How do we know that Roberts is writing the opinion?
http://www.freerepublic.com/focus/f-news/2899079/posts?page=242#242
http://minx.cc/?post=330437
http://www.washingtonpost.com/politics/speculation-grows-that-roberts-will-write-majority-opinion-in-health-care-case/2012/06/26/gJQAShqe4V_print.html