(define times3
  (lambda (n)
    (* 3 n)))
(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))))))