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  • KAM Theory without action--angle variables 

    González, Alejandra; Jorba, Angel; Llave Canosa, Rafael de la; Villanueva Castelltort, Jordi (2003)
    Open Access
    Given a torus approximately invariant under a symplectic map, we find sufficient conditions for the existence of a true invariant torus close to the given one. We do not assume either that we are working on action-angle ...