1. Kühn J. H. andZerwas P. M., inZ Physics at LEP 1, edited byG. Altarelli, R. Kleiss andC. Verzegnassi, Vol.1 (CERN 89-08) 1989, p. 271.
2. Bardin D. et al., CERN-TH 6443/92 (May 1992);
3. Phys. Lett. B,255 (1991) 290;Nucl. Phys. B,351 (1991) 1;Z. Phys. C,44 (1989) 493.
4. L3Collaboration (B. Adeva et al.),Phys. Lett. B,241 (1990) 416.
5. ALEPHCollaboration (D. Decamp et al.),Phys. Lett. B,244 (1990) 551.