Department of Computer Science, Duke University, Durham, NC 27708, USA. lee@cs.duke.edu|Department of Computer Science, Duke University, Durham, NC 27708, USA. lee@cs.duke.edu|Department of Computer Science, Duke University, Durham, NC 27708, USA. lee@cs.duke.edu|Department of Computer Science, Duke University, Durham, NC 27708, USA. lee@cs.duke.edu