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