anchor.diff:  
   (defmethod stream-draw-ast ((ast return-from-ast) stream)
     (format stream "   ~a [label = \"return-from\"];~%"
  -	  (id ast))
  -  (format stream "   ~a -> ~a~%"
  -	  (id ast)
  -	  (id (block-ast ast)))
  -  (stream-draw-ast (form-ast ast) stream)
  -  (format stream "   ~a -> ~a~%"
  -	  (id ast)
  -	  (id (form-ast ast))))
  +	  (id ast)))
     
   (defmethod block-ast ((ast return-from-ast))
     (first (children ast)))
  
positive.code: (defmethod stream-draw-ast ((ast arg-ast) stream)
    (format stream "   ~a [style = filled, fillcolor = orange];~%" (id ast))
    (format stream "   ~a [label = \"arg\"];~%"
  	  (id ast))
    (stream-draw-ast (index-ast ast) stream)
    (format stream "   ~a -> ~a~%" (id ast) (id (index-ast ast))))
  
  (defmethod index-ast ((ast arg-ast))
    (first (children ast)))
  
negative.code: 
  (defmethod stream-draw-ast ((ast load-class-ast) stream)
    (format stream "   ~a [label = \"load-class\"];~%"
  	  (id ast)))
  
  (defmethod form-ast ((ast load-class-ast))
    (first (children ast)))
  