@article{TRSPY_1971_112_a20,
     author = {S. M. Nikol'skii},
     title = {The preservation of class under a differentiable mapping},
     journal = {Informatics and Automation},
     pages = {327--336},
     publisher = {mathdoc},
     volume = {112},
     year = {1971},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TRSPY_1971_112_a20/}
}