Determination of two-photon exchange amplitudes from elastic electron-proton scattering data J. Guttmann, N. Kivel, M. Meziane and M. Vanderhaeghen Eur. Phys. J. A, 47 6 (2011) 77 Published online: 16 June 2011 DOI: 10.1140/epja/i2011-11077-4