Start let insert example

introduction.tex

@@ -45,7 +45,30 @@ List<?> genList() {
       \end{subfigure}
       %\caption{Example code}
       %\label{fig:intro-example-code}
-    \end{figure}
+\end{figure}
+
+
+In \cite{WildcardsNeedWitnessProtection} existential types have to be \textit{unpacked} before they can be used.
+Our type inference algorithm has to add let statements surrounding method invocations.
+\begin{figure}[tp]
+      \begin{subfigure}[t]{0.49\linewidth}
+    \begin{lstlisting}[style=fgj]
+    List<? super Integer> ls = ...;
+    ls.add(new Integer());
+    \end{lstlisting}
+        \caption{Method invocation}
+        \label{fig:intro-example-typeless}
+      \end{subfigure}
+      ~
+      \begin{subfigure}[t]{0.49\linewidth}
+    \begin{lstlisting}[style=tfgj]
+    List<? super Integer> ls = ...;
+    ls.add(new Integer());
+    \end{lstlisting}
+        \caption{Capture Conversion by \texttt{let}-statement}
+        \label{fig:intro-example-typed}
+      \end{subfigure}
+\end{figure}
 
 % \subsection{Wildcards}
 % Java subtyping involving generics is invariant.