1. H. Rollnik, these proceedings.
2. A. Schäfer, these proceedings.
3. J. Ashman et al., Phys. Lett. B206 (1988) 364, Nucl. Phys. B328 (1989) 1.
4. J.D. Bjorken, Phys. Rev. 148 (1966) 1467, D1 (1970) 1376.
5. see for instance M. Glück and E. Reya, Z. Phys. C39 (1988) 569.