submission deadline: January 15, 2014
  1. December 29, 2013 paper
  2. December 31, 2013 paper
  3. January 14, 2014 paper
  4. May 6, 2014 paper with an attempt to resolve the undefined Δ
  5. May 16, 2014 paper with incorporated comments by the Editor
  6. May 21, 2014 paper