Fri, 11 Feb 2011 13:30:37 +0000 urbanc included comments by Xingyuan
Fri, 11 Feb 2011 12:13:35 +0000 urbanc slightly streamlined the proof
Thu, 10 Feb 2011 21:00:40 +0000 urbanc simplified a bit the proof
(0) -30 -10 -3 +3 +10 +30 +100 tip