@article{DAN_1977_237_2_a0,
     author = {V. M. Isakov},
     title = {On the inverse problem of the potential for hyperbolic equations},
     journal = {Doklady Akademii Nauk},
     pages = {257--259},
     publisher = {mathdoc},
     volume = {237},
     number = {2},
     year = {1977},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1977_237_2_a0/}
}