1. Proceedings of the Argonne Conference on ππand πKInteractions (Argonne, 1969). Earlier references can be found in this book.
2. Proceedings of the XV International Conference on High-Energy Physics (Kiev, 1970).
3. E. Malamud andP. E. Schlein:Proceedings of the Argonne Conference on ππand πKInteractions (Argonne, 1969), p. 107.
4. J. P. Baton, G. Laurens andJ. Reignier: preprint CEN-Saclay, submitted toPhys. Lett. B (September 1970).
5. S. Weinberg:Phys. Rev. Lett.,17, 616 (1966);J. Iliopoulos:Nuovo Cimento,52 A, 192 (1967);53 A, 552 (1968).