Локальные функции

(defun sqrt2 (x)
  (labels ((good-enough-p (guess)
             (<= (abs (- (square guess) x)) 0.001))
           (improve (guess)
             (average guess (/ x guess)))
           (sqrt-iter (guess)
             (if (good-enough-p guess)
                 guess
                 (sqrt-iter (improve guess)))))
    (sqrt-iter 1.0)))
Преимущества