@article{DAN_1979_246_6_a4,
     author = {S. M. Ponomarev},
     title = {On the theory of boundary value problems for equations of mixed type in three-dimensional domains},
     journal = {Doklady Akademii Nauk},
     pages = {1303--1306},
     publisher = {mathdoc},
     volume = {246},
     number = {6},
     year = {1979},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1979_246_6_a4/}
}