(defun sqrt. (x)
 (newton (lambda (y) (- x (square x)))
          1))

(defun newton (f guess)
 (defun df (deriv f))
 (fixed-point
  (lambda (x) (- x (/ f x) (d f x))))
   guess))

(defun deriv
 (lambda (f)
  (lambda (x)
   (/ (- (f (+ x dx))
         (f x))
         dx))))

(defun dx  .00001)