1. D. J. Herndon, P. Söding, and R. J. Cashmore, Phys. Rev. D11, 3165 (1975).
2. See also B. H. Brandsen and R. G. Moorhouse, The Pion-Nucleon System (Princeton University Press, Princeton, New Jersey, 1973). These authors give a detailed list of earlier references.
3. R. Aaron and R. D. Amado, Phys. Rev. Lett. 31, 1157 (1973). The “minimal” equations which implement both unitarity and subenergy analyticity have been discussed by I.
4. J. R. Aitchison, Phys. Rev. 137, B1070 (1965).
5. R. Aaron and R. D. Amado, Phys. Rev. D13, 2581 (1976).