anchor.diff:  ;;  INPUTS
   ;;  SIDE-EFFECT: Destructively modify the game state by 
   ;;          capturing GROUP
  -(defun capture-group! (group game player)
  +(defun capture-group! (group game)
     ;;(format t "Capture group: ~A ~%" group)
  -  (let ((opponent (- 1 player)))
  +  (let* ((player (gg-whose-turn? game))
  +         (opponent (- 1 player))
  +         )
       ;; Remove the groups from the opponent's groups
       (setf (svref (gg-groups game) opponent) 
             (delete group (svref (gg-groups game) opponent)))
  
positive.code: ;; ----------------------------------------
  ;;  Undo the most recently played move
  (defun undo-move! (game)
    (format t "UNDO-MOVE ~A~%" game)
    (let* ((captured 0)
          (move (pop (gg-move-history game)))
          (pos (svref move 0))
          (player (gg-whose-turn? game)))
  
      ;; Unless the previous move was a pass
      (unless (= *board-size* pos)
        
        ;; Remove the piece from the board and from player's groups
        (pull-piece! game pos)
  
  
negative.code:             ;; Increment the capture flag
              (setq captured (+ 1 captured))
              ;; Capture the group
              (capture-group! group game))
            (when (= 1 (length (group-pieces group)))
              (setf (gg-ko? game) t)))
  
  