Report of the working group on radiative corrections at HERA

Abstract
In inclusive deep-inelastic lepton-nucleon scattering, the radiative 'tails' originating from processes at Q2 values from the interval Q2meas >= Q2 > 0 contribute to measurements at Q2 = Q2meas and a knowledge of the structure functions in this Q2 interval is necessary. We review and compare existing parametrizations of structure functions and their extrapolations into the as-yet unexplored very low-Q2 regions and discuss the resulting uncertainties for leptonic radiative corrections. The unfolding procedures to determine structure functions from observed cross sections by the experiments NMC, ZEUS and H1 are compared with each other.