anchor.diff:  ;;; --------------------------------------------------------------------------------------
   ;;;  2001-01-21  GB     fixed bug in (TRANSFORM-REGION T RECTANGLE-SET)
   ;;;                     added some documentation
  +;;;  2001-03-06  AR     fixed bug in (REGION-EQUAL STANDARD-RECTANGLE STANDARD-RECTANGLE)
  +;;;                     REGION is now a subclass of DESIGN.
  +;;;  2001-03-09  AR     fixed a bug in MAKE-ELLIPICAL-THING
  +;;;                     fixed STANDARD-ELLIPTICAL-ARC defclass
   
   ;;; ---- TODO ----------------------------------------------------------------------------
   
  
positive.code:         radius-2-dx (coerce radius-2-dx 'coordinate)
          radius-2-dy (coerce radius-2-dy 'coordinate)
          start-angle (and start-angle (coerce start-angle 'coordinate))
          end-angle (and start-angle (coerce start-angle 'coordinate)) )
  
    (let ((tr (make-3-point-transformation* 0 0 1 0 0 1
                                            center-x center-y
  
negative.code: 
  (defclass bounding-rectangle () ())
  
  (defclass region (design) ())
  (defclass path (region bounding-rectangle) ())
  (defclass area (region bounding-rectangle) ())
  (defclass region-set  (region bounding-rectangle) ())
  