B. Gr bert and T. Kappeler
Perturbations of the defocusing NLS equation
(76K, Latex2e)

ABSTRACT.   We prove that many finite dimensional tori, invariant 
under the flow of the defocusing nonlinear Schr\"odinger equation, 
persist under small Hamiltonian perturbations.These invariant 
tori are not necessarily close to the zero solution.