@article{SM_1981_39_4_a3,
     author = {K. Yu. Osipenko},
     title = {Best approximation methods and the order of informativeness of systems},
     journal = {Sbornik. Mathematics},
     pages = {479--500},
     publisher = {mathdoc},
     volume = {39},
     number = {4},
     year = {1981},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1981_39_4_a3/}
}