When I studied at Novosibirsk State University (Russian) I was lucky to have such brilliant teachers in mathematics as M.A. Lavrentyev, S.L. Sobolev, A.I. Mal’tsev, Yu.G. Reshetnyak and others. But it were L.V. Ovsyannikov’s lectures in Ordinary differential equations, Partial differential equations, Gas dynamics and Group properties of differential equations that were of the most benefit f…