anchor.diff:  ;;;   Created: 1998-12-02 19:26
   ;;;    Author: Gilbert Baumann <unk6@rz.uni-karlsruhe.de>
   ;;;   License: LGPL (See file COPYING for details).
  -;;;       $Id: regions.lisp,v 1.19 2002-06-04 07:50:20 adejneka Exp $
  +;;;       $Id: regions.lisp,v 1.20 2002-06-12 03:43:41 adejneka Exp $
   ;;; --------------------------------------------------------------------------------------
   ;;;  (c) copyright 1998,1999,2001 by Gilbert Baumann
   ;;;  (c) copyright 2001 by Arnaud Rouanet (rouanet@emi.u-bordeaux.fr)
  
positive.code: 
  (defmethod region-intersection ((a standard-region-intersection) (b region))
    (region-intersection b a))
  
  
  (defmethod region-intersection ((x region) (y standard-region-difference))
  
negative.code:   (make-instance 'standard-region-union 
      :regions (append (standard-region-set-regions a) (standard-region-set-regions b))))
  
  (defmethod region-union ((a region) (b region))
    (make-instance 'standard-region-union :regions (list a b)))
  
  (defmethod region-union ((a standard-rectangle-set) (b path)) a)
  (defmethod region-union ((b path) (a standard-rectangle-set)) a)
  (defmethod region-union ((a standard-rectangle-set) (b point)) a)
  