@article {1987, title = {Solutions with minimal period for Hamiltonian systems in a potential well.}, journal = {Ann. Inst. H. Poincare Anal. Non Lineaire 4 (1987), no. 3, 275-296}, number = {SISSA;79/85/M}, year = {1987}, publisher = {SISSA Library}, url = {http://hdl.handle.net/1963/466}, author = {Antonio Ambrosetti and Vittorio Coti Zelati} }