anchor.diff:      #state{
           pieces_begun=Begun,
           pieces_assigned=Assigned,
  +        pieces_stored=Stored,
           chunks_assigned=AssignedChunks,
           peer_monitors=Peers} = State,
   
  
positive.code: %% Mark a chunk as fetched but not written to file.
  %% @end
  -spec mark_fetched(torrent_id(), pos_integer(),
                     pos_integer(), pos_integer()) -> {ok, list(pid())}.
  mark_fetched(TorrentID, Index, Offset, Length) ->
      ChunkSrv = lookup_chunk_server(TorrentID),
      call(ChunkSrv, {mark_fetched, self(), Index, Offset, Length}).
  
negative.code:         %% None that we are not already downloading
          %% and none that we would want to download
          {0, 0} ->
              Interesting = etorrent_pieceset:difference(Peerset, Stored),
              case etorrent_pieceset:size(Interesting) of
                  0 -> not_interested;
                  _ -> assigned
              end;
          %% None that we are not already downloading
          %% but one ore more that we would want to download
          {0, _} ->
  