1. For a review seeChan Hong-Mo:Proceedings of the XIV International Conference on High-Energy Physics (1968), p. 391.
2. P. Hoyer, B. Peterson, A. T. Lea, J. E. Paton andG. H. Thomas: CERN preprint TH. 1262 (1970). Other references in this preprint.
3. B. Petersson andN. A. Törnqvist:Nucl. Phys.,13 B, 629 (1969).
4. See for instanceV. E. Asribekov:Nucl. Phys.,34, 461 (1962).
5. B. Svensson:Nucl. Phys.,15 B, 93 (1970).