Here are the "Arnold's problems" — which every Russian kid even slightly mathematically inclined have seen and worked on many times: https://www.imaginary.org/s

Here are the "Arnold's problems" — which every Russian kid even slightly mathematically inclined have seen and worked on many times: https://www.imaginary.org/sites/default/files/taskbook_arnold_en_0.pdf https://www.imaginary.org/sites/default/files/taskbook_arnol.... It is really good, in my opinion.