(define approximate-sqrt
  (lambda (x tolerance)
    (define find-approximation-from
      (lambda (starting-point)
        (if (good-enough? starting-point)
            starting-point
            (find-approximation-from (improve starting-point)))))
    (define good-enough?
      (lambda (approximation)
        (<= (- 1 tolerance)
            (/ (square approximation) x) 
            (+ 1 tolerance)))) 
    (define improve
      (lambda (approximation)
        (/ (+ (/ x approximation) approximation)
           2)))
    (find-approximation-from 1)))

(define square
  (lambda (x)
    (* x x)))