Minimal $P$-symmetric periodic solutions of nonlinear Hamiltonian   systems
  In this paper some existence results for the minimal P-symmetric periodic solutions are proved for first order autonomous Hamiltonian systems when the Hamiltonian function is superquadratic, asymptotically linear and subquadratic. These are done by using critical points theory, Galerkin approximation procedure, Maslov $P$-index theory and its iteration inequalities. 
Shanshan Tang
math.AP