std::chrono::year::operator+, std::chrono::year::operator-

constexpr std::chrono::year operator+() noexcept;	(1)	(since C++20)
constexpr std::chrono::year operator-() noexcept;	(2)	(since C++20)

Applies the unary operators to the year value.

1) Returns a copy of *this.

2) Returns a year whose year value is the negation of that of *this.

1) *this

2) std::chrono::year(-int(*this))

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