anchor.diff:  (defmethod scaling-transformation-p ((transformation standard-transformation))
     ;; Q: was ist mit dem translationsanteil?
     ;; what gives (scaling-transformation-p (make-translation-transformation 17 42))
  +  ;; I think it would be strange if (s-t-p (make-s-t* 2 1 1 0)) is not T. -- APD
     (multiple-value-bind (mxx mxy myx myy tx ty) (get-transformation transformation)
  -    (and (coordinate= 0 tx) (coordinate= 0 ty)
  -         (coordinate= 0 mxy) (coordinate= 0 myx)
  -         (coordinate/= 0 mxx) (coordinate/= 0 myy))))
  +    (and (coordinate= 0 mxy) (coordinate= 0 myx)
  +         (coordinate/= 0 mxx) (coordinate/= 0 myy)))) ; ?
   
   (defmethod rectilinear-transformation-p ((transformation standard-transformation))
     ;; Das testen wir einfach ganz brutal
     ;;; ist das auch richtig?
  -  (multiple-value-bind (dx1 dy1) (transform-distance transformation 1 0)
  -    (multiple-value-bind (dx2 dy2) (transform-distance transformation 0 1)
  -      (or (and (coordinate= dx1 0) (coordinate/= dy1 0)
  -               (coordinate/= dx2 0) (coordinate= dy2 0))
  -          (and (coordinate/= dx1 0) (coordinate= dy1 0)
  -               (coordinate= dx2 0) (coordinate/= dy2 0))))))
  +  (multiple-value-bind (mxx mxy myx myy) (get-transformation transformation)
  +    (or (and (coordinate= mxx 0) (coordinate/= mxy 0)
  +             (coordinate/= myx 0) (coordinate= myy 0))
  +        (and (coordinate/= mxx 0) (coordinate= mxy 0)
  +             (coordinate= myx 0) (coordinate/= myy 0)))))
   
   (defmethod y-inverting-transformation-p ((transformation standard-transformation))
     (multiple-value-bind (mxx mxy myx myy) (get-transformation transformation)
  
positive.code:          (coordinate= myx 0)
           (coordinate= myy 1))))
  
  (defmethod invertible-transformation-p ((transformation standard-transformation))
    (coordinate/= 0 (transformation-determinant transformation)))
  
  (defun transformation-determinant (tr)
    (multiple-value-bind (mxx mxy myx myy) (get-transformation tr)
      (- (* mxx myy) (* mxy myx))))
  
  (defmethod reflection-transformation-p ((transformation standard-transformation))
    (< (transformation-determinant transformation) 0))
  
negative.code: 		     (transformation-error-rect self)
  		     (transformation-error-transformation self)))))
  
  (defmethod transformation-equal ((transformation1 standard-transformation)
                                   (transformation2 standard-transformation))
    (every #'coordinate=
           (multiple-value-list (get-transformation transformation1))
           (multiple-value-list (get-transformation transformation2))))
  
  (defmethod identity-transformation-p ((transformation standard-transformation))
    (transformation-equal transformation +identity-transformation+))
  
  