I am a middle-aged man, and I have forgotten a lot of math. In order to give guidance to children, I am studying again now. I bought a set of math textbooks online and read them when I have time, mainly to familiarize myself with basic concepts, axioms and theorems. Some of them are derived by myself, and some of the mid-term exam questions have been done, so I won't look them up again.

Sometimes I answer here, but it's always not as fast as young people. Ha ha.