1 (defvar *tolerance* 0.00001)
2 (defun fixed-point (f first-guess)
3   (labels (
4 	   (close-enough? (v1 v2)
5 			  (< (abs (- v1 v2)) *tolerance*))
6 	   (try (guess)
7 		(let ((next (funcall f guess)))
8 		  (if (close-enough? guess next)
9 		      next
10 		    (try next)))))
11 	  (try first-guess)))
12 (defun average (a b)
13   (/ (+ a b) 2))
14 
15 (defun dampen-sqrt (x)
16   (fixed-point
17    (lambda (y)
18      (average y (/ x y)))
19    1.0))
20 
21 (defun dampen-root (x n)
22   (fixed-point
23    (lambda (y)
24      (average y (/ x (expt y (1- n)))))
25    1.0))