Department of Mathematics, Harvard University, Cambridge, Massachussetts 02138
Date: January 22, 2002
Department of Mathematics, Harvard University, Cambridge, Massachussetts 02138
Key words and phrases: Birch and Swinnerton-Dyer conjecture, modular abelian variety, visibility, Shafarevich-Tate groups
1991 Mathematics Subject Classification: Primary 11G40; Secondary 11F11, 11G10, 14K15, 14H25, 14H40.