Two-photon exchange and elastic scattering of electrons/positrons on the   proton. (Proposal for an experiment at VEPP-3)
  It has been suggested that two-photon exchange corrections could explain the discrepancy between Rosenbluth extractions of the proton form factors and recent polarization transfer measurements. We propose a precise comparison of electron-proton and positron-proton scattering at Q^2=1.6 GeV^2 to determine if two-photon exchange at moderate Q^2 values is in fact able to explain the discrepancy. 
J. Arrington, V.F. Dmitriev, R.J. Holt, D.M. Nikolenko, I.A. Rachek,   Yu.V.Shestakov, V.N. Stibunov, D.K. Toporkov, H.de Vries