I am especially indebted to Michael Reisenberger, Roberto
DePietri Don Marolf, Jerzy Lewandowski, John Baez, Thomas
Thiemann and Abhay Ashtekar for their accurate reading of the
manuscript, their detailed suggestions and their ferocious
criticisms. Their inputs have been extended and their help
precious. I am grateful to all my friends in the community for
the joy of doing physics together. This work was supported by NSF
Grant PHY-95-15506.