David Whitehead (added note and keyword; cosmetics) on 17 June 2001@06:58:34. Catharine Roth (added cross-reference, raised status) on 13 September 2005@23:00:21. David Whitehead (expanded note) on 11 February 2012@08:54:36. Catharine Roth (typo) on 12 March 2012@23:36:47. David Whitehead on 14 June 2015@09:45:34.