namespace boost {
  namespace text {
    struct null_sentinel_t;
    struct throw_logic_error;
    struct use_replacement_character;
    template<typename Cont> struct utf_16_to_32_back_insert_iterator;
    template<typename Cont> struct utf_16_to_32_front_insert_iterator;
    template<typename Cont> struct utf_16_to_32_insert_iterator;
    template<utf16_iter I, std::sentinel_for< I > S = I, 
             transcoding_error_handler ErrorHandler = use_replacement_character> 
      struct utf_16_to_32_iterator;
    template<std::output_iterator< uint32_t > Iter> 
      struct utf_16_to_32_out_iterator;
    template<typename Cont> struct utf_16_to_8_back_insert_iterator;
    template<typename Cont> struct utf_16_to_8_front_insert_iterator;
    template<typename Cont> struct utf_16_to_8_insert_iterator;
    template<utf16_iter I, std::sentinel_for< I > S = I, 
             transcoding_error_handler ErrorHandler = use_replacement_character> 
      struct utf_16_to_8_iterator;
    template<std::output_iterator< uint8_t > Iter> 
      struct utf_16_to_8_out_iterator;
    template<typename Cont> struct utf_32_to_16_back_insert_iterator;
    template<typename Cont> struct utf_32_to_16_front_insert_iterator;
    template<typename Cont> struct utf_32_to_16_insert_iterator;
    template<utf32_iter I, std::sentinel_for< I > S = I, 
             transcoding_error_handler ErrorHandler = use_replacement_character> 
      struct utf_32_to_16_iterator;
    template<std::output_iterator< uint16_t > Iter> 
      struct utf_32_to_16_out_iterator;
    template<typename Cont> struct utf_32_to_8_back_insert_iterator;
    template<typename Cont> struct utf_32_to_8_front_insert_iterator;
    template<typename Cont> struct utf_32_to_8_insert_iterator;
    template<utf32_iter I, std::sentinel_for< I > S = I, 
             transcoding_error_handler ErrorHandler = use_replacement_character> 
      struct utf_32_to_8_iterator;
    template<std::output_iterator< uint8_t > Iter> 
      struct utf_32_to_8_out_iterator;
    template<typename Cont> struct utf_8_to_16_back_insert_iterator;
    template<typename Cont> struct utf_8_to_16_front_insert_iterator;
    template<typename Cont> struct utf_8_to_16_insert_iterator;
    template<utf8_iter I, std::sentinel_for< I > S, 
             transcoding_error_handler ErrorHandler> 
      struct utf_8_to_16_iterator;
    template<std::output_iterator< uint16_t > Iter> 
      struct utf_8_to_16_out_iterator;
    template<typename Cont> struct utf_8_to_32_back_insert_iterator;
    template<typename Cont> struct utf_8_to_32_front_insert_iterator;
    template<typename Cont> struct utf_8_to_32_insert_iterator;
    template<utf8_iter I, std::sentinel_for< I > S = I, 
             transcoding_error_handler ErrorHandler = use_replacement_character> 
      struct utf_8_to_32_iterator;
    template<std::output_iterator< uint32_t > Iter> 
      struct utf_8_to_32_out_iterator;
    constexpr uint32_t replacement_character();
    constexpr bool surrogate(uint32_t);
    constexpr bool high_surrogate(uint32_t);
    constexpr bool low_surrogate(uint32_t);
    constexpr bool reserved_noncharacter(uint32_t);
    constexpr bool scalar_value(uint32_t);
    constexpr bool unreserved_scalar_value(uint32_t);
    constexpr bool lead_code_unit(unsigned char);
    constexpr bool continuation(unsigned char);
    constexpr int utf8_code_units(unsigned char);
    constexpr int utf16_code_units(uint16_t);
    template<typename T> constexpr auto operator==(T * p, null_sentinel_t);
    template<typename T> constexpr auto operator!=(T * p, null_sentinel_t);
    template<typename T> constexpr auto operator==(null_sentinel_t, T * p);
    template<typename T> constexpr auto operator!=(null_sentinel_t, T * p);
    template<typename Iter, typename Sentinel, typename ErrorHandler> 
      constexpr auto 
      operator==(utf_32_to_8_iterator< Iter, Sentinel, ErrorHandler > const & lhs, 
                 Sentinel rhs);
    template<typename Iter, typename Sentinel, typename ErrorHandler> 
      constexpr auto 
      operator==(Sentinel lhs, 
                 utf_32_to_8_iterator< Iter, Sentinel, ErrorHandler > const & rhs);
    template<typename Iter, typename Sentinel, typename ErrorHandler> 
