1. A. Martin:Nuovo Cimento,42, 930 (1966).
2. A. Martin andY. S. Jin:Phys. Rev.,135, B 1375 (1964).
3. A. Martin andY. S. Jin:Phys. Rev.,135, B 1369 (1964).
4. G. Roepstorff andJ. L. Uretsky (Argonne, June 1966), and one byY. S. Jin (Brown University) which also establish threshold behaviour. However, in both papers, as well as in ours, some assumptions are made to get the normal threshold behaviour. In the first one, one assumes that the off-shell amplitude is finite atE=E threshold, and in the second one that the absorptive part inside the extended large Lehmann ellipse stays finite as one approaches threshold.
5. L. Lukaszuk andA. Martin:Phys. Lett.,21, 96 (1966).