anchor.diff:  -export([init/1, handle_call/3, handle_cast/2, handle_info/2,
            terminate/2, code_change/3]).
   
  --define(SERVER, ?MODULE). 
  +-define(SERVER, ?MODULE).
   
   -record(state, {left = nil, value, right = nil}).
   
  
positive.code: %%%-------------------------------------------------------------------
  %%% @author  <>
  %%% @copyright (C) 2013, 
  %%% @doc
  %%%
  %%% @end
  
negative.code:                     {reply, added, State#state{right=NewPid}};
                  true ->
                      gen_server:call(Right, {add, Data}),
                      {reply, added, State}
              end
      end;
  
  