@article{DAN_1972_204_6_a1,
     author = {A. V. Bitsadze and A. M. Nakhushev},
     title = {Theory of degenerate hyperbolic equations in multidimensional domains},
     journal = {Doklady Akademii Nauk},
     pages = {1289--1291},
     publisher = {mathdoc},
     volume = {204},
     number = {6},
     year = {1972},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1972_204_6_a1/}
}