anchor.diff:  %
   mbox_test() ->
       D1 = dict:new(),
  +    M1 = #dmgr{curr = D1},
       A1 = mc_addr:local(),
  -    {D2, M1} = make_mbox(D1, A1),
  -    ?assertMatch({D2, M1}, make_mbox(D2, A1)).
  +    {M2, B1} = make_mbox(M1, A1),
  +    ?assertMatch({M2, B1}, make_mbox(M2, A1)).
   
  
positive.code: -compile(export_all).
  
  -record(mbox, {addr, pid, history}).
  
  %% API for downstream manager service.
  
  
negative.code: 
  %% gen_server implementation.
  
  init([]) -> {ok, #dmgr{curr = dict:new()}}.
  terminate(_Reason, _DMgr) -> ok.
  code_change(_OldVn, DMgr, _Extra) -> {ok, DMgr}.
  handle_info(_Info, DMgr) -> {noreply, DMgr}.
  handle_cast(_Msg, DMgr) -> {noreply, DMgr}.
  
  handle_call({monitor, Addr}, _From, DMgr) ->
      {DMgr2, #mbox{pid = Pid}} = make_mbox(DMgr, Addr),
      Reply = {ok, erlang:monitor(process, Pid)},
      {reply, Reply, DMgr2};
  handle_call({send, Addr, Op, NotifyPid,
               ResponseFun, CmdModule, Cmd, CmdArgs}, _From, DMgr) ->
      {DMgr2, #mbox{pid = Pid}} = make_mbox(DMgr, Addr),
      Pid ! {Op, NotifyPid, ResponseFun, CmdModule, Cmd, CmdArgs},
      {reply, ok, DMgr2}.
  
  % ---------------------------------------------------
  
  % Retrieves or creates an mbox for an Addr.
  make_mbox(#dmgr{curr = Dict} = DMgr, Addr) ->
      case dict:find(Addr, Dict) of
          {ok, MBox} -> {DMgr, MBox};
          _ -> MBox = create_mbox(Addr),
               Dict2 = dict:store(Addr, MBox, Dict),
               {#dmgr{curr = Dict2}, MBox}
      end.
  
  create_mbox(Addr) ->
  