  This manuscript is an extended version of the author's habilitation thesis
defended on May 21, 2021 at M.V. Lomonosov Moscow State University. It is
devoted to the study of (co)stability of radicals, existence of (co)invariant
Levi and Wedderburn decompositions, structure of the corresponding simple
algebras and codimension growth of polynomial identities in (co)module algebras
over bi- and Hopf algebras and their generalizations. The main difference
between this manuscript and the "official" thesis are additional chapters
dealing with equivalences of gradings and Hopf algebra (co)actions, V-universal
(co)acting bi- and Hopf algebras and related categorical questions. (In
Russian.)
