@article{DE_2006_42_8_a0,
     author = {Yu. N. Bibikov and M. V. Pirogov},
     title = {Invariant tori of the {Duffing} equation},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1011--1016},
     publisher = {mathdoc},
     volume = {42},
     number = {8},
     year = {2006},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_2006_42_8_a0/}
}