@article{DE_1987_23_3_a16,
     author = {A. Z. Ishmukhametov},
     title = {On the smoothness of solutions of the {Cauchy} problem for a second-order hyperbolic operator-differential equation},
     journal = {Differencialʹnye uravneni\^a},
     pages = {493--499},
     publisher = {mathdoc},
     volume = {23},
     number = {3},
     year = {1987},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1987_23_3_a16/}
}