Cube root in lisp (SICP ex 1.8)

croot.lisp

(define (croot x)
        (croot-iter 1.00 x))
 
 (define (croot-iter guess x)
         (if (good-enough? guess x)
             guess
             (croot-iter (improve guess x)
                        x)))
 
 (define (improve guess x)
         (/ (+ (/ x (square guess))
               (* 2 guess))
            3))

 (define (cube x)
         (* x x x))
 
 (define (good-enough? guess x)
         (< (abs (- (cube guess) x))
            0.001))