@article{DE_1971_7_12_a11,
     author = {P. V. Sokolov},
     title = {A geometric picture of the integral surfaces near a singular integral element of a first order partial differential equation},
     journal = {Differencialʹnye uravneni\^a},
     pages = {2225--2233},
     publisher = {mathdoc},
     volume = {7},
     number = {12},
     year = {1971},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1971_7_12_a11/}
}