(defun n1   (&optional (x 1000))
  (if (< x 0) 
      0
      (+ x (n1 (- x 1)))))

(defun n2 ()
  (labels 
      ((n0 (x)
	 (if (< x 0)
	     0
	     (+ x (n0 (- x 1))))))
    (n0 1000)))

(defun n3 ()
  (do* ((x   1000 (1- x))
	(sum x    (+ sum x)))
       ((< x 0) sum)))
       
(defun ns ()
  (let ((r 100000)) 
    (print   t) (time (dotimes (i r) t)) 
    (print 'n1) (time (dotimes (i r) (n1))) 
    (print 'n2) (time (dotimes (i r) (n2))) 
    (print 'n3) (time (dotimes (i r) (n3)))))