Start let insert example

introduction.tex

@@ -47,6 +47,29 @@ List<?> genList() {
       %\label{fig:intro-example-code}
 \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.
 % For example \texttt{List<String>} is not a subtype of \texttt{List<Object>}.