Recently, a lot of attention has been devoted to the influence of collinear gluon exchange in deep inelastic scattering and related processes. The most striking observable effect of the gluon exchange are transverse single spin asymmetries. In factorization formulae this effect is encoded in the gauge link appearing in the operator definition of parton distributions and fragmentation functions. The presence of the gauge link, however, makes the universality of such correlation functions a nontrivial issue. The main steps of these recent developments are summarized with a particular emphasis on the question of universality of T-odd fragmentation. A one-loop calculation suggests that T-odd fragmentation functions, in contrast to the corresponding parton distributions, are universal.

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