anchor.diff:      Pid = start_session(ID),
       ok = set_session_for_id(ID,Pid),
       {reply, {ok, Pid}, State};
  +handle_call({delete_session,ID}, _From, State) ->
  +    {ok, Pid} = lookup_session_pid(ID),
  +    delete_session(ID),
  +    tts_session:close(Pid),
  +    {reply, ok, State};
   handle_call(_Request, _From, State) ->
   	{reply, ignored, State}.
   
  
positive.code: 
  -export([new_session/0]).
  -export([get_session/1]).
  -export([session_closing/1]).
  %% gen_server.
  -export([init/1]).
  -export([handle_call/3]).
  
negative.code: get_session(ID) ->
      lookup_or_create_session_pid(ID).
  
  -spec session_wants_to_close(ID :: binary()) -> ok.
  session_wants_to_close(ID) ->
      gen_server:call(?MODULE,{delete_session,ID}).
  
  %% gen_server.
  
  