diff --git a/introduction.tex b/introduction.tex
index 4602610..565fe43 100644
--- a/introduction.tex
+++ b/introduction.tex
@@ -40,6 +40,15 @@ this.<List<String>>emptyList().add(new List<String>())
     .get(0);
 \end{verbatim}
 
+$
+\begin{array}{c}
+TODO
+\\
+\hline
+\texttt{emptyList().get().get()} : \tv{a}
+\end{array} \quad \rulename{T-Call}
+$
+
 %motivate constraints: 
 To solve this example we will create constraints
 $