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Decrementing a number: `pred'
This abstraction determines the predecessor of a natural number, which corresponds
to decrementing it.
![\begin{lstlisting}[language=Scm]{}
(define pred (lambda (n)
(cdr ((n (lambda (x)
(cons (add (car x) one)
(car x))))
zeropair))))
\end{lstlisting}](img104.gif)
![\begin{lstlisting}[language=Scm]{}
(ndisp! (pred one))
--> 0
(ndisp! (pred three))
--> 2
\end{lstlisting}](img105.gif)
Georg P. Loczewski
2004-03-05