@article{MM2_1989__64_2_155414,
     author = {Maria Letizia Bertotti},
     title = {Multiplicity of {Subharmonic} solutions of {Forces} {Hamiltonian} systems near an equilibrium.},
     journal = {Manuscripta mathematica},
     pages = {389--402},
     publisher = {mathdoc},
     volume = {64},
     number = {2},
     year = {1989},
     zbl = {0672.70020},
     url = {http://geodesic.mathdoc.fr/item/MM2_1989__64_2_155414/}
}