Two-photon exchange in elastic electron-proton scattering P.G. Blunden, W. Melnitchouk and J.A. Tjon Eur. Phys. J. A, 24 Supplement 1 (2005) s1.59-s1.63 Published online: 08 February 2005 DOI: 10.1140/epjad/s2005-05-010-2