@article{GDZPPN002230593, title = {Subharmonics near an equilibrium point for Hamiltonian systems.}, journal = {Manuscripta mathematica}, volume = {67}, year = {1990}, pages = {359-396}, zbl = {0688.34027}, url = {http://dml.mathdoc.fr/item/GDZPPN002230593} }
Felmer, Patricio L. Subharmonics near an equilibrium point for Hamiltonian systems.. Manuscripta mathematica, Tome 67 (1990) pp. 359-396. http://gdmltest.u-ga.fr/item/GDZPPN002230593/