1. Jaffe, R.L., Low, F.E.: Phys. Rev. D19, 2105 (1971)
2. Simonov, Yu.A.: Phys. Lett.107B, 1 (1981)
3. Mulders, P.J.: Phys. Rev. D25, 1269 (1982); ibid. D26, 3039 (1982); ibid. D28, 443 (1983)
4. Lomon, E.L.: Nucl. Phys. A434, 139c (1985)
5. Aerts, A.T. et al.: Phys. Rev. D17, 260 (1978)