@article{DE_1990_26_3_a15,
     author = {S. E. Pastukhova},
     title = {On the loss of smoothness of the solution of a mixed problem with an oblique derivative for the wave operator},
     journal = {Differencialʹnye uravneni\^a},
     pages = {478--488},
     publisher = {mathdoc},
     volume = {26},
     number = {3},
     year = {1990},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1990_26_3_a15/}
}