David Whitehead (modified translation; added keyword) on 1 March 2001@09:04:32. David Whitehead (added note; modified keywords) on 17 July 2002@10:53:05. Nicholas Fincher (Added some details) on 6 July 2003@06:05:19. David Whitehead (expanded note) on 2 August 2011@05:16:34.