Topics in Modern Mathematics: Petrovskii Seminar: Contemporary Soviet mathematics

An Exponential Estimate of the Time of Stability of Nearly Integrable Hamiltonian Systems. II.- Local Orbitals of Normal Forms of Vector Fields on a Plane.- Neighborhoods of Zero Type in Embedded Complex Tori.- Solution of a Hyperbolic Cauchy Problem with Characteristic Points in the Initial Surface.- A Variant of a Phragmén-Lindelöf Theorem for Elliptic Equations with Coefficients that are Periodic Functions of all Variables Except One.- Qualitative Theory of Open Homogeneous Cosmological Models with Motion of Matter.- Versal Deformations of Equivariant Vector Fields for the Cases of Symmetries of Order 2 and 3.- On Schreier Varieties of n-Groups and n-Semigroups.- Two-Variable Identities in the Lie Algebra sl(2, k).- Some Factor Groups of a Free Product.- Quasilinear Parabolic Equations and Systems with Two Independent Variables.