anchor.diff:  insert_message(Channel, Update, _Initial, [{Channel, Queue}|Rest], true, Acc) ->
     NewQueue = Update(Queue),
     lists:reverse(Acc, [{Channel, NewQueue}|Rest]);
  -insert_message({From, _} = Channel, Update, Initial, [Other|Rest], Found, Acc) ->
  +insert_message(Channel, Update, Initial, [Other|Rest], Found, Acc) ->
  +  {From, _} = Channel,
     case Other of
       {{_, _}, _} ->
         insert_message(Channel, Update, Initial, Rest, Found, [Other|Acc]);
  
positive.code:       ObsNewSpecial =
          case lists:keyfind(message_delivered, 1, NewSpecial) of
            {message_delivered, #message_event{message = #message{id = NewId}}} ->
              lists:keyreplace(ObserverInfo, 2, Special, {message_received, NewId});
            _ -> exit(impossible)
          end,
        [E#event{label = undefined, special = ObsNewSpecial}|NotObs]
  
negative.code: 
  %% =============================================================================
  
  reset_receive_done([Event|Rest], State)
    when State#scheduler_state.use_receive_patterns =:= true ->
    NewSpecial =
      [patch_message_delivery(S, empty_map()) || S <- Event#event.special],
    [Event#event{special = NewSpecial}|Rest];
  