1. P.H. Chankowski, J. Ellis, S. Pokorski, hep-ph/9712234.
2. J. Ellis, K. Enqvist, D.V. Nanopoulos, F. Zwirner, Nucl. Phys. B 276 (1986) 14; R. Barbieri, G.F. Giudice, Nucl. Phys. B 306 (1988) 63.
3. D. Ward, plenary talk at the Europhysics Conference on High-Energy Physics, Jerusalem, August 1997.
4. M.S. Alam et al., Phys. Rev. Lett. 74 (1995) 2885.
5. P. Janot, plenary talk at the Europhysics Conference on High-Energy Physics, Jerusalem, August 1997; open session of the LEP experiments committee, November 1997.