anchor.diff:      end.
   
   notify(P, D, V) when is_pid(P) -> P ! {D, V};
  -notify(_, _, _) -> ok.
  +notify(_, _, _)                -> ok.
   
   group_by(Keys, KeyFunc) ->
       group_by(Keys, KeyFunc, dict:new()).
  
positive.code:     end.
  
  await_ok(N) -> await_ok(undefined, N, 0).
  await_ok(NotifyData, N, Acc) when N > 0 ->
      % TODO: Decrementing N due to a DOWN might be incorrect
      % during edge/race conditions.
      receive
          {NotifyData, {ok, _}}    -> await_ok(NotifyData, N - 1, Acc + 1);
          {NotifyData, {ok, _, _}} -> await_ok(NotifyData, N - 1, Acc + 1);
          {'DOWN', _MonitorRef, _, _, _}  -> await_ok(NotifyData, N - 1, Acc);
          Unexpected -> ?debugVal(Unexpected),
                        exit({error, Unexpected})
      end;
  await_ok(_, _, Acc) -> Acc.
  
  
negative.code: 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) ->
  