1. E. D. Bloom et al., SLAC-PUB-796, Report presented at the XV International Conference on High Energy Physics, Kiev, USSR, 1970;
2. M. Kendall et al., Report presented at the Cornell Meeting on Electromagnetic Interactions.
3. K. Wilson, Phys. Rev. 179, 1499 (1969).
4. R. Brandt and G. Preparata, Ann.of Phys. 61, 119 (1970).
5. E.D.Bloom and F.J.Gilman,Phys.Rev.Letters 25,1140 (1970);