Department of Computer Science, Stanford University, Stanford, CA 94305, USA. brudno@cs.stanford.edu|Department of Computer Science, Stanford University, Stanford, CA 94305, USA. brudno@cs.stanford.edu|Department of Computer Science