(defun goodenough (guess x)(< (abs (- (* guess guess) x)) 0.001))
(defun improve (guess x) (average guess (/ x guess)))
(defun average (x y) (/ (+ x y) 2))
(defun sqlt_it (guess x)
 (if (goodenough guess x)
      guess
    (sqlt_it (improve guess x) x)))

(sqlt_it 1.0 5)
2.2360688956433634