anchor.diff:               (setf (value (entry node)) data)
                (let ((maybe-new-entry (add-entry history data)))
                  (push (setf node (make-node :entry maybe-new-entry
  -                                           :parent (current owner)))
  +                                           :parent (current owner)
  +                                           :history history))
                        (children (current owner)))))
            (let ((binding (gethash owner (bindings (current owner)))))
              (setf (forward-child binding) node))
  
positive.code:       (root (parent node))
        node))
  
  (defun make-node (&key parent entry) ; TODO: Useless?
    (make-instance 'node :parent parent :entry entry))
  
  (define-class binding ()
    ((forward-child  nil
  
negative.code:           (setf (last-access binding) (local-time:now))
            (setf (gethash owner (bindings node))
                  (make-instance 'binding))))
      (values history node)))
  
  (defmethod visit-all ((history history-tree) node)
  