(define times3
  (lambda (n)
    (* n 3)))
(define times6
  (lambda (m)
    (+ (times3 m) (times3 m))))
(define fact
  (lambda (n)
    (if (zero? n)
	1
	(* n (fact (- n 1))))))

(define nth-element
  (lambda (ls n)
    (if (null? ls)
	       "error"
	       (if (zero? n)
		   (car ls)
		   (nth-element (cdr ls) (- n 1)))))))