@article{DAN_1957_113_1_a7,
     author = {V. M. Tsodyks},
     title = {On sets of points where the derivative is $+\infty$ or $-\infty$ correspondingly},
     journal = {Doklady Akademii Nauk},
     pages = {36--38},
     publisher = {mathdoc},
     volume = {113},
     number = {1},
     year = {1957},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1957_113_1_a7/}
}