@article{DAN_1969_184_6_a5,
     author = {M. E. Lerner},
     title = {The extremal property of the solutions of a certain class of hyperbolic equations},
     journal = {Doklady Akademii Nauk},
     pages = {1281--1283},
     publisher = {mathdoc},
     volume = {184},
     number = {6},
     year = {1969},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1969_184_6_a5/}
}