@article{RM_1969_24_2_a12,
     author = {O. A. Oleinik},
     title = {On second order hyperbolic equations degenerating in the interior of a~region and on its boundary},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     publisher = {mathdoc},
     volume = {24},
     number = {2},
     year = {1969},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/RM_1969_24_2_a12/}
}