[Supplement to the article "On the indispensible conditions for the existance of periodical solutions of certain unlinear second order systems"].
D008433:Mathematics
Dopolnenie k stat'e "O neobkhodimykh usloviiakh sushchestvovaniia polozhitel'nykh periodicheskikh resheniĭ nekotorykh nelineĭnykh sistem vtorogo poriadka".