anchor.diff:  
   (defmethod reverse-path ((path bezier-area))
     (make-instance 'bezier-area
  -    :segments (reverse (mapcar #'reverse-segment (%segments path)))
  -    :transformation (transformation path)))
  -
  -;;; slanting transformation are used by Metafont
  -(defun make-slanting-transformation (slant)
  -  (make-transformation 1.0 slant 0.0 1.0 0.0 0.0))
  +    :segments (reverse (mapcar #'reverse-segment (%segments path)))))
  +
   
   ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
   ;;;
  
positive.code: 
  ;;; A union of bezier areas.  This is not itself a bezier area.
  (defclass bezier-union (area bezier-design)
    ((%trans :initarg :transformation
  	   :reader transformation
  	   :initform +identity-transformation+)
     (%areas :initarg :areas :initform '() :reader areas)))
  
  (defmethod transform-region (transformation (union bezier-union))
    (let* ((tr (transformation union))
           (new-tr (compose-transformations transformation tr))
           (result (if (translation-transformation-p transformation)
                       (make-instance 'bezier-union
  		       :areas (areas union)
  		       :transformation new-tr)
                       (make-instance 'bezier-union
  		       :areas (loop for area in (areas union)
  				    collect (transform-region new-tr area))))))
      (when (translation-transformation-p transformation)
        (setf (original-region result) (or (original-region union) union)))
      result))
  
  (defun bounding-rectangle-of-areas (areas)
    (multiple-value-bind (final-min-x final-min-y final-max-x final-max-y)
  
negative.code:     :negative-areas (list r2)))
  
  (defmethod region-difference ((r1 bezier-area) (r2 bezier-union))
    (make-instance 'bezier-difference
                   :positive-areas (list r1)
                   :negative-areas (areas r2)))
  
  (defmethod region-difference ((r1 bezier-union) (r2 bezier-area))
    (make-instance 'bezier-difference
                   :positive-areas (areas r1)
                   :negative-areas (list r2)))
  
  (defmethod region-difference ((r1 bezier-union) (r2 bezier-union))
    (make-instance 'bezier-difference
                   :positive-areas (areas r1)
                   :negative-areas (areas r2)))
  
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  ;;;
  