1. See, for instance,H. Burkhardt: inProceedings of the Triangle Seminar (Smolenice, 1973), to be published by the Slovak Academy of Sciences, CERN Preprint TH. 1784 (1974).
2. D. Atkinson, P. W. Johnson andR. L. Warnock:Comm. Math. Phys.,28, 133 (1972).
3. H. Burkhardt:Nuovo Cimento,10 A, 379 (1972).
4. For example,P. D. B. Collins andE. J. Squires:Regge Poles in Particle Physics (Berlin, 1968), Chap. 6.
5. It is well known (5) that elastic unitarity gives a unique set of partial-wave amplitudes at energies near threshold which can then be continued in energy; however, we know of no sound effective way in practice of using this as a constraint to remove the continuum ambiguity at higher energies, because of the inherent instability of numerical analytic continuation.