std::chrono::operator+, std::chrono::operator- (std::chrono::year_month_weekday)
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                    < cpp | chrono | year month weekday
                    
                                                            
                    | constexpr std::chrono::year_month_weekday  operator+(const std::chrono::year_month_weekday& ymwd, const std::chrono::months& dm) noexcept; | (1) | (since C++20) | 
| constexpr std::chrono::year_month_weekday  operator+(const std::chrono::months& dm, const std::chrono::year_month_weekday& ymwd) noexcept; | (2) | (since C++20) | 
| constexpr std::chrono::year_month_weekday  operator+(const std::chrono::year_month_weekday& ymwd, const std::chrono::years& dy) noexcept; | (3) | (since C++20) | 
| constexpr std::chrono::year_month_weekday  operator+(const std::chrono::years& dy, const std::chrono::year_month_weekday& ymwd) noexcept; | (4) | (since C++20) | 
| constexpr std::chrono::year_month_weekday operator-(const std::chrono::year_month_weekday& ymwd, const std::chrono::months& dm) noexcept; | (5) | (since C++20) | 
| constexpr std::chrono::year_month_weekday  operator-(const std::chrono::year_month_weekday& ymwd, const std::chrono::years& dy) noexcept; | (6) | (since C++20) | 
1-2) Adds dm.count() months to the date represented by 
ymwd. The result has the same year() and month() as std::chrono::year_month(ymwd.year(), ymwd.month()) + dm and the same weekday() and index() as ymwd.3-4) Adds dy.count() years to the date represented by 
ymwd. The result is equivalent to std::chrono::year_month_weekday(ymwd.year() + dy, ymwd.month(), ymwd.weekday_indexed()).5) Subtracts dm.count() months from the date represented by 
ymwd. Equivalent to ymwd + -dm.6) Subtracts dy.count() years from the date represented by 
ymwd. Equivalent to ymwd + -dy.Notes
Even if ymwd.ok() is true, the resulting year_month_weekday may not represent a valid date if ymwd.index() is 5.