anchor.diff:  
   -behaviour(gen_server).
   
  --export([start/0, get_client/1, get_client_by_cookie/1]).
  +-export([start/0, get_client/1, get_client_by_cookie/1, create_table/0]).
   
   %% gen_server callbacks
   -export([init/1, handle_call/3, handle_cast/2, handle_info/2,
  
positive.code: 
  % id is Id -> {Client, Cookie}
  % cookie is Cookie -> Id
  -record(state, {id, cookie}).
  
  % Public:
  start() ->
  
negative.code:     {ok, Client} -> {reply, {ok, Client}, State};
      error -> {reply, {error, invalid}, State}
    end;
  
  handle_call({create_table}, From, State) ->
    NextId = State#state.table_cnt + 1,
    {ok, NewTable} = table:start(From),
    Tables1 = [NewTable|State#state.tables],
    {reply, {ok, NewTable, NextId}, State#state{tables=Tables1, table_cnt=NextId}};
  
  handle_call(Request, _From, State) ->
    io:format("~w received unknown call ~p~n",
  