      constexpr auto 
      operator!=(utf_32_to_8_iterator< Iter, Sentinel, ErrorHandler > const & lhs, 
                 Sentinel rhs);
    template<typename Iter, typename Sentinel, typename ErrorHandler> 
      constexpr auto 
      operator!=(Sentinel lhs, 
                 utf_32_to_8_iterator< Iter, Sentinel, ErrorHandler > const & rhs);
    template<typename Iter1, typename Sentinel1, typename Iter2, 
             typename Sentinel2, typename ErrorHandler> 
      constexpr auto 
      operator==(utf_32_to_8_iterator< Iter1, Sentinel1, ErrorHandler > const & lhs, 
                 utf_32_to_8_iterator< Iter2, Sentinel2, ErrorHandler > const & rhs);
    template<typename Iter1, typename Sentinel1, typename Iter2, 
             typename Sentinel2, typename ErrorHandler> 
      constexpr auto 
      operator!=(utf_32_to_8_iterator< Iter1, Sentinel1, ErrorHandler > const & lhs, 
                 utf_32_to_8_iterator< Iter2, Sentinel2, ErrorHandler > const & rhs);
    template<typename Iter, typename Sentinel, typename ErrorHandler> 
      constexpr auto 
      operator==(utf_8_to_32_iterator< Iter, Sentinel, ErrorHandler > const & lhs, 
                 Sentinel rhs);
    template<typename Iter, typename Sentinel, typename ErrorHandler> 
      constexpr auto 
      operator==(Sentinel lhs, 
                 utf_8_to_32_iterator< Iter, Sentinel, ErrorHandler > const & rhs);
    template<typename Iter, typename Sentinel, typename ErrorHandler> 
      constexpr auto 
      operator!=(utf_8_to_32_iterator< Iter, Sentinel, ErrorHandler > const & lhs, 
                 Sentinel rhs);
    template<typename Iter, typename Sentinel, typename ErrorHandler> 
      constexpr auto 
      operator!=(Sentinel lhs, 
                 utf_8_to_32_iterator< Iter, Sentinel, ErrorHandler > const & rhs);
    template<typename Iter1, typename Sentinel1, typename Iter2, 
             typename Sentinel2, typename ErrorHandler> 
      constexpr auto 
      operator==(utf_8_to_32_iterator< Iter1, Sentinel1, ErrorHandler > const & lhs, 
                 utf_8_to_32_iterator< Iter2, Sentinel2, ErrorHandler > const & rhs);
    template<typename Iter1, typename Sentinel1, typename Iter2, 
             typename Sentinel2, typename ErrorHandler> 
      constexpr auto 
      operator!=(utf_8_to_32_iterator< Iter1, Sentinel1, ErrorHandler > const & lhs, 
                 utf_8_to_32_iterator< Iter2, Sentinel2, ErrorHandler > const & rhs);
    template<typename Iter, typename Sentinel, typename ErrorHandler> 
      constexpr auto 
      operator==(utf_32_to_16_iterator< Iter, Sentinel, ErrorHandler > const & lhs, 
                 Sentinel rhs);
    template<typename Iter, typename Sentinel, typename ErrorHandler> 
      constexpr auto 
      operator==(Sentinel lhs, 
                 utf_32_to_16_iterator< Iter, Sentinel, ErrorHandler > const & rhs);
    template<typename Iter, typename Sentinel, typename ErrorHandler> 
      constexpr auto 
      operator!=(utf_32_to_16_iterator< Iter, Sentinel, ErrorHandler > const & lhs, 
                 Sentinel rhs);
    template<typename Iter, typename Sentinel, typename ErrorHandler> 
      constexpr auto 
      operator!=(Sentinel lhs, 
                 utf_32_to_16_iterator< Iter, Sentinel, ErrorHandler > const & rhs);
    template<typename Iter1, typename Sentinel1, typename Iter2, 
             typename Sentinel2, typename ErrorHandler> 
      constexpr auto 
      operator==(utf_32_to_16_iterator< Iter1, Sentinel1, ErrorHandler > const & lhs, 
                 utf_32_to_16_iterator< Iter2, Sentinel2, ErrorHandler > const & rhs);
    template<typename Iter1, typename Sentinel1, typename Iter2, 
             typename Sentinel2, typename ErrorHandler> 
      constexpr auto 
      operator!=(utf_32_to_16_iterator< Iter1, Sentinel1, ErrorHandler > const & lhs, 
                 utf_32_to_16_iterator< Iter2, Sentinel2, ErrorHandler > const & rhs);
    template<typename Iter, typename Sentinel, typename ErrorHandler> 
      constexpr auto 
      operator==(utf_16_to_32_iterator< Iter, Sentinel, ErrorHandler > const & lhs, 
                 Sentinel rhs);
    template<typename Iter, typename Sentinel, typename ErrorHandler> 
