@article{IM2_2006_70_1_a4,
     author = {I. A. Rudakov},
     title = {Periodic solutions of a non-linear wave equation with homogeneous boundary conditions},
     journal = {Izvestiya. Mathematics },
     pages = {109--120},
     publisher = {mathdoc},
     volume = {70},
     number = {1},
     year = {2006},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_2006_70_1_a4/}
}