Title: Mine was when I learned a subset of recursion called mutual recursion. It was for a pair of function to determine if a number was odd or even.<p>(define (odd? x)<p><pre><code>  (cond


    [(zero? x) #f]


    [else (even? (sub1 x))]))

</code></pre>
(define (even? x)<p><pre><code>  (cond


    [(zero? x) #t]


    [else (odd? (sub1 x))]))</code></pre>
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