@article{DE_1965_1_7_a0,
     author = {Ya. V. Bykov},
     title = {On singular periodic solutions of systems of ordinary differential equations},
     journal = {Differencialʹnye uravneni\^a},
     pages = {851--867},
     publisher = {mathdoc},
     volume = {1},
     number = {7},
     year = {1965},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1965_1_7_a0/}
}