@article{DAN_1989_304_2_a8,
     author = {B. T. Polyak and A. B. Tsybakov},
     title = {Optimal projection estimates for a regression function of unknown},
     journal = {Doklady Akademii Nauk},
     pages = {297--301},
     publisher = {mathdoc},
     volume = {304},
     number = {2},
     year = {1989},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1989_304_2_a8/}
}