For a given T>0,we prove,under the global ARS-condition and using the Nehari manifold method,the existence of a T-periodic solution having the W-symmetry introduced in[21],for the hamiltonian system z+V'(z)=0,z∈R^N,N∈N^*.Moreover,such a solution is shown to have T as a minimal period without relaying to any index theory.A multiplicity result is also proved under the same condition.
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