constexpr S end() const;
constexpr bool empty() const;
constexpr make-unsigned-like-t<iter_difference_t<I>> size() const
requires (K == subrange_kind::sized);
constexpr subrange next(iter_difference_t<I> n = 1) const &
requires forward_iterator<I>;
constexpr subrange next(iter_difference_t<I> n = 1) &&;
constexpr subrange prev(iter_difference_t<I> n = 1) const
requires bidirectional_iterator<I>;
constexpr subrange& advance(iter_difference_t<I> n);