anchor.diff:  (defmethod draw-datum :around (datum stream)
     (when (null (datum-id datum))
       (setf (gethash datum *datum-table*) (gensym))
  -    (format stream "  ~a [shape = ellipse, style = filled];~%"
  -	    (datum-id datum))
       (call-next-method)))
   
   ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  
positive.code: ;;; Drawing datum WORD-INPUT.
  
  (defmethod draw-datum ((datum word-input) stream)
    (format stream "   ~a [fillcolor = lightblue, label = \"~a\"]~%"
  	  (datum-id datum) (value datum)))
  
  
negative.code: ;;; Drawing datum DYNAMIC-LOCATION.
  
  (defmethod draw-datum ((datum dynamic-location) stream)
    (format stream "  ~a [shape = ellipse, style = filled];~%"
  	  (datum-id datum))
    (format stream "   ~a [fillcolor = darkorchid, label = \"~a\"]~%"
  	  (datum-id datum) (index datum)))
  
  