anchor.diff:           ((eq player 'x)
               (setf move (make-move x report))
            )
  -         ((eq player 'y)
  +         ((eq player 'o)
               (setf move (make-move o report))
            )
         )
  
positive.code:       ((null (cdr l)) ())
        (t (cons (cadr l) (even (cddr l))))
     )
  )
  
  ; TODO
  
negative.code: )
  
  ; a random machine player and a human play one game
  (defmethod demo-random-human (&aux p x o)
     (setf x (make-instance 'random-machine-player))
     (setf o (make-instance 'human-player))
     (setf p (generic-play x o t))
  