      constexpr auto 
      operator==(Sentinel lhs, 
                 utf_16_to_32_iterator< Iter, Sentinel, ErrorHandler > const & rhs);
    template<typename Iter, typename Sentinel, typename ErrorHandler> 
      constexpr auto 
      operator!=(utf_16_to_32_iterator< Iter, Sentinel, ErrorHandler > const & lhs, 
                 Sentinel rhs);
    template<typename Iter, typename Sentinel, typename ErrorHandler> 
      constexpr auto 
      operator!=(Sentinel lhs, 
                 utf_16_to_32_iterator< Iter, Sentinel, ErrorHandler > const & rhs);
    template<typename Iter1, typename Sentinel1, typename Iter2, 
             typename Sentinel2, typename ErrorHandler> 
      constexpr auto 
      operator==(utf_16_to_32_iterator< Iter1, Sentinel1, ErrorHandler > const & lhs, 
                 utf_16_to_32_iterator< Iter2, Sentinel2, ErrorHandler > const & rhs);
    template<typename Iter1, typename Sentinel1, typename Iter2, 
             typename Sentinel2, typename ErrorHandler> 
      constexpr auto 
      operator!=(utf_16_to_32_iterator< Iter1, Sentinel1, ErrorHandler > const & lhs, 
                 utf_16_to_32_iterator< Iter2, Sentinel2, ErrorHandler > const & rhs);
    template<typename Iter, typename Sentinel, typename ErrorHandler> 
      constexpr auto 
      operator==(utf_16_to_8_iterator< Iter, Sentinel, ErrorHandler > const & lhs, 
                 Sentinel rhs);
    template<typename Iter, typename Sentinel, typename ErrorHandler> 
      constexpr auto 
      operator==(Sentinel lhs, 
                 utf_16_to_8_iterator< Iter, Sentinel, ErrorHandler > const & rhs);
    template<typename Iter, typename Sentinel, typename ErrorHandler> 
      constexpr auto 
      operator!=(utf_16_to_8_iterator< Iter, Sentinel, ErrorHandler > const & lhs, 
                 Sentinel rhs);
    template<typename Iter, typename Sentinel, typename ErrorHandler> 
      constexpr auto 
      operator!=(Sentinel lhs, 
                 utf_16_to_8_iterator< Iter, Sentinel, ErrorHandler > const & rhs);
    template<typename Iter1, typename Sentinel1, typename Iter2, 
             typename Sentinel2, typename ErrorHandler> 
      constexpr auto 
      operator==(utf_16_to_8_iterator< Iter1, Sentinel1, ErrorHandler > const & lhs, 
                 utf_16_to_8_iterator< Iter2, Sentinel2, ErrorHandler > const & rhs);
    template<typename Iter1, typename Sentinel1, typename Iter2, 
             typename Sentinel2, typename ErrorHandler> 
      constexpr auto 
      operator!=(utf_16_to_8_iterator< Iter1, Sentinel1, ErrorHandler > const & lhs, 
                 utf_16_to_8_iterator< Iter2, Sentinel2, ErrorHandler > const & rhs);
    template<typename Iter, typename Sentinel, typename ErrorHandler> 
      constexpr auto 
      operator==(utf_8_to_16_iterator< Iter, Sentinel, ErrorHandler > const & lhs, 
                 Sentinel rhs);
    template<typename Iter, typename Sentinel, typename ErrorHandler> 
      constexpr auto 
      operator==(Sentinel lhs, 
                 utf_8_to_16_iterator< Iter, Sentinel, ErrorHandler > const & rhs);
    template<typename Iter, typename Sentinel, typename ErrorHandler> 
      constexpr auto 
      operator!=(utf_8_to_16_iterator< Iter, Sentinel, ErrorHandler > const & lhs, 
                 Sentinel rhs);
    template<typename Iter, typename Sentinel, typename ErrorHandler> 
      constexpr auto 
      operator!=(Sentinel lhs, 
                 utf_8_to_16_iterator< Iter, Sentinel, ErrorHandler > const & rhs);
    template<typename Iter1, typename Sentinel1, typename Iter2, 
             typename Sentinel2, typename ErrorHandler> 
      constexpr auto 
      operator==(utf_8_to_16_iterator< Iter1, Sentinel1, ErrorHandler > const & lhs, 
                 utf_8_to_16_iterator< Iter2, Sentinel2, ErrorHandler > const & rhs);
    template<typename Iter1, typename Sentinel1, typename Iter2, 
             typename Sentinel2, typename ErrorHandler> 
      constexpr auto 
      operator!=(utf_8_to_16_iterator< Iter1, Sentinel1, ErrorHandler > const & lhs, 
                 utf_8_to_16_iterator< Iter2, Sentinel2, ErrorHandler > const & rhs);
    namespace v1 {
      template<utf8_iter I> constexpr I find_invalid_encoding(I, I);
