@article{10_21136_AM_1969_103218,
     author = {Vejvoda, Otto},
     title = {Periodic solutions of a weakly nonlinear wave equation in $E_3$ in a spherically symmetrical case},
     journal = {Applications of Mathematics},
     pages = {160--167},
     publisher = {mathdoc},
     volume = {14},
     number = {2},
     year = {1969},
     doi = {10.21136/AM.1969.103218},
     mrnumber = {0239247},
     zbl = {0175.39504},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.21136/AM.1969.103218/}
}