1. Mandelstam, S.: Nuovo cimento 30, 1127, 1148 (1963).
2. Glaser, V.: Private communication.
3. Hove, L. van: Lectures at the Seminar on High Energy Physics and Elementary Particles, International Centre for Theoretical Physics of I.A.E.A., Trieste, May–June 1965, to be published
4. Lindenbaum, S. J.: Rapporteur's talk. International Conference on High Energy Physics, Dubna, August 1964
5. Foley, K. J., R. S. Gilmore, R. S. Jones, S. J. Lindenbaum, W. A. Love, S. Ozaki, E. H. Willen, R. Yamada, and L. C. L. Yuan: Phys. Rev. Letters 14, 862 (1965)