anchor.diff:      update_btime(F).
   
   write_bitmap(F = #mfile{otime = OTime, name = File, bitmaps = BMPs}) ->
  -    case {maps:size(BMPs), filelib:last_modified(File ++ ".bitmap")} of
  +    case {btrie:size(BMPs), filelib:last_modified(File ++ ".bitmap")} of
           {0, _} ->
               F;
           {_, OTimeA} when OTimeA =< OTime ->
  
positive.code:     set_bitmap(R, I + 1, B1).
  
  get_bitmap(Pos, M = #mfile{bitmaps = BMPs}) ->
      case maps:find(Pos, BMPs) of
          {ok, B} ->
              {B, M};
          error ->
  
negative.code: 
  write_bitmap_(F = #mfile{size = Size, bitmaps = BMPs, name = File}) ->
      BSize = bitmap:bytes(Size),
      case btrie:to_list(BMPs) of
          [] ->
              F;
          Data ->
              Writes = [{P * BSize, Bin} || {<<P:32>>, Bin} <- Data],
              {ok, IO} = file:open(File ++ ".bitmap", [raw, binary, write]),
              ok = file:pwrite(IO, Writes),
              ok = file:close(IO),
  