1. KTev Collaboration, A. Alavi-Harati et al., Phys. Rev. Lett. 83 (1999) 22; NA48 Collaboration, V. Fanti et al., Phys. Lett. B 465 (1999) 335.
2. A. Pich, Talk at the Fourth International Conference of Hyperons, Charm and Beauty Hadrons, Valencia, June 2000, hep-ph/0010181.
3. D. Hitlin, Talk at the 30th International Conference on High Energy Physics, Osaka, Japan, July 27–August 2, 2000, hep-ex/0011024.
4. H. Aihara, Talk at the 30th International Conference on High Energy Physics, Osaka, Japan, July 27–August 2, 2000, hep-ex/0010008.
5. CDF Collaboration, T. Affolder et al., Phys. Rev. D 61 (2000) 072005.