anchor.diff:  
   ;;;  When        Who    What
   ;;; --------------------------------------------------------------------------------------
  +;;;  2001-07-12  GB     fixed bugs in
  +;;;                     (BOUNDING-RECTANGLE* STANDARD-REGION-UNION)
  +;;;                     (BOUNDING-RECTANGLE* STANDARD-REGION-INTERSECTION)
  +;;;  2001-07-09  GB     maybe fixed a bug in MAP-OVER-SCHNITT-GERADE/POLYGON.
   ;;;  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 ----------------------------------------------------------------------------
   
  
positive.code:   ;; kill+yank alert
    (let (bx1 by1 bx2 by2)
      (map-over-region-set-regions (lambda (r)
                                     (with-slots (x1 y1 x2 y2) r
                                       (setf bx1 (min (or bx1 x1) x1)
                                             bx2 (max (or bx2 x2) x2)
                                             by1 (min (or by1 y1) y1)
  
negative.code: (defmethod bounding-rectangle* ((self standard-region-union))
    (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)
  