[1] Microsoft, One Microsoft Way, Redmond, WA 98052 USA
[2] Microsoft Res New England, Cambridge, MA 02142 USA
[3] Cornell Univ, Comp Sci Dept, Ithaca, NY 14853 USA
[4] NYC, Res Grp, Google Inc, New York, NY USA
[5] Boston Univ, Dept Comp Sci, Boston, MA USA