@article{1183531828,
author = {Berger, Melvyn S.},
title = {On periodic solutions of nonlinear hyperbolic equations and the calculus of variations},
journal = {Bull. Amer. Math. Soc.},
volume = {76},
number = {4},
year = {1970},
pages = { 633-637},
language = {en},
url = {http://dml.mathdoc.fr/item/1183531828}
}
Berger, Melvyn S. On periodic solutions of nonlinear hyperbolic equations and the calculus of variations. Bull. Amer. Math. Soc., Tome 76 (1970) no. 4, pp. 633-637. http://gdmltest.u-ga.fr/item/1183531828/