@article{DE_1985_21_4_a7,
     author = {G. S. Osipenko},
     title = {Perturbation of invariant manifolds. {I}},
     journal = {Differencialʹnye uravneni\^a},
     pages = {615--623},
     publisher = {mathdoc},
     volume = {21},
     number = {4},
     year = {1985},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1985_21_4_a7/}
}