(element-of? 'foo '(1 3 5 foo 9)) ⇒ #t
(element-of? 'bar '(1 3 5 foo 9)) ⇒ #f
Another way to write it:
(define element-of?
(lambda (item lst)
(cond ((null? lst)
#f)
((equal? (car lst) item)
#t)
(else
(element-of? item (cdr lst))))))