anchor.diff:  ;;; Drawing datum LEXICAL-LOCATION.
   
   (defmethod draw-datum ((datum special-location) stream)
  +  (format stream "  ~a [shape = ellipse, style = filled];~%"
  +	  (datum-id datum))
     (format stream "   ~a [fillcolor = cyan4, label = \"~a\"]~%"
   	  (datum-id datum) (name datum)))
   
  
positive.code: ;;; Drawing datum EXTERNAL-INPUT.
  
  (defmethod draw-datum ((datum external-input) stream)
    (format stream "   ~a [fillcolor = pink, label = \"~a\"]~%"
  	  (datum-id datum) (value datum)))
  
  
negative.code: ;;; Drawing datum STATIC-LOCATION.
  
  (defmethod draw-datum ((datum static-location) stream)
    (format stream "  ~a [shape = ellipse, style = filled];~%"
  	  (datum-id datum))
    (format stream "   ~a [fillcolor = yellow, label = \"~a,~a\"]~%"
  	  (datum-id datum)
  	  (layer datum)
  