anchor.diff:  
   %% API.
   -export([start_link/0]).
  +-export([stop/0]).
   
   -export([new_session/0]).
   -export([get_session/1]).
  
positive.code: handle_call(_Request, _From, State) ->
      {reply, ignored, State}.
  
  handle_cast(_Msg, State) ->
      {noreply, State}.
  
  
negative.code: start_link() ->
      gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).
  
  -spec stop() -> ok.
  stop() ->
      gen_server:cast(?MODULE, stop).
  
  -spec new_session() -> {ok, pid()}.
  new_session() ->
  