[mehrdadn]

C++20 doesn't quite rectify this unfortunately! The data structures still use std::less even in C++20, meaning the 2-way comparisons would happen twice. Except now each 2-way comparison is potentially implemented on top of 3-way comparisons. Perhaps I or someone else should get in touch with the committee to try to change that, otherwise things are going to be slower rather than faster if we still use 2-way comparisons but now they have to do 3-way comparisons underneath!