@article{GDZPPN002090384, title = {Normal Modes for Nonlinear Hamiltonian Systems.}, journal = {Inventiones mathematicae}, volume = {20}, year = {1973}, pages = {47-58}, zbl = {0264.70020}, url = {http://dml.mathdoc.fr/item/GDZPPN002090384} }
Weinstein, Alan. Normal Modes for Nonlinear Hamiltonian Systems.. Inventiones mathematicae, Tome 20 (1973) pp. 47-58. http://gdmltest.u-ga.fr/item/GDZPPN002090384/