@article{DAN_1994_335_3_a9,
     author = {B. T. Polyak and Ya. Z. Tsypkin},
     title = {Robust aperiodicity},
     journal = {Doklady Akademii Nauk},
     pages = {304--307},
     year = {1994},
     volume = {335},
     number = {3},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1994_335_3_a9/}
}