@article {1989, title = {On the number of families of periodic solutions of a Hamiltonian system near equilibrium. II. (English. Italian summary)}, journal = {Boll. Un. Mat. Ital. B (7) 3 (1989), no. 3, 579-590}, number = {SISSA;13/88/FM}, year = {1989}, publisher = {SISSA Library}, url = {http://hdl.handle.net/1963/609}, author = {Gianfausto Dell{\textquoteright}Antonio and Biancamaria D{\textquoteright}Onofrio} }