David Whitehead (added note; cosmetics) on 17 June 2003@11:17:52. Catharine Roth (added keyword and cross-references) on 21 September 2006@00:22:48. Catharine Roth (another keyword) on 21 September 2006@10:56:38. David Whitehead (another keyword) on 10 May 2011@06:55:59. David Whitehead (tweaking) on 1 January 2014@03:49:11. David Whitehead (coding) on 26 May 2016@08:23:55.