@article{DAN_1989_304_4_a8,
     author = {V. G. Romanov},
     title = {Solvability of inverse problems for hyperbolic equations in a},
     journal = {Doklady Akademii Nauk},
     pages = {807--811},
     year = {1989},
     volume = {304},
     number = {4},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1989_304_4_a8/}
}