@article{DAN_1981_256_6_a5,
     author = {G. M. Kagan},
     title = {On a class of singular problems satisfying {Huygens} principle},
     journal = {Doklady Akademii Nauk},
     pages = {1307--1311},
     publisher = {mathdoc},
     volume = {256},
     number = {6},
     year = {1981},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1981_256_6_a5/}
}