namespace std {
template <class T> struct is_literal_type;
template <class T> constexpr bool is_literal_type_v = is_literal_type<T>::value;
template <class> struct result_of; // not defined
template <class Fn, class... ArgTypes> struct result_of<Fn(ArgTypes...)>;
template <class T> using result_of_t = typename result_of<T>::type;
}