1. G. F. Chew andF. E. Low:Phys. Rev.,115, 1640 (1959).
2. R. Ascoli andA. Minguzzi:Phys. Rev.,118, 1435 (1960).
3. The cross section for anelastic processes below threshold would have some interest in connection with the dispersion relations for such processes (private communication ofA. Minguzzi).
4. Of course these singularities are due to the one particle states of massμ 1. Hereμ 1 is the nucleon mass, so we expect that the singularities due to two particle states (one nucleon an one meson) will also be very near to the physical range ofΔ 2. (This remark is due toA. Minguzzi).
5. R. Karplus, C. M. Sommerfield andE. H. Wichmann:Phys. Rev.,114, 376 (1959).