1st ed., May 6, 1999 2nd ed., August 18 1999 3rd ed., November 23 1999 4th ed., December 28 1999 5th ed., August 18 2000 6th ed., October 30 2001 7th ed., September 20 2002 8th ed. November 17 2003, Update: March 2004 9th ed. May 2004 10th ed. June 2004 All rights reserved Francesco Dell'Orso, Perugia (Italy) dellorso@unipg.it