anchor.diff:  (defvar *new-game* "#new-game")
   
   (defvar *cell-count* 9)
  +(defvar *levels*     '(:novice :intermediate :experienced))
  +(defvar *level*      (third *levels*))
   (defvar *player-1*   :human)
   (defvar *player-2*   :computer)
   
  
positive.code:   (let ((state (state x-o)))
      (dolist (row *win-rows*)
        (let ((i (position (- row (logand state row)) ; bit logic
                           #.(quote (loop :for i :below 9 :collect (s i))))))
          (when (and i (x:empty-string (cell-text i)))
            (return-from check-win-move i))))))
  
  
negative.code:   (:export
     #:*board*
     #:*cells*
     #:*level*
     #:*levels*
     #:*new-game*
     #:*player-1*
     #:*player-2*
  