@article{IM2_1977_11_1_a5,
     author = {E. P. Dolzhenko and V. I. Danchenko},
     title = {Dependence of the differentiability of functions of several variables on their rate of approximation by rational functions},
     journal = {Izvestiya. Mathematics },
     pages = {171--192},
     publisher = {mathdoc},
     volume = {11},
     number = {1},
     year = {1977},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_1977_11_1_a5/}
}