anchor.diff:        {system_communication, _} ->
           Actors
       end,
  -  NewNext = Next#trace_state{actors = NewActors},
  -  State#scheduler_state{trace = [NewNext|Trace]}.
  +  TraceState#trace_state{actors = NewActors}.
   
   add_message(MessageEvent, Actors) ->
     #message_event{recipient = Recipient, sender = Sender} = MessageEvent,
  
positive.code:     end,
    lists:filter(Pred, Sleeping).
  
  update_special(List, State) when is_list(List) ->
    lists:foldl(fun update_special/2, State, List);
  update_special(Special, State) ->
    #scheduler_state{trace = [#trace_state{actors = Actors} = Next|Trace]} = State,
    NewActors =
      case Special of
        halt -> [];
  
negative.code:       done = NewLastDone,
        wakeup_tree = NewLastWakeupTree
       },
    NextTrace = update_special(Event#event.special, InitNextTrace),
    InitNewState =
      State#scheduler_state{trace = [NextTrace, NewLastTrace|Prev]},
    NewState = maybe_log(Event, InitNewState, Index),
    {ok, NewState}.
  
  maybe_log(#event{actor = P} = Event, State0, Index) ->
    #scheduler_state{
  