@article{DE_1967_3_5_a1,
     author = {V. A. Pliss},
     title = {Recurrent motions of periodic systems of two differential equations},
     journal = {Differencialʹnye uravneni\^a},
     pages = {722--732},
     publisher = {mathdoc},
     volume = {3},
     number = {5},
     year = {1967},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1967_3_5_a1/}
}