@article{SM_1977_32_2_a4,
     author = {V. A. Popov and P. P. Petrushev},
     title = {The exact order of the best approximation to convex functions by~rational functions},
     journal = {Sbornik. Mathematics},
     pages = {245--251},
     publisher = {mathdoc},
     volume = {32},
     number = {2},
     year = {1977},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1977_32_2_a4/}
}