anchor.diff:        (gen-convereter newnode-easy-converter)
         (gen-convereter lostnode-easy-converter)
         (gen-convereter #'identity))))
  -
  -(defun newnode-p (node refmark lostmark)
  -  (or (atom node) (composed-of-newnodes-p node refmark lostmark)))
  -
  -(defun composed-of-newnodes-p (tree refmark lostmark)
  -  (reduce (lambda (acc node)
  -            (and acc
  -                 (cond ((atom node) t)
  -                       ((or (refnode-p node refmark) (lostnode-p node lostmark)) nil)
  -                       (t (composed-of-newnodes-p node refmark lostmark)))))
  -          tree
  -          :initial-value t))
  
positive.code: ;;; achieve a suite a certain consistensy, it is good to introduce a
  ;;; special data structure for new node, too.  Moreover, nodes can
  ;;; be expressed as a class.
  (defun apply-converters (diff base refmark lostmark newnode-converter lostnode-converter refnode-converter)
    (with-route (cur route) diff
      (cond ((refnode-p cur refmark)
             (funcall refnode-converter cur route
                      (retrieve-by-route base (route-normalize (drop cur)))))
            ((lostnode-p cur lostmark)
             (funcall lostnode-converter cur route
                      (retrieve-by-route base (route-normalize (drop cur)))))
            ((newnode-p cur refmark lostmark)
             (funcall newnode-converter cur route cur))
            (t next-level))))
  
  ;;; An easy-converter takes a codelet as its only argument.
  (defun apply-modifiednode-converters
  
negative.code:             (values it
                      (route-relation route (funcall it :home))
                      (funcall it :mark)))
             ((collect-partly-bookings route basebook :home)
              (values it :partly t))
             (t (values nil nil nil)))))
  
  (defun rdiff% (base modified allowed-distance newmark refmark lostmark citedmark)
    (let (basebook modbook)
      (labels ((booking-as-ref (cited node cont cur)
                 (multiple-value-bind (booking relation mark)
  