1. Delbourgo R., Rashid H. A., Salam A., Strathdee J.: Proceedings of the Seminar on High Energy Physics and Elementary Particles, Trieste 1965.
2. Rühl W.: Proceedings of the Seminar on High Energy Physics and Elementary Particles, Trieste 1965.
3. Fronsdal C: Proceedings of the Seminar on High Energy Physics and Elementary Particles, Trieste 1965.
4. Delbourgo R., Salam A., Strathdee J.: Proc. Roy. Soc.289 A (1966), 177.
5. Rühl W.: Nuovo Cim.44 A (1966), 572.