1. R.G. Roberts, The structure of the proton, Cambridge University Press 1990
2. J.P. Ralston and D.E. Soper, Nucl. Phys. B152 (1979) 109.
3. R.D. Tangerman and P.J. Mulders, Phys. Rev. D51 (1995) 3357.
4. D.E. Soper, Phys. Rev. D 15 (1977) 1141; Phys. Rev. Lett. 43 (1979) 1847.
5. R.L. Jaffe, Nucl. Phys. B 229 (1983) 205.