Natural invariants and classification of quasilinear second-order differential operators

This talk is based on joint research with Valery Yumaguzhin.
In the first part, we outline the method of finding rational natural differential invariants of a class of quasilinear second-order differential operators, and then we show how these invariants could be used to get local as well as global classification of such type operators with respect to the diffeomorphism group.