1. A. A. Logunov, M. A. Mestvirishvili and Nguen Van Hieu, Phys. Lett.,25B, 611 (1967).
2. A. A. Logunov and Nguen Van Hieu, Topical Conference on High Energy Collisions of Hadrons, CERN, Geneva (1968), p. 74.
3. A. A. Logunov, Nguen Van Hieu, and O. A. Khrustalev, Problems of Theoretical Physics, in: Essays Dedicated to N. N. Bogolyubov on the Occasion of His Sixtieth Birthday, Moscow (1969).
4. G. Tiktopoulos and S. B. Treiman, Phys. Rev.,167, 1408 (1968).
5. H. Epstein, Topical Conference on High Energy Collisions of Hadrons, CERN, Geneva (1968), p. 190.