{∅, {∅}, {∅, {∅}}} : Rage Against the Meat Grinder

Just for the record (please skip this read if you have no interest in C++ or computer programming in general):  C++ Programming Language creator calls proposals 'insanity' ...

I don’t worry about other languages or new languages. I like programming languages. If a new language offers something useful that other languages don’t, it has a role and we can all learn from it. And then, of course, each language has its own problems. Many of C++’s problems relate to its very wide range of application areas, its very large and diverse user population, and overenthusiasm. Most language communities would love to have such problems.

For what it's worth ...

I'm just a Weirdo Rejectionist who is still interested in using [modern] C++ for my tinkerings with mathematics.   I'm not trying to be popular, in case you couldn't tell already.