public static function exists() : bool
    {
        // Start session if needed
        if (! session_id()) {
            Session::start();
        }

        // Loop all arguments
        foreach (func_get_args() as $argument) {

            // Array element
            if (is_array($argument)) {

                // Loop the keys
                foreach ($argument as $key) {

                    // Does NOT exist
                    if (! isset($_SESSION[(string) $key])) {
                        return false;
                    }
                }
            } else {

                // Does NOT exist
                if (! isset($_SESSION[(string) $argument])) {
                    return false;
                }
            }
        }

        return true;
    }