anchor.diff:  
   loop({Next, Messages} = State) ->
       receive
  -	{send_message, Message} ->
  +	{send_message, Message, _from} ->
   	    Next ! {new_message, {Message, self()}},
   	    loop(State);
   	{new_message, {Message, Node}} when Node == self() ->
  
positive.code:     Node ! quit,
      {ok, noreply}.
  
  fetch_message(NodePid) ->
      NodePid ! {fetch_message, self()},
      receive
  	{reply, Message} ->
  	    Message
      end.
  
  spawn_nodes(0, 0, Nodes) ->
      Nodes;
  spawn_nodes(N, I, []) ->
      spawn_nodes(N - 1, I, [spawn_node(undefined)]);
  spawn_nodes(N, I, Nodes = [H|_]) ->
      Next = spawn_node(H),
      spawn_nodes(N -1, I, [Next|Nodes]).
  
  spawn_node(Args) ->
      spawn(?MODULE, init, [Args]).
  
  init(undefined) ->
      loop({undefined, []});
  
negative.code: send_message(M, M, _Node, _Message) ->
      {ok, noreply};
  send_message(M, I, Node, Message) ->
      Node ! {send_message, Message, self()},
      send_message(M, I + 1, Node, Message).
  