@article {1987, title = {Symmetry breaking in Hamiltonian systems}, journal = {J. Differential Equations 67 (1987), no. 2, 165-184}, number = {SISSA;22/85/M}, year = {1987}, publisher = {SISSA Library}, url = {http://hdl.handle.net/1963/409}, author = {Antonio Ambrosetti and Vittorio Coti Zelati and Ivar Ekeland} }