anchor.diff:    (bind-key-up   thopter :sdl-key-left  #'stop-west)
     (bind-key-down thopter :sdl-key-right #'move-east)
     (bind-key-up   thopter :sdl-key-right #'stop-east)
  -  (bind-key-down thopter :sdl-key-space #'shoot)
  +  (bind-key-down thopter :sdl-key-space #'start-shoot)
  +  (bind-key-up thopter :sdl-key-space #'stop-shoot)
     (bind-key-down thopter :sdl-key-lctrl #'missile)
     (bind-key-down thopter :sdl-key-lalt  #'missile)
     ;; TODO: add reset function
  
positive.code:     :initarg :firepower
      :initform 1)))
  
  (defclass thopter (sprite mobile collidable shooter)
    ((bullet-class :initform 'bullet)
     (bullet-image :initform (make-instance 'image :name :bullet))
     (bullet-veloc :initform #c(0 -8))
     (bullet-timer :initform 60)
     (health
      :accessor health
      :initarg :health
  
negative.code:                        :offset (complex (/ (x size) 2) (* (y size) 3/4))
                         :image (make-instance 'anim :name :thopter)
                         :health 4 :firepower 3 :missiles 2)))
           (subscribe (game-keys game) thopter)))
        ((:server :client)
          (let ((thopter1 (make-instance
  