@article{DAN_1981_261_6_a3,
     author = {V. V. Lychagin},
     title = {Geometric singularities of solutions of nonlinear differential equations},
     journal = {Doklady Akademii Nauk},
     pages = {1299--1303},
     publisher = {mathdoc},
     volume = {261},
     number = {6},
     year = {1981},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1981_261_6_a3/}
}