@article{DAN_1990_313_3_a7,
     author = {V. V. Kovtunets},
     title = {Differentiability of an operator of best uniform approximation of},
     journal = {Doklady Akademii Nauk},
     pages = {548--551},
     publisher = {mathdoc},
     volume = {313},
     number = {3},
     year = {1990},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1990_313_3_a7/}
}