1. W. H. Barkas and D. M. Young, UCRL-2579 (1954).
2. D. A. Galstyan, G. B. Zhdanov, M. I. Tret’yakova, M. N. Shcherbakova, and M.M. Chernyavskii, Zh. Éksp. Teor. Fiz., 51:417 (1966) [Sov. Phys. — JETP, 24(2): 280 (1967)].
3. P. Dodd, M. Jobes, J. Kinson, et al., Aix-en-Provence Intern. Conf. on Elementary Particles, 1:433 (1961).
4. M. Bardadin, L. Michejda, S. Otwinowski, and R. Sosnowski, Preprint N 511/VI, Warsaw (1964).
5. B. Jordan, CERN, 65–14, Geneva (1965).