@article{02173970,
title = {Periodic solutions of a resonant higher order equation.},
journal = {Portugaliae Mathematica. Nova S\'erie},
volume = {61},
year = {2005},
pages = {13-24},
zbl = {1084.34043},
language = {en},
url = {http://dml.mathdoc.fr/item/02173970}
}
Amster, P.; de Nápoli, P.; Mariani, M.C. Periodic solutions of a resonant higher order equation.. Portugaliae Mathematica. Nova Série, Tome 61 (2005) pp. 13-24. http://gdmltest.u-ga.fr/item/02173970/