@article{DAN_1992_326_6_a4,
     author = {I. L. Sofronov},
     title = {Conditions for complete transparency on a sphere for a},
     journal = {Doklady Akademii Nauk},
     pages = {953--957},
     publisher = {mathdoc},
     volume = {326},
     number = {6},
     year = {1992},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1992_326_6_a4/}
}