@article{IM2_1986_26_2_a5,
     author = {E. A. Sevast'yanov},
     title = {On~an~estimate for the smallness of sets of points of nondifferentiability of functions as related to the degree of approximation by rational functions},
     journal = {Izvestiya. Mathematics },
     pages = {347--369},
     publisher = {mathdoc},
     volume = {26},
     number = {2},
     year = {1986},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_1986_26_2_a5/}
}