anchor.diff:  (defun enemy-kill-player (enemy)
     (declare (ignore enemy))
     (do-objects (player :type 'player)
  -    (player-die player)))
  +    (when (null (death-tick player))
  +      (setf (death-tick player) 0))))
   
   (defun enemy-die (enemy)
     (setf (death-tick enemy) 0)
  
positive.code:          (setf (claiming-p player) nil)
           (setf (loc player) (initial-location player))
           (setf (pos player) (cell-center-position (initial-location player)))
           (setf (movement-actions player) '()))
          (t (outer-world))))
  
  (defun increment-score (increment player)
  
negative.code:    (movement-actions :initform '() :accessor movement-actions)
     (claiming :initform nil :accessor claiming-p)
     (lives :initarg :lives :accessor lives)
     (score :initform 0 :accessor score)
     (death-tick :initform nil :accessor death-tick)))
  
  (defmethod initialize-instance :after ((player player) &rest initargs)
    (declare (ignore initargs))
    (setf (pos player) (cell-center-position (initial-location player))))
  
  (defmethod update ((player player))
    (cond ((death-tick player)
           (when (= (incf (death-tick player)) player-death-ticks)
             (player-die player)))
          (t
           (when (null (movement-actions player))
             (maybe-queue-movement-actions player))
           (when-let (action (pop (movement-actions player)))
             (funcall action))
           (halo-update (halo player)))))
  
  (defmethod render ((player player))
    (gl:color 1.0 1.0 1.0)
    (display-text -90 93 "Score: ~9,'0D" (score player))
    (flet ((draw (x y &optional draw-halo (alpha-multiplier 1.0))
             (gl:with-pushed-matrix
               (gl:translate x y 0.0)
               (dotimes (i 5)
                 (gl:color 0.0 0.0 1.0 (* alpha-multiplier i 0.2))
                 (draw-circle (- 5 i) 30 t))
               (when draw-halo
                 (gl:color 0.0 0.0 1.0 (halo-value (halo player)))
                 (draw-circle 5)))))
      (with-vec (x y (pos player))
        (draw x y (not (claiming-p player))
              (- 1.0 (/ (or (death-tick player) 0.0)
                        player-death-ticks))))
      (dotimes (i (lives player))
        (draw -95.0 (- 85.0 (* i 10.0))))))
  
  