1. For a recent and updated schematical review of this subject see, e.g.: R. Gatto, C. Casalbuoni, D. Dominici, F. Feruglio, in: Z Physics at LEP1, CERN-89-08; G. Altarelli, R. Kleiss, C. Verzegnassi (eds.); F. Boudjema, F.M. Renard, in: Polarization at LEP, CERN-88-06, G. Alexander et al. (eds.), and references therein
2. U. Amaldi et al.: Phys. Rev. D36 (1987) 1385
3. G. Costa et al.: Nucl. Phys. B297 (1988) 244
4. G. Altarelli, R. Casalbuoni, F. Feruglio, R. Gatto: CERN-TH-5752/90, UGVA-DPT 1990/05-670
5. D. London, J.L. Rosner: Phys. Rev. D34 (1986) 1530