|_{\ol{W} \setminus V} = 0$. Let
+    By \hyperref[Urysohn's lemma]{lemma:urysohn}, there exists $f \in C(\ol{V}; [0, 1])$ such that $f|_K = 1$ and $f|_{\ol{W} \setminus V} = 0$. Let
     \[
     F: X \to [0, 1] \quad x \mapsto \begin{cases}
     f(x) &x \in W \\