2.62.tex

\documentclass[a4paper,12pt]{article}
\usepackage{listings}
\lstset{language=Lisp}

\begin{document}
\begin{lstlisting}
(define (union-set set1 set2)
  (define (iter res set1 set2)
    (cond ((null? set1)
           (foldl cons set2 res))
          ((null? set2)
           (foldl cons set1 res)) 
          (else
           (let ((x1 (car set1)) (x2 (car set2)))
            (cond ((< x1 x2)
                   (iter (cons x1 res)
                         (cdr set1)
                         set2))
                  ((= x1 x2)
                   (iter (cons x1 res)
                         (cdr set1)
                         (cdr set2)))
                  (else
                   (iter (cons x2 res)
                         set1
                         (cdr set2))))))))
  (iter '() set1 set2))
\end{lstlisting}
\end{document}