@article{SM_1991_70_1_a1,
     author = {P. L. Ul'yanov},
     title = {On~classes of infinitely differentiable functions},
     journal = {Sbornik. Mathematics},
     pages = {11--30},
     publisher = {mathdoc},
     volume = {70},
     number = {1},
     year = {1991},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1991_70_1_a1/}
}