constexpr explicit outer-iterator(Parent& parent)
requires (!forward_range<Base>);
constexpr outer-iterator(Parent& parent, iterator_t<Base> current)
requires forward_range<Base>;
constexpr outer-iterator(outer-iterator<!Const> i)
requires Const && convertible_to<iterator_t<V>, iterator_t<Base>>;
constexpr value_type operator*() const;
constexpr outer-iterator& operator++();
friend constexpr bool operator==(const outer-iterator& x, const outer-iterator& y)
requires forward_range<Base>;
friend constexpr bool operator==(const outer-iterator& x, default_sentinel_t);