@article{DE_1990_26_1_a8,
     author = {N. Yu. Kapustin},
     title = {Solvability in the class $L_2$ of a problem with a boundary condition on a characteristic for a hyperbolic equation with order degeneration},
     journal = {Differencialʹnye uravneni\^a},
     pages = {66--75},
     publisher = {mathdoc},
     volume = {26},
     number = {1},
     year = {1990},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1990_26_1_a8/}
}