@article{DAN_1990_313_2_a1,
     author = {V. F. Lazutkin},
     title = {The width of the instability zone around separatrices of a},
     journal = {Doklady Akademii Nauk},
     pages = {268--272},
     publisher = {mathdoc},
     volume = {313},
     number = {2},
     year = {1990},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1990_313_2_a1/}
}