constexpr bool operator==(const year& x, const year& y) noexcept;
constexpr strong_ordering operator<=>(const year& x, const year& y) noexcept;
constexpr year operator+(const year& x, const years& y) noexcept;
constexpr year operator+(const years& x, const year& y) noexcept;
constexpr year operator-(const year& x, const years& y) noexcept;
constexpr years operator-(const year& x, const year& y) noexcept;
template<class charT, class traits>
basic_ostream<charT, traits>&
operator<<(basic_ostream<charT, traits>& os, const year& y);
template<class charT, class traits, class Alloc = allocator<charT>>
basic_istream<charT, traits>&
from_stream(basic_istream<charT, traits>& is, const charT* fmt,
year& y, basic_string<charT, traits, Alloc>* abbrev = nullptr,
minutes* offset = nullptr);
constexpr chrono::year operator""y(unsigned long long y) noexcept;