anchor.diff:  
   (defmethod instance-finalized-p ((instance finalizable-instance))
     (%instance-finalized-p instance))
  +
  +(defmethod (setf instance-finalized-p) (new-value
  +					(instance finalizable-instance))
  +  (setf (%instance-finalized-p instance)
  +	(when new-value t)))
  +
   
   (defmethod finalize :around ((instance finalizable-instance))
     (unless (instance-finalized-p instance)
  
positive.code: 
  
  (defmacro assert-not-finalized (instance &optional format-control
  					 &rest format-args)
    (with-gensyms (%instance)
      `(let (,%instance ,instance)
         (when (instance-finalized-p ,%instance)
  	 ,@(cond
  	     (format-control
  	      `(error 'simple-instance-finalized-error
  		      :instance ,%instance
  		      :format-control ,format-control
  		      :format-arguments (list ,@format-args)))
  	     (t
  	      `(error 'instance-finalized-error
  		      :instance ,%instance)))))))
  
  
  ;;; * FINALIZABLE-INSTANCE
  
negative.code: 
  
  (defgeneric instance-finalized-p (instance))
  
  (defgeneric (setf instance-finalized-p) (new-value instance))
  
  
  ;;; * Condition Protocol: INSTANCE-FINALIZED
  