(defgeneric update-system-for-new-interesting-object-predicate
    (system interesting-set uninteresting-set)
  (:documentation "Update bookkeeping in SYSTEM to accomodate changes in INTERESTING-OBJECT-P.
Both INTERESTING-SET and UNINTERESTING-SET can be a list of changed block statuses, or T if all known blocks should be reconsidered.
This is likely one of the longest symbols you will ever type.")
  (:method ((system standard-system))
    (dolistit ((set-name interesting-set uninteresting-set)
               (old-table (system-uninteresting-blocks system)
                          (system-interesting-blocks system))
               (new-table (system-interesting-blocks system)
                          (system-uninteresting-blocks system))
               (interesting-value t nil))
      (etypecase set-name
        (list (dolist (item set-name)
                (let ((info (gethash item old-table)))
                  (unless (null info)
                    (remhash item old-table)
                    (setf (gethash item new-table)
                          info)))))
        ((eql t) (loop for item being the hash-keys of old-name
                       for (version . channels) being the hash-values of old-name
                       when (eql (interesting-object-p system item version channels) interesting-value)
                         do (remhash item old-table)
                            (setf (gethash item new-table)
                                  (cons version channels))))))))