anchor.diff:  
   (defmethod medium-draw-bezier-design* ((medium render-medium-mixin)
                                                        (design bezier-union))
  -  (let ((tr (transformation design)))
  -    (dolist (area (areas design))
  -      (%medium-draw-bezier-design medium (transform-region tr area) t))))
  +  (dolist (area (areas design))
  +    (%medium-draw-bezier-design medium area t)))
   
   (defmethod medium-draw-bezier-design* ((medium render-medium-mixin)
                                                        (design bezier-difference))
  -  (let ((tr (transformation design)))
  -    (dolist (area (positive-areas design))
  -      (%medium-draw-bezier-design medium (transform-region tr area) t))
  -    (dolist (area (negative-areas design))
  -      (with-drawing-options (medium :ink +background-ink+)
  -        (%medium-draw-bezier-design medium (transform-region tr area) t)))))
  +  (dolist (area (positive-areas design))
  +    (%medium-draw-bezier-design medium area t))
  +  (dolist (area (negative-areas design))
  +    (with-drawing-options (medium :ink +background-ink+)
  +      (%medium-draw-bezier-design medium area t))))
   
   ;;; Postscript backend
   
  
positive.code:     :negative-areas (list r2)))
  
  (defmethod region-difference ((r1 bezier-area) (r2 bezier-union))
    (let ((tr (transformation r2)))
      (make-instance 'bezier-difference
        :positive-areas (list r1)
        :negative-areas (mapcar (lambda (r) (transform-region tr r)) (areas r2)))))
  
  (defmethod region-difference ((r1 bezier-union) (r2 bezier-area))
    (let ((tr (transformation r1)))
      (make-instance 'bezier-difference
        :positive-areas (mapcar (lambda (r) (transform-region tr r)) (areas r1))
        :negative-areas (list r2))))
  
  (defmethod region-difference ((r1 bezier-union) (r2 bezier-union))
    (let ((tr1 (transformation r1))
          (tr2 (transformation r2)))
      (make-instance 'bezier-difference
        :positive-areas (mapcar (lambda (r) (transform-region tr1 r)) (areas r1))
        :negative-areas (mapcar (lambda (r) (transform-region tr2 r)) (areas r2)))))
  
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  ;;;
  
negative.code: 
  (defgeneric ensure-pixmap (medium design))
  
  (defmethod ensure-pixmap (medium design)
    (let* ((pixmap (gethash (list (medium-sheet medium) (resolve-ink medium) design)
  			 *pixmaps*)))
      (when (null pixmap)
        (let* ((picture (render-to-array design))
  