anchor.diff:  %% API
   -export([start_link/4, add_peers/2, uploaded_data/2, downloaded_data/2,
   	peer_interested/1, peer_not_interested/1, peer_choked/1,
  -	peer_unchoked/1, got_piece_from_peer/2, new_incoming_peer/2]).
  +	peer_unchoked/1, got_piece_from_peer/2, new_incoming_peer/2,
  +	seed/1]).
   
   %% gen_server callbacks
   -export([init/1, handle_call/3, handle_cast/2, handle_info/2,
  
positive.code: handle_cast({got_piece_from_peer, Index}, S) ->
      broadcast_have_message(Index, S),
      {noreply, S};
  handle_cast(_Msg, State) ->
      {noreply, State}.
  
  
negative.code: 
  new_incoming_peer(Pid, PeerId) ->
      gen_server:call(Pid, {new_incoming_peer, PeerId}).
  
  seed(Pid) ->
      gen_server:cast(Pid, seed).
  
  %%====================================================================
  %% gen_server callbacks
  