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