1. Details can be found in the various review articles published in ‘Perturbative QCD’, edited by M Jacob, (North-Holland Pub. Co., 1982)
2. R P Feynman,Photon hadron interactions (Benjamin, 1972)
3. G Altarelli and G Parisi,Nucl. Phys. B126, 298 (1977)
4. G Curci, W Furmanski and R Petronzio,Nucl. Phys. B175, 27 (1980)
5. D J Gross and F Wilczek,Phys. Rev. D8, 3633 (1973)