@article {2005,
	title = {Periodic solutions of nonlinear wave equations with non-monotone forcing terms},
	journal = {Atti Accad. Naz. Lincei Cl. Sci. Fis. Mat. Natur. Rend. Lincei (9) Mat. Appl. 16 (2005), no. 2, 117-124},
	year = {2005},
	publisher = {Accademia Nazionale dei Lincei},
	url = {http://hdl.handle.net/1963/4581},
	author = {Massimiliano Berti and Luca Biasco}
}
