anchor.diff:    t)
   
   (defmethod transformation-equal ((t1 standard-identity-transformation)
  -                                 (t2 t))
  +                                 (t2 transformation))
     nil)
   
  -(defmethod transformation-equal ((t2 t)
  +(defmethod transformation-equal ((t2 transformation)
                                    (t1 standard-identity-transformation))
     nil)
   
  
positive.code:            (coordinate= dy1 dy2)))))
  
  (defmethod transformation-equal ((t1 standard-translation)
                                   (t2 t))
    nil)
  
  (defmethod transformation-equal ((t2 t)
                                   (t1 standard-translation))
    nil)
  
negative.code:       (make-translation-transformation (+ dx1 dx2) (+ dy1 dy2)))))
  
  (defmethod compose-transformations
      ((transformation2 transformation) (transformation1 standard-identity-transformation))
    transformation2)
  
  (defmethod compose-transformations
      ((transformation2 standard-identity-transformation) (transformation1 transformation))
    transformation1)
  
  (defmethod invert-transformation
  