Various typo fixes.

src/dg/derivative/taylor.tex

@@ -141,7 +141,7 @@
     [r(h)]_F \le \frac{1}{(n+1)!} \cdot \sup_{t \in [0, 1]}[D^{n+1}_\sigma f(x_0 + th)(h^{n+1})]
     \]
 \end{theorem}
-\begin{proof}{Proof, {{\cite[Section XIII.6]{Lang}}}. }
+\begin{proof}[Proof, {{\cite[Section XIII.6]{Lang}}}. ]
     Firstly, if $n = 0$, then by the \hyperref[Fundamental Theorem of Calculus]{theorem:ftc-riemann}, 
     \[
     f(x_0 + h) - f(x_0) = \int_0^1 D_\sigma f(x_0 + th)(h) dt