anchor.diff:  
   (defmethod glop:on-button (window pressed button)
     (declare (ignore window))
  -  (if pressed
  -      (format t "Button pressed: ~S~%" button)
  -      (format t "Button released: ~S~%" button)))
  +  (format t "Button ~:[released~;pressed~]: ~S~%" pressed button))
   
   (defmethod glop:on-mouse-motion (window x y dx dy)
     (declare (ignore window x y dx dy))
  
positive.code:            (gl:vertex 0.75 0.75 0)
             (gl:vertex 0.25 0.75 0))
           (gl:flush)
           (glop:swap-buffers win))))
negative.code: (in-package #:glop-test)
  
  (defmethod glop:on-key (window pressed keycode keysym string)
    (format t "Key ~:[released~;pressed~]: ~D (~S ~S)~%" pressed keycode keysym string)
    (when (eq keysym :escape)
      (glop:push-close-event window))
    (when (and pressed (eq keysym :f))
  