1. V. De Alfaro, S. Fubini, G. Furlan andC. Rossetti: preprint, Torino (Dec. 1966).
2. V. De Alfaro, S. Fubini, G. Furlan andC. Rossetti:Phys. Lett.,21, 576 (1966);R. F. Dashen andM. Gell-Mann:Proc. of the Third Coral Gables Conference on Symmetry Principles at High Energies, University of Miami (1966).
3. This result is proved in ref. (1)V. De Alfaro, S. Fubini, G. Furlan andC. Rossetti: preprint, Torino (Dec. 1966). in the case of spin-flip pion-nucleon scattering without charge exchange. In the case of charge exchange the proof fails; however the saturation in terms of a finite number of resonances, if even possible, appears to give a physically unacceptable solution. This point is commented further in Sect. 2 on a specific example.
4. R. F. Dashen andM. Gell-Mann:Phys. Rev. Lett.,17, 340 (1966) and lecture notes given at the 1966 International School of Physics “Ettore Majorana”, Erice (1966).
5. We acknowledge interesting discussions with Prof.B. Sakita on the difficulties encountered in the case of nondegenerate masses.