anchor.diff:  
   (defgeneric draw-instruction (instruction stream))
     
  +(defmethod draw-instruction ((instruction typeq-instruction) stream)
  +  (format stream "   ~a [label = \"typeq ~a\"];~%"
  +	  (unique-id instruction)
  +	  (value-type instruction)))
  +
   (defmethod draw-instruction :around (instruction stream)
     (when (null (unique-id instruction))
       (setf (gethash instruction *instruction-table*) (gensym))
  
positive.code: 
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  ;;;
  ;;; Drawing datum LINKAGE-LOCATION.
  
  (defmethod draw-datum ((datum linkage-location) stream)
    (format stream "   ~a [fillcolor = bisque, label = \"~a, ~a\"]~%"
  	  (gethash datum *datum-table*)
  	  (index datum)
  	  (name datum)))
  
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  ;;;
  ;;; Drawing instructions.
  
  (defparameter *instruction-table* nil)
  
negative.code: 
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  ;;;
  ;;; Draw instruction CATCH-INSTRUCTION.
  
  (defmethod draw-instruction ((instruction catch-instruction) stream)
  