anchor.diff:      (values mxx mxy myx myy tx ty)))
   
   (defun make-translation-transformation (dx dy)
  -  (make-instance 'standard-translation
  -                 :dx (coordinate dx) :dy (coordinate dy)))
  +  (cond ((and (coordinate= dx 0) (coordinate= dy 0))
  +         +identity-transformation+)
  +        (t
  +         (make-instance 'standard-translation
  +                        :dx (coordinate dx) :dy (coordinate dy)))))
   
   (defun make-rotation-transformation (angle &optional origin)
     (if origin
  
positive.code: ;;;   Created: 1998-09-29
  ;;;    Author: Gilbert Baumann <unk6@rz.uni-karlsruhe.de>
  ;;;   License: LGPL (See file COPYING for details).
  ;;;       $Id: transforms.lisp,v 1.29 2005/02/02 10:18:58 tmoore Exp $
  ;;; --------------------------------------------------------------------------------------
  ;;;  (c) copyright 1998,1999,2003 by Gilbert Baumann
  ;;;  (c) copyright 2000 by 
  
negative.code:   ;; (compose-transformations A B)x = (A o B)x = ABx
    (with-slots ((dx1 dx) (dy1 dy)) transformation1
      (with-slots ((dx2 dx) (dy2 dy)) transformation2
        (make-translation-transformation (+ dx1 dx2) (+ dy1 dy2)))))
  
  (defmethod compose-transformations (transformation2
                                      (transformation1 standard-identity-transformation))
  