@article{DAN_1968_182_6_a3,
     author = {V. N. Gol'dberg},
     title = {The occurrence of discontinuities when extending solutions of nonlinear mixed problems for hyperbolic equations on the plane},
     journal = {Doklady Akademii Nauk},
     pages = {1257--1260},
     publisher = {mathdoc},
     volume = {182},
     number = {6},
     year = {1968},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1968_182_6_a3/}
}