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 1.10 2001/07/09 16:27:50 boninfan Exp $
  +;;;       $Id: regions.lisp,v 1.11 2001/07/12 15:17:31 gilbert Exp $
   ;;; --------------------------------------------------------------------------------------
   ;;;  (c) copyright 1998,1999 by Gilbert Baumann
   ;;;  (c) copyright 2001 by Arnaud Rouanet (rouanet@emi.u-bordeaux.fr)
  
positive.code: 
  ;;;  When        Who    What
  ;;; --------------------------------------------------------------------------------------
  ;;;  2001-03-09  AR     fixed a bug in MAKE-ELLIPICAL-THING
  ;;;                     fixed STANDARD-ELLIPTICAL-ARC defclass
  ;;;  2001-03-06  AR     fixed bug in (REGION-EQUAL STANDARD-RECTANGLE STANDARD-RECTANGLE)
  ;;;                     REGION is now a subclass of DESIGN.
  ;;;  2001-01-21  GB     fixed bug in (TRANSFORM-REGION T RECTANGLE-SET)
  ;;;                     added some documentation
  ;;;  2001-07-09  GB     maybe fixed a bug in MAP-OVER-SCHNITT-GERADE/POLYGON.
  
  ;;; ---- TODO ----------------------------------------------------------------------------
  
  
negative.code:   ;; kill+yank alert
    (let (bx1 by1 bx2 by2)
      (map-over-region-set-regions (lambda (r)
                                     (multiple-value-bind (x1 y1 x2 y2) (bounding-rectangle* r)
                                       (setf bx1 (min (or bx1 x1) x1)
                                             bx2 (max (or bx2 x2) x2)
                                             by1 (min (or by1 y1) y1)
  