1. Y. Fukuda et al., hep-ex/9805006, hep-ex/9805021 and hep-ex/9807003.
2. The data on solar neutrinos from Homestake, Gallex, Sage, Kamiokande and Superkamiokande are summarized and the list of references given in J.N. Bahcall, P.I. Krastev, A. Yu Smirnov, hep-ph/9807216.
3. G. Altarelli, F. Feruglio, hep-ph/9905536 and references therein.
4. C. Athanassopoulos et al., Phys. Rev. Lett. 77 (1996) 3082; nucl-ex/9706006, nucl-ex/9709006.
5. B. Armbruster et al., Phys. Rev. C57 (1998) 3414; G. Drexlin, talk at Wein'98.