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@article{DE_1987_23_2_a3, author = {A. I. Bulgakov}, title = {On the oscillation of solutions of systems of second-order differential equations}, journal = {Differencialʹnye uravneni\^a}, pages = {204--217}, publisher = {mathdoc}, volume = {23}, number = {2}, year = {1987}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/DE_1987_23_2_a3/} }
A. I. Bulgakov. On the oscillation of solutions of systems of second-order differential equations. Differencialʹnye uravneniâ, Tome 23 (1987) no. 2, pp. 204-217. http://geodesic.mathdoc.fr/item/DE_1987_23_2_a3/