anchor.diff:                        NextKey, {?send_to_group_member, routing_table, Msg});
                   _ -> ok
               end,
  -            NewRT;
  -        _ -> RT
  +            Changed = (Index =:= first_index() orelse
  +                          (gb_trees:lookup(prev_index(Index), RT) =/= {value, Node})),
  +            {gb_trees:enter(Index, Node, RT), Changed};
  +        _ ->
  +            {RT, false}
       end.
   %% userdevguide-end rt_chord:stabilize
   
  
positive.code: -spec check(OldRT::rt(), NewRT::rt(), OldNeighbors::nodelist:neighborhood(),
              NewNeighbors::nodelist:neighborhood(), ReportToFD::boolean()) -> ok.
  check(OldRT, NewRT, OldNeighbors, NewNeighbors, ReportToFD) ->
      case OldRT =:= NewRT andalso
               nodelist:pred(OldNeighbors) =:= nodelist:pred(NewNeighbors) andalso
               nodelist:succ(OldNeighbors) =:= nodelist:succ(NewNeighbors) of
          true -> ok;
          _ ->
              Pid = pid_groups:get_my(dht_node),
              RT_ext = export_rt_to_dht_node(NewRT, NewNeighbors),
              case Pid of
                  failed -> ok;
                  _      -> comm:send_local(Pid, {rt_update, RT_ext})
              end,
              % update failure detector:
              case ReportToFD of
                  true ->
                      NewPids = to_pid_list(NewRT),
                      OldPids = to_pid_list(OldRT),
                      fd:update_subscriptions(OldPids, NewPids);
                  _ -> ok
              end
      end.
  %% userdevguide-end rt_chord:check
  
  
negative.code: %%      Provided for convenience (see check/5).
  -spec check(OldRT::rt(), NewRT::rt(), Neighbors::nodelist:neighborhood(),
              ReportToFD::boolean()) -> ok.
  check(OldRT, OldRT, _Neighbors, _ReportToFD) ->
      ok;
  check(OldRT, NewRT, Neighbors, ReportToFD) ->
      check_do_update(OldRT, NewRT, Neighbors, ReportToFD).
  
  %% @doc Notifies the dht_node if the (external) routing table changed.
  %%      Also updates the failure detector if ReportToFD is set.
  