\begin{flushleft}
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\vspace*{-4mm}

\begin{alltt}
STk> (define dg (digraph '(1 2 3 4) '((1 2 3) (2 3 4)))){\em{
\#[undefined]} }
\end{alltt}
\begin{alltt}
STk> (define n (neighbors (vertex-ref dg 1))){\em{
\#[undefined]} }
\end{alltt}
\begin{alltt}
STk> (describe (vertex-ref dg 1)){\em{
\#[\(<\)vertex*\(>\) \#p4fa7d8] is an instance of class \(<\)vertex*\(>\)
Slots are: 
     val = 2
\#f} }
\end{alltt}
\begin{alltt}
STk> (describe n){\em{
\#[\(<\)set\(<\)vertex*\(>\)\(>\) \#p503118] is an instance of class \(<\)set\(<\)vertex*\(>\)\(>\)
Slots are: 
     val = \{1 3 4\}
\#f} }
\end{alltt}
\begin{alltt}
STk> (define in (in-neighbors (vertex-ref dg 1))){\em{
\#[undefined]} }
\end{alltt}
\begin{alltt}
STk> (describe in){\em{
\#[\(<\)set\(<\)vertex*\(>\)\(>\) \#p4f94e8] is an instance of class \(<\)set\(<\)vertex*\(>\)\(>\)
Slots are: 
     val = \{1\}
\#f} }
\end{alltt}
\begin{alltt}
STk> (define out (out-neighbors (vertex-ref dg 1))){\em{
\#[undefined]} }
\end{alltt}
\begin{alltt}
STk> (describe out){\em{
\#[\(<\)set\(<\)vertex*\(>\)\(>\) \#p4f8708] is an instance of class \(<\)set\(<\)vertex*\(>\)\(>\)
Slots are: 
     val = \{3 4\}
\#f} }
\end{alltt}

\vspace*{-5mm}

\hrulefill
\end{flushleft}