anchor.diff:          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)) )
  +        end-angle (and end-angle (coerce end-angle 'coordinate)) )
   
     (let ((tr (make-3-point-transformation* 0 0 1 0 0 1
                                             center-x center-y
  
positive.code:    (tr          :initarg :tr)))         ;a transformation from the unit circle to get the elliptical object
  
  (defclass standard-ellipse (ellipse elliptical-thing) ())
  (defclass standard-elliptical-arc (ellipse elliptical-thing) ())
  
  (defun ellipsep (object)
    (typep object 'ellipse))
  
negative.code: 
  (defmethod region-equal ((a standard-rectangle) (b standard-rectangle))
    (multiple-value-bind (x1 y1 x2 y2) (rectangle-edges* a)
      (multiple-value-bind (u1 v1 u2 v2) (rectangle-edges* b)
        (and (coordinate= x1 u1)
             (coordinate= y1 v1)
             (coordinate= x2 u2)
  