@article{DE_1980_16_2_a23,
     author = {V. E. Chernyshev},
     title = {Closed trajectories in the neighborhood of an invariant torus},
     journal = {Differencialʹnye uravneni\^a},
     pages = {374--376},
     publisher = {mathdoc},
     volume = {16},
     number = {2},
     year = {1980},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1980_16_2_a23/}
}