Department of Computer Science, Brown University, Providence, RI, USA. aritz@cs.brown.edu|Department of Computer Science, Brown University, Providence, RI, USA. aritz@cs.brown.edu|Department of Computer Science, Brown University, Providence, RI, USA. aritz@cs.brown.edu|Department of Computer Science, Brown University, Providence, RI, USA. aritz@cs.brown.edu|Department of Computer Science, Brown University, Providence, RI, USA. aritz@cs.brown.edu