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    interface Accountable
    {
        const ERR_MSG = "error";
        public function isLoggedIn();
        public function getAccount($user = '');
    }
    abstract class Authentication implements Accountable
    {
        private $account = null;
        public function getAccount($user = '')
        {
            if ($this->account != null) {
                return $this->account;
            } else {
                return ERR_MSG;
            }
        }
        public function isLoggedIn()
        {
            return ($this->account != null);
        }
    }
    class