@article{DE_1993_29_2_a6,
     author = {D. S. Ushkho},
     title = {On the number of singular points of the second group of a cubic system},
     journal = {Differencialʹnye uravneni\^a},
     pages = {240--245},
     publisher = {mathdoc},
     volume = {29},
     number = {2},
     year = {1993},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1993_29_2_a6/}
}