anchor.diff:  ;; ----------------------------------------
   ;;  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)))
  +         (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)
   
  
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: 
        ;; If necessary return captured groups
        (when (< 0 (svref move 1))
          (format t "Player caps: ~A, Oppo Caps ~A, Move: ~A~%" 
                  (svref (gg-captures game) player)
                  (svref (gg-captures game) opponent)
                  move)
  
          ;; Return each captured group
          (dotimes (i (svref move 1))
            (let ((group (pop (svref (gg-captures game) opponent)))
                          )              
              (format t "Group: ~A~%" group )
              ;; Add the group's pieces to the board
              (dolist (p (group-pieces group))
                (format t "Piece: ~A~%" p)
                (setf (svref (gg-board game) p) (+ 1 player)))
  
              (push group (svref (gg-groups game) player))
  
              ;; Evaluate each players score
              (eval-subtotals! game)))
        ))
      ;; Change turn
      (setf (gg-whose-turn? game) opponent)
      ))
  
  ;;  PULL-PIECE!  -- used by UNDO-MOVE!
  ;; ---------------------------------------------------------------
  