@article{FAA_1988_22_4_a15,
     author = {B. V. Lidskii and E. I. Shulman},
     title = {Periodic solutions of the equation $u_{tt}-u_{xx}+u^3=0$},
     journal = {Funkcionalʹnyj analiz i ego prilo\v{z}eni\^a},
     pages = {88--89},
     publisher = {mathdoc},
     volume = {22},
     number = {4},
     year = {1988},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/FAA_1988_22_4_a15/}
}