1. G. Cosenza, A. Sciarrino andM. Toller:Proceedings of the Topical Conference on the High-Energy Collisions of Hadrons, CERN, vol.2, Geneva, 1968), p. 45.
2. G. Cosenza, A. Sciarrino andM. Toller:Nuovo Cimento,57 A, 253 (1968). In the following this paper is denoted by I.
3. G. Cosenza, A. Sciarrino andM. Toller:Phys. Lett.,27 B, 398 (1968).
4. G. Cosenza, A. Sciarrino andM. Toller: CERN preprint TH.906 (1968). The present paper is an improved version of this unpublished preprint.
5. In order to avoid confusion with other symbols, we indicate byW the Mandelstam variable which is usually denoted byt.