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