@article{DAN_1996_351_1_a6,
     author = {A. A. Melikyan},
     title = {Singular characteristics of first-order partial differential},
     journal = {Doklady Akademii Nauk},
     pages = {24--28},
     year = {1996},
     volume = {351},
     number = {1},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1996_351_1_a6/}
}