@article{DAN_1972_205_1_a0,
     author = {A. V. Bitsadze and A. M. Nakhushev},
     title = {Correct formulations of problems for equations of mixed type in multidimensional domains},
     journal = {Doklady Akademii Nauk},
     pages = {9--12},
     publisher = {mathdoc},
     volume = {205},
     number = {1},
     year = {1972},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1972_205_1_a0/}
}