SECOND HALF OF EXERCISES, PAGES 81 thru 100 A second edition of this book has been published: W. H. Freeman and Company, New York, 1992, ISBN 0 7167 2327 1 A treatment of general relativity by the same authors: Exploring Black Holes Introduction to General Relativity Addison Wesley, San Francisco, 2000, ISBN 0 201 38423 X