@article{MM2_1980__32_154723,
     author = {Herbert Amann and Eduard Zehnder},
     title = {Periodic {Solutions} of {Asymptotically} {Linear} {Hamiltonian} {Systems.}},
     journal = {Manuscripta mathematica},
     pages = {149--190},
     publisher = {mathdoc},
     volume = {32},
     year = {1980},
     zbl = {0443.70019},
     url = {http://geodesic.mathdoc.fr/item/MM2_1980__32_154723/}
}