anchor.diff:     (target-location :initform nil :accessor target-location)
      (structure :initarg :structure :accessor enemy-structure)
      (death-tick :initform nil :accessor death-tick)
  -   (growth-tick :initform nil :accessor growth-tick)))
  +   (growth-tick :initform nil :accessor growth-tick)
  +   (growth-rate :initarg :growth-rate :accessor growth-rate)
  +   (max-size :initarg :max-size :accessor max-size)))
   
   (defmethod update ((enemy enemy))
     (let ((location (cell-location (pos enemy))))
  
positive.code: 
  
  ;;;; Level timer
  
  (defconstant* enemy-growth-ticks 1000)
  
  (defclass level-timer ()
    ())
  
  (defmethod update ((timer level-timer))
    (when (and (plusp *tick*)
               (zerop (mod *tick* enemy-growth-ticks)))
      (do-objects (enemy :type 'enemy)
        (enemy-grow enemy))))
  
  
  ;;;; Game
  
  (defclass consix-window (game-window)
  
negative.code: 
  (define-level (consix :test-order '(player enemy t))
    (grid :named grid)
    (player :lives 3 :loc (location (1- grid-rows) (floor grid-cols 2)) :grid grid)
    (enemy :pos (vec -10 0) :structure (list 0.0) :grid grid :growth-rate 1000 :max-size 8)
    (enemy :pos (vec +10 0) :structure (list 0.0) :grid grid :growth-rate 1000 :max-size 8))
  
  (defun game ()
    (glut:display-window
  