Radiative corrections due to the production of virtual as well as real soft
and hard pairs in small-angle Bhabha scattering are calculated analytically.
Both the collinear and the semi-collinear kinematical regions of hard pair
production are considered. The calculation, within the leading and
next-to-leading logarithmic approximation, provides an accuracy of O(0.1%).
Numerical results show that the effects of pair production have to be taken
into account for a luminosity determination accurate to O(0.1%) at LEP.Comment: Latex. 20 page
