anchor.diff:    (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))))))
  +                         '#.(loop :for i :below 9 :collect (s i)))))
           (when (and i (x:empty-string (cell-text i)))
             (return-from check-win-move i))))))
   
  
positive.code:   "Sum of binary shifted numbers."
    (apply '+ (mapcar (lambda (x) (ash 1 x)) numbers)))
  
  (defvar *win-rows* (list (s 0 1 2) (s 3 4 5) (s 6 7 8) ; horizontal
                           (s 0 3 6) (s 1 4 7) (s 2 5 8) ; vertical
                           (s 0 4 8) (s 2 4 6)))         ; X
  
  (let (latest)
    (defun state (x-o)
  
negative.code:   (:export
     #:*board*
     #:*cells*
     #:*level*
     #:*levels*
     #:*new-game*
     #:*player-1*
     #:*player-2*
  