std::chrono::year::operator+, std::chrono::year::operator-
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                    | 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.Return value
1) *this
2) std::chrono::year(-int(*this))
Example
| This section is incomplete Reason: no example |