1. D. Griffith, Introduction to Elementary Particles (Wiley, New York, 1987).
2. F. Halzen and A. D. Martin, Quarks and Leptons: An Introductory Course in Modern Particle Physics (Wiley, New York, 1990).
3. G. Wolf, First Results from HERA (DESY, 1992).
4. B. Foster, Int. J.Mod. Phys. A 13, 1543 (1998).
5. Y. L. Dokshitzer, Sov. Phys. JETP 46, 641 (1977)