Fix abs value to norm (V's are vectors)

chapter4-disc.tex

@@ -650,7 +650,7 @@ \subsection{Error bounds and stopping rules:}
 \begin{lemma}
  If $\|\Value_{n+1}-\Value_{n}\|_\infty < \epsilon \cdot \frac{1-\discount}{2\discount}$ then $\|\Value_{n+1} -
 \Value^{*}\|_\infty < \frac{\varepsilon}{2}$ and
-$|\Value^{\policy_{n+1}}-\Value^*|\leq \varepsilon$, where
+$\|\Value^{\policy_{n+1}}-\Value^*\|\leq \varepsilon$, where
 $\policy_{n+1}$ is the greedy policy w.r.t. $\Value_{n+1}$.
 \end{lemma}
 \begin{proof}