Cleaned up MCT in measure.

src/measure/lebesgue-integral/simple.tex

@@ -18,7 +18,7 @@
 
 \begin{proposition}
 \label{proposition:lebesgue-simple-properties}
-    Let $(X, \cm, \mu)$ be a measure space and $f, g \in \Sigma^*(X, \cm)$, then:
+    Let $(X, \cm, \mu)$ be a measure space and $f, g \in \Sigma^+(X, \cm)$, then:
     \begin{enumerate}
         \item For any $\alpha \ge 0$, $\int \alpha f d\mu = \alpha \int f d\mu$.
         \item $\int f + g d\mu = \int f d\mu + \int g d\mu$.