Belova M.M., “Ogranichennye resheniya sistem nelineinykh obyknovennykh differentsialnykh uravnenii vtorogo poryadka”, Doklady AN SSSR, 9 (1968), 603–606 , translation from Dokl. Akad. Nauk SSSR 180, 266-268 (1968).Bounded solutions of systems of second order ordinary differential equations. (Russian)
M. M. Belova, “On bounded solutions of non-linear second-order differential equations”, Mat. Sb. (N.S.), 56(98):4 (1962), 469–503
Belova M.M., “Ogranichennye resheniya sistem nelineinykh obyknovennykh differentsialnykh uravnenii vtorogo poryadka”, Doklady AN SSSR, 9 (1968), 603–606 , translation from Dokl. Akad. Nauk SSSR 180, 266-268 (1968).Bounded solutions of systems of second order ordinary differential equations. (Russian)
5.
M. M. Belova, “Bounded solutions of systems of second order ordinary differential equations”, Dokl. Akad. Nauk SSSR, 180:2 (1968), 266–268