anchor.diff:  
   reset_receive_done([Event|Rest], #scheduler_state{use_receive_patterns = true}) ->
     NewSpecial =
  -    [patch_message_delivery(S, dict:new()) || S <- Event#event.special],
  +    [patch_message_delivery(S, empty_map()) || S <- Event#event.special],
     [Event#event{special = NewSpecial}|Rest];
   reset_receive_done(Done, _) ->
     Done.
   
   fix_receive_info(RevTraceOrEvents) ->
  -  fix_receive_info(RevTraceOrEvents, dict:new()).
  +  fix_receive_info(RevTraceOrEvents, empty_map()).
   
   fix_receive_info(RevTraceOrEvents, ReceiveInfoDict) ->
     fix_receive_info(RevTraceOrEvents, ReceiveInfoDict, []).
  
positive.code: empty_map() ->
    dict:new().
  
  is_empty_map(Map) ->
    dict:size(Map) =:= 0.
  
  clock_map_store(P, V, ClockMap) ->
    dict:store(P, V, ClockMap).
  
  lookup_clock(P, ClockMap) ->
    case dict:find(P, ClockMap) of
  
negative.code:       true -> independent;
        false -> IrreversibleClock
      end,
    BaseNewClockMap = map_store(state, StateClock, ClockMap),
    NewClockMap = map_store(Actor, HappenedBeforeClock, BaseNewClockMap),
    %% The HB clock should also be added to anything else stemming
    %% from the step (spawns, sends and deliveries)
    FinalClockMap =
  