@article{DE_1994_30_7_a6,
     author = {V. V. Filippov},
     title = {Sequences of changes of variables and the {Li\'enard} equation},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1148--1155},
     publisher = {mathdoc},
     volume = {30},
     number = {7},
     year = {1994},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1994_30_7_a6/}
}