Duality is considered for the perturbation theory by deriving, given a series
solution in a small parameter, its dual series with the development parameter
being the inverse of the other. A dual symmetry in perturbation theory is
identified. It is then shown that the dual to the Dyson series in quantum
mechanics is given by a recent devised series having the adiabatic
approximation as leading order. A simple application of this result is given by
rederiving a theorem for strongly perturbed quantum systems.Comment: 9 pages, revtex. Improved english and presentation. Final version
accepted for publication by Physical Review