1. M. N. Kinzle-Focacci, in Proc. of the VIII Blois Workshop, Protvino, Russia, 1999, Ed. by V. A. Petrov and A. V. Prokudin (World Sci., Singapore, 2000); V. A. Schegelsky, Talk Given in Open Session of HEP Division of PNPI “On the Eve of the XXI Century” (2000).
2. E. Klempt, hep-ex/0101031.
3. KLOE Collab. (A. Aloisio et al.), hep-ex/0204012.
4. T. Barnes, hep-ph/0202157.
5. V. V. Anisovich, A. A. Anselm, Ya. I. Azimov, et al., Phys. Lett. 16, 194 (1965); W. E. Tirring, Phys. Lett. 16, 335 (1965); L. D. Soloviev, Phys. Lett. 16, 345 (1965); C. Becchi and G. Morpurgo, Phys. Rev. 140, 687 (1965).