1. A. Capella, U. Sukhatme, J. Tran Thanh Van: Z. Phys. C ?Particles and Fields3, 329 (1980); A. Capella, U. Sukhatme, C.-I Tan, J. Tran Thanh Van; Phys. Lett.81B, 68 (1979)
2. H. Minakata: Phys. Rev. D20, 1656 (1979); G. Cohen-Tannoudji et al.: Phys. Rev. D21, 2699 (1980); D19, 3397 (1979); B. Andersson, G. Gustafson, C. Peterson: Phys. Lett.69B, 221 (1977);71B, 337 (1977); S. Brodsky, J. Gunion: Phys. Rev. D17, 848 (1978)
3. R. Hwa: In Proc. 12th Int. Symposium on Multiparticle Dynamics, Notre Dame, Indiana (1981); K. Das. R. Hwa: Phys. Lett.68B, 549 (1977); L. Van Hove, S. Pokorski: Nucl. Phys. B86, 243 (1975); W. Ochs: Nucl. Phys. B118, 397 (1977)
4. J. Gunion: In: Partons in soft-hadronic processes. Erice, Sicily (1981), ed. R. Van de Walle; F. Low: Phys. Rev. D12, 163 (1975); S. Nussinov: Phys. Rev. Lett.34, 1286 (1975)
5. R. Feynman: Photon-hadron interactions. New York: Benjamin 1972; G. Farrar, J. Rosner: Phys. Rev. D9, 2658 (1974); S. Brodsky, N. Weiss: Phys. Rev. D16, 2325 (1977); W. Ochs, T. Shimada: Z. Phys. C?Particles and Fields4, 141 (1980)