1. For a recent review see, for example, A.J. Buras, R. Fleischer, hep-ph/9704376, to appear in Heavy Flavours II, A.J. Buras, M. Lindner (Eds.), World Scientific, 1997.
2. A.E. Snyder, H.R. Quinn, Phys. Rev. D 48 (1993) 2139.
3. The BaBar Physics Book, Chapter 6, SLAC-R-504, in preparation.
4. L. Wolfenstein, Phys. Rev. Lett. 51 (1983) 1945.
5. B. Kayser, hep-ph/9709382, to appear in the Proceedings of the Moriond Workshop on Electroweak Interactions and Unified Theories, Les Arcs, France, March 1997.