1. For reviews see, for example: T. Sloan: Proceedings of the Int. EPS Conf. on High Energy Physics, Uppsala 1987, O. Botner (ed.) p. 857 (Uppsala Univ., 1987); R. Voss: Proceedings of the 1987 Int. Symp. on Lepton and Photon Interactions at High Energies, Hamburg, W. Bartel, R. Rückl (eds) p. 581 (Amsterdam: North-Holland, 1988); G. Altarelli: Ann. Rev. Nucl. Part. Sci. 39 (1989) 357
2. For a recent review see, for example, J. Feltesse: Proceedings of the XIV Int. Symposium on Lepton and Photon Interactions, Stanford, 1989, M. Riordan (ed.) p. 13. Singapore: World Scientific 1990
3. M. Glück, E. Hoffmann, E. Reya: Z. Phys. C—Particles and Fields 13 (1982) 119
4. P. Aurenche et al.: Phys. Rev. D39 (1989) 3275
5. A.P. Contogouris, S. Papadopoulos, D. Atwood: Direct photon production with complete QCD corrections and physical scales: Univ. McGill report, 1989