function add(string $name, string $namespace = '\\CismonX\\CaptchaQueue\\Rules') {
        if (isset($this->_formulaList[$name]))
            Console::warning("Overwriting formula \"$name\".");
        $class_name = $namespace . '\\' . $name;
        if (!class_exists($class_name)) {
            Console::warning("Invalid formula \"$name\".");
            return;
        }
        $this->_formulaList[$name] = new $class_name;
        self::enable($name);
    }