(defun hilo (choice low high)
"Hi-Lo Game: a recursive bug-free binary 
                        search algorithm implementation."
(let*
    ((x (+ low (/ (- high low) 2))))
  (cond (
         (< x choice) 
         (hilo choice x high))
        ((> x choice) 
         (hilo choice low x))
        ((= x choice) 
         (message  (number-to-string x)))
)))