@article{DE_1976_12_7_a4,
     author = {D. V. Izyumova and J. D. Mirzov},
     title = {The oscillation and the disconjugacy of the solutions of nonlinear differential systems},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1187--1193},
     publisher = {mathdoc},
     volume = {12},
     number = {7},
     year = {1976},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1976_12_7_a4/}
}