I think that subjects like math are better modeled as graphs of prerequisites rather than "levels". There are so many discrete areas that you can go into withou

I think that subjects like math are better modeled as graphs of prerequisites rather than "levels". There are so many discrete areas that you can go into without learning about others, it makes very little sense to categorize math the way we do before college. Even topics like "geometry" or "calculus" are too broad.