I don't know. Even Komolgorov's "Mathematics: Its Content, Methods and Meaning" is pretty easy to read. My theory is that instead of teaching the abstract defi

I don't know. Even Komolgorov's "Mathematics: Its Content, Methods and Meaning" is pretty easy to read. My theory is that instead of teaching the abstract definition and proofs for group like general college math professors, V.I. Arnold might start lectures from some games/problems in daily life that we can apply group theory on to kids. (Of course those kids maybe gifted in math already) then from the special concrete case as basis, he then showed students the abstract stuffs behind it.