(defn sqrt-iter [guess x]
     (if(good-enough? guess x)
       guess
       (sqrt-iter (improve guess x)
                  x)))

(defn good-enough? [guess x]
     (< (abs (- (square guess) x)) 0.001))

(defn sqrt [x]
     (sqrt-iter 1.0 x))

//Usage:
(sqrt 9)