@article{DE_1983_19_12_a9,
     author = {G. V. Zhidkov},
     title = {Differential properties of functions on the sphere},
     journal = {Differencialʹnye uravneni\^a},
     pages = {2090--2101},
     publisher = {mathdoc},
     volume = {19},
     number = {12},
     year = {1983},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1983_19_12_a9/}
}