anchor.diff:                       :parent parent 
                        :offset (+ offset (/ (x size) 2) #c(0 -4)) :depth -1
                        :veloc veloc
  -                     :image (make-instance 'image :name :missile-n)
  -                     :timer 120))))
  +                     :image (make-instance 'image :name :missile-n)))))
   
   (defmethod update ((missile missile) event)
     (with-slots (parent offset size veloc accel image) missile
  
positive.code:   (when (and (parent bullet) (typep (event-hit event) 'enemy))
      (detach (parent bullet) bullet)))
  
  (defmethod collide ((missile missile) event)
    (with-slots (parent offset size depth veloc) missile
      (when (and parent (or (typep (event-hit event) 'enemy)
  
negative.code: 
  (defmethod collide ((bullet enemy-bullet) event)
    (when (and (parent bullet) (typep (event-hit event) 'thopter))
      (detach (parent bullet) bullet)))
  
  (defmethod alarm ((bullet enemy-bullet) event)
    (when (parent bullet)
      (detach (parent bullet) bullet)))
  
  (defmethod update ((enemy enemy) event)
  