Hi, you’ve done an amazing job at distilling a language as complex as C++ down to some core elements. As you already mentioned, containers and algorithms are potential concepts that could still be added.
Personally, I’d still include std::string_view, however, I don’t know to what degree this makes sense given that the string concept is earlier than the reference concept, both necessary to understand the use case for string_view. Maybe it could be a new concept that requires both?