@article{DE_1999_35_12_a5,
     author = {I. N. Sergeev},
     title = {The rotation method and singular numbers of three-dimensional systems},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1630--1639},
     publisher = {mathdoc},
     volume = {35},
     number = {12},
     year = {1999},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1999_35_12_a5/}
}