Added a handful of examples.

src/op/banach/igroup.tex

@@ -26,10 +26,15 @@
     \sigma_A(x) \subset \complex \setminus e^{i\theta}[0, \infty)
     \]
 
-    then $x \in G_0(A)$. 
+    \begin{enumerate}
+        \item There exists $y \in A$ such that $x = \exp(y)$. 
+        \item $x \in G_0(A)$. 
+    \end{enumerate}
 \end{proposition}
 \begin{proof}
-    Since there exists a branch of the logarithm $\ell: \complex \setminus e^{i\theta}[0, \infty) \to \complex$, there exists $y \in A$ such that $x = \exp(y)$. In which case, $x \in G_0(A)$ by \autoref{proposition:functional-calculus-exp}. 
+    (1): Since there exists a branch of the logarithm $\ell: \complex \setminus e^{i\theta}[0, \infty) \to \complex$, there exists $y \in A$ such that $x = \exp(y)$. 
+    
+    (2): \autoref{proposition:functional-calculus-exp}. 
 \end{proof}