@article{DE_1973_9_5_a4,
     author = {A. S. Gurtovnik and Yu. I. Neimark},
     title = {Investigation of the neighborhood of a family of invariant toroidal manifolds},
     journal = {Differencialʹnye uravneni\^a},
     pages = {821--831},
     publisher = {mathdoc},
     volume = {9},
     number = {5},
     year = {1973},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1973_9_5_a4/}
}