@article{DAN_1992_323_2_a12,
     author = {M. M. Khapaev},
     title = {Singular differential equations in problems on the investigation},
     journal = {Doklady Akademii Nauk},
     pages = {250--252},
     publisher = {mathdoc},
     volume = {323},
     number = {2},
     year = {1992},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1992_323_2_a12/}
}