@article{DE_1979_15_9_a9,
     author = {V. E. Chernyshev},
     title = {Existence of closed trajectories in the neighborhood of an invariant torus},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1620--1631},
     publisher = {mathdoc},
     volume = {15},
     number = {9},
     year = {1979},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1979_15_9_a9/}
}