19 Diagnostics library [diagnostics]

19.5 System error support [syserr]

19.5.3 Class error_category [syserr.errcat]

19.5.3.3 Non-virtual members [syserr.errcat.nonvirtuals]

bool operator==(const error_category& rhs) const noexcept;
Returns: this == &rhs.
strong_ordering operator<=>(const error_category& rhs) const noexcept;
Returns: compare_three_way()(this, &rhs).
[Note 1: 
compare_three_way ([comparisons.three.way]) provides a total ordering for pointers.
— end note]