above the pion production threshold, but not in the lower energy quasi-elastic region. Part of our effort is devoted to providing such fits. The inelastic data is represented in terms of structure functions or response functions. The overall polarizability effect is sensitive to the structure of the response functions at low energy and low virtual photon masses, which is where the data is sparse. A consequence of this, phrased in terms of fitting procedures, is that small changes in some parameters have big effects on the near threshold behavior but small effect on the quality of the fits to the available data. This leads to a larger than desired uncertainty in the results for the two-photon corrections, when using this method.

Future low momentum transfer deuteron breakup data, possibly obtained as background data to elastic scattering experiments [@modkg], can bring about a decisive reduction in the uncertainty limits of the polarizability calculation. We discuss this below with some examples.

Our presentation starts with the description of the general dispersive formalism for obtaining energy shifts from elastic and inelastic scattering data and subtraction terms in Section II. Evaluation of the elastic and inelastic dispersion integrals is discussed in Section III where 