In C++23, what happens when a class defines auto operator<=>(const T&) const = default; a…

In C++23, what happens when a class defines auto operator<=>(const T&) const = default; and declares no operator==?

1. A matching defaulted operator== is declared implicitly.
2. Equality is unavailable until operator== is written by hand.
3. operator== compares object addresses.
4. The declaration is valid only for classes with one data member.