1. Sudarshan, E. C. G., and Marshak, R. E., Proc. Padua-Venice Conf., Mesons and Newly Discovered Particles, 1957; reprinted in Development of the Theory of Weak Interaction Theory (edit. by Kabir, P. K.) (Gordon and Breach, 1963).
2. Feynman, R. P., and Gell-Mann, M., Phys. Rev., 109, 193 (1958).
3. Gerstein, S. S., and Zeldovich, Ya. B., Zhur. Eksper. Teoret. Fiz. USSR 29, 698 (1955) (translation: Soviet Physics. JETP 2, 576 (1957)).
4. Weisberger, W. I., Phys. Rev. Lett., 14, 1051 (1965).
5. Review by Pinski, G., Sudarshan, E. C. G., and Mahanthappa, K. T., in Proc. Thirteenth Intern. Conf. High Ener. Phys., Berkeley (1966).