(define fact
  (lambda (n)
    (if (zero? n)
	1
	(* n (fact (- n 1))))))
(define nth-element
  (lambda (ls n)
    (if (null? ls)
	#f
	(if (zero? n)
	    (car ls)
	    (nth-element (cdr ls) (- n 1))))))

(nth-element '(a b c d e) 4)