@article{IM2_1970_4_6_a3,
     author = {A. M. Samoilenko},
     title = {Preservation of an invariant torus under perturbation},
     journal = {Izvestiya. Mathematics},
     pages = {1225--1249},
     year = {1970},
     volume = {4},
     number = {6},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_1970_4_6_a3/}
}