anchor.diff:               :parent thopter
                :offset #c(-33 -22)
                :depth -1
  -             :image (make-anim "~a~a-~a" :thopter (mod i 4) :blades))
  +             :image blade-anim)
               (subscribe (game-keys screen) thopter)
               (incf (players-left (players-left screen)))))
       (let* ((tile-names '(:forest-0 :forest-1 :forest-2 :forest-3
  
positive.code:     (setf (ammo weapon) (* (ammo weapon) (ammo-deplete-rate weapon)))))
  
  (defmethod shoot ((weapon weapon) event)
    (with-slots ((shooter parent) projectile-class projectile-image
                 projectile-n-directions projectile-veloc projectile-timer
                 fire-sound ammo ammo-deplete-rate angle-increment
  
negative.code:    (firepower :initform nil)
     (ammo :initform 1)
     (ammo-refill-rate :initform 200)
     (ammo-deplete-rate :initform 200)
     (weapon-type :initform :straight)))
  
  (defclass missile-weapon (weapon)
    ((projectile-class :initform 'missile)
  