| Sun, 13 Feb 2011 10:36:53 +0000 | zhang | More into the second direction | file | diff | annotate |
| Fri, 11 Feb 2011 13:30:37 +0000 | urbanc | included comments by Xingyuan | file | diff | annotate |
| Fri, 11 Feb 2011 12:13:35 +0000 | urbanc | slightly streamlined the proof | file | diff | annotate |
| Thu, 10 Feb 2011 21:00:40 +0000 | urbanc | simplified a bit the proof | file | diff | annotate |