      template<utf8_iter I> constexpr bool encoded(I, I);
      template<utf8_iter I> constexpr bool starts_encoded(I, I);
      template<utf8_iter I> constexpr bool ends_encoded(I, I);
      template<typename Iter> 
        unspecified find_invalid_encoding(Iter first, Iter last);
      template<typename Iter> 
        unspecified find_invalid_encoding(Iter first, Iter last);
      template<typename Iter> unspecified encoded(Iter first, Iter last);
      template<typename Iter> unspecified encoded(Iter first, Iter last);
      template<typename Iter> 
        unspecified starts_encoded(Iter first, Iter last);
      template<typename Iter> 
        unspecified starts_encoded(Iter first, Iter last);
      template<typename Iter> unspecified ends_encoded(Iter first, Iter last);
      template<typename Iter> unspecified ends_encoded(Iter first, Iter last);
      template<std::output_iterator< uint8_t > O> 
        utf_32_to_8_out_iterator< O > utf_32_to_8_out(O);
      template<std::output_iterator< uint32_t > O> 
        utf_8_to_32_out_iterator< O > utf_8_to_32_out(O);
      template<std::output_iterator< uint16_t > O> 
        utf_32_to_16_out_iterator< O > utf_32_to_16_out(O);
      template<std::output_iterator< uint32_t > O> 
        utf_16_to_32_out_iterator< O > utf_16_to_32_out(O);
      template<std::output_iterator< uint8_t > O> 
        utf_16_to_8_out_iterator< O > utf_16_to_8_out(O);
      template<std::output_iterator< uint16_t > O> 
        utf_8_to_16_out_iterator< O > utf_8_to_16_out(O);
      template<std::bidirectional_iterator I, std::sentinel_for< I > S> 
        auto utf8_iterator(I, I, S);
      template<std::bidirectional_iterator I, std::sentinel_for< I > S> 
        auto utf16_iterator(I, I, S);
      template<std::bidirectional_iterator I, std::sentinel_for< I > S> 
        auto utf32_iterator(I, I, S);
      template<typename Cont> 
        auto from_utf8_inserter(Cont &, typename Cont::iterator);
      template<typename Cont> 
        auto from_utf16_inserter(Cont &, typename Cont::iterator);
      template<typename Cont> 
        auto from_utf32_inserter(Cont &, typename Cont::iterator);
      template<typename Cont> auto from_utf8_back_inserter(Cont &);
      template<typename Cont> auto from_utf16_back_inserter(Cont &);
      template<typename Cont> auto from_utf32_back_inserter(Cont &);
      template<typename Cont> auto from_utf8_front_inserter(Cont &);
      template<typename Cont> auto from_utf16_front_inserter(Cont &);
      template<typename Cont> auto from_utf32_front_inserter(Cont &);
      template<typename Iter> 
        utf_32_to_8_out_iterator< Iter > utf_32_to_8_out(Iter it);
      template<typename Iter> 
        utf_8_to_32_out_iterator< Iter > utf_8_to_32_out(Iter it);
      template<typename Iter> 
        utf_32_to_16_out_iterator< Iter > utf_32_to_16_out(Iter it);
      template<typename Iter> 
        utf_16_to_32_out_iterator< Iter > utf_16_to_32_out(Iter it);
      template<typename Iter> 
        utf_16_to_8_out_iterator< Iter > utf_16_to_8_out(Iter it);
      template<typename Iter> 
        utf_8_to_16_out_iterator< Iter > utf_8_to_16_out(Iter it);
      template<typename Iter, typename Sentinel> 
        auto utf8_iterator(Iter first, Iter it, Sentinel last);
      template<typename Iter, typename Sentinel> 
        auto utf16_iterator(Iter first, Iter it, Sentinel last);
      template<typename Iter, typename Sentinel> 
        auto utf32_iterator(Iter first, Iter it, Sentinel last);
      template<typename Cont> 
        auto from_utf8_inserter(Cont &, typename Cont::iterator);
      template<typename Cont> 
        auto from_utf16_inserter(Cont &, typename Cont::iterator);
      template<typename Cont> 
        auto from_utf32_inserter(Cont &, typename Cont::iterator);
      template<typename Cont> auto from_utf8_back_inserter(Cont &);
      template<typename Cont> auto from_utf16_back_inserter(Cont &);
      template<typename Cont> auto from_utf32_back_inserter(Cont &);
      template<typename Cont> auto from_utf8_front_inserter(Cont &);
      template<typename Cont> auto from_utf16_front_inserter(Cont &);
      template<typename Cont> auto from_utf32_front_inserter(Cont &);
    }
  }
}