@article{DAN_1981_259_3_a9,
     author = {Kh. G. Umarov},
     title = {Riemann's method for some hyperbolic equations with constant operator coefficients},
     journal = {Doklady Akademii Nauk},
     pages = {549--553},
     publisher = {mathdoc},
     volume = {259},
     number = {3},
     year = {1981},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1981_259_3_a9/}
}