anchor.diff:                             :image (make-instance 'image :name :enemy)
                              :health 4 :timer 20
                              :firepower (max 1 (ceiling w 3))
  -                           :difficulty (floor w 3))))))
  +                           :difficulty (floor w 5))))))
   
   (defmethod game-init ((game thopter-game))
     (let* ((size #c(800 600))
  
positive.code:       (let ((nearest-thopter (nearest-object enemy 'thopter))
              (nearest-health (nearest-object enemy 'health-pack))
              (nearest-bullet (nearest-object enemy 'bullet))
              (nearest-upgrade (nearest-object enemy 'upgrade-bullet))
              (r (- xy (/ (size (game-root *game*)) 2))))
          (setf v (* (unit v) (min (abs v) (+ 8d0 (* 2d0 difficulty))))
                accel
                (cond ((and nearest-thopter
                            (< (dist xy (offset nearest-thopter)) 180))
                       (toward nearest-thopter))
                      ((and nearest-health
                            (< (dist xy (offset nearest-health)) 180))
                       (toward nearest-health))
                      ((and nearest-bullet
                            (< (dist xy (offset nearest-bullet)) 120))
                       (* (away nearest-bullet)
                          (if (> health 1) 0.5d0 0.75d0)))
                      ((and nearest-upgrade
                            (< (dist xy (offset nearest-upgrade)) 180))
                       (toward nearest-upgrade))
                      (t (circular r))))))))
  
  (defmethod alarm ((enemy enemy) event)
  
negative.code:       (make-instance 'missile
                       :parent parent 
                       :offset (+ offset (/ (x size) 2) #c(0 -4)) :depth -1
                       :veloc (+ veloc #c(0 -4))
                       :image (make-instance 'image :name :missile)
                       :timer 120))))
  
  