@article{SM_2007_198_7_a4,
     author = {I. A. Rudakov},
     title = {Periodic solutions of a~quasilinear wave equation with},
     journal = {Sbornik. Mathematics},
     pages = {993--1009},
     year = {2007},
     volume = {198},
     number = {7},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_2007_198_7_a4/}
}