@article{DE_1968_4_1_a4,
     author = {A. M. Nakhushev},
     title = {A three-dimensional analog of {Gellerstedt's} problem},
     journal = {Differencialʹnye uravneni\^a},
     pages = {52--62},
     year = {1968},
     volume = {4},
     number = {1},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1968_4_1_a4/}
}