(element-of? 'foo '(1 3 5 foo 9)) ⇒ #t

     (element-of? 'bar '(1 3 5 foo 9)) ⇒ #f

     (define element-of?
       (lambda (item lst)
         (if (null? lst)
             #f
             (if (equal? (car lst) item)
                 #t
                 (element-of? item (cdr lst))))))