anchor.diff:  handle_call({create,UserId}, _From, State) ->
       Result = create_new_user(UserId),
       {reply, Result, State};
  -handle_call({delet_user,ID}, _From, State) ->
  -    delete_user(ID),
  +handle_call({user_wants_to_shutdown,ID}, _From, State) ->
  +    {ok,Pid} = lookup_user(ID),
  +    true = delete_user(ID),
  +    ok = tts_user:shutdown(Pid),
       {reply, ok, State};
   handle_call(_Request, _From, State) ->
   	{reply, ignored, State}.
  
positive.code:     case add_new_user_entry(UserId,Pid) of
          ok -> 
              {ok, Pid};
          _ ->
              ok = tts_user:stop(Pid),
              lookup_user(UserMap)
      end.
  
negative.code: %% API.
  -export([start_link/0]).
  -export([get_user/2]).
  -export([user_wants_to_shutdown/1]).
  
  %% gen_server.
  -export([init/1]).
  