1. H1 Collaboration; T Ahmedet al, Nucl. Phys. B429, 477 (1994)
2. S Aidet al, Nucl. Phys. B470, 3 (1996)
3. ZEUS Collaboration; M Derricket al, Phys. Lett. B315, 481 (1993);Z. Phys. C69, 607 (1996)
4. A Donnachie and P V Landshoff,Nucl. Phys. B231, 189 (1983);B244,322 (1984);B267, 690 (1986);Phys. Lett. B296, 227 (1992);B202, 131 (1988)
5. M Gluck, E Reya and A Vogt,Z. Phys. C67, 433 (1995)