It is a well-known fact that, among the electroweak corrections, QEDradiation gives the largest contribution and the needed precision requires are-summation of the large logarithms which show up in perturbation theory. Fortwo fermion annihilation processes initial state radiation is a definable,gauge-invariant, concept and one has general tools to deal with it; thestructure function approach and also the parton-shower method. However, whenone tries to apply the algorithm to four-fermion processes that includenon-annihilation channels a problem is faced: is it still possible to includeQED corrections by making use of the standard tools? A systematization isattempted of several, recently proposed, algorithms. In particular, it is shownthat starting from the exponentiation of soft photons one can still derive adescription of QED radiation in terms of structure functions, i.e. the kernelfor the hard scattering is convoluted with generalized structure functionswhere each of them is no longer function of one scale.
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