@article{DAN_1975_223_6_a0,
     author = {A. V. Bitsadze},
     title = {On the question of formulating the characteristic problem for second order hyperbolic systems},
     journal = {Doklady Akademii Nauk},
     pages = {1289--1292},
     publisher = {mathdoc},
     volume = {223},
     number = {6},
     year = {1975},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1975_223_6_a0/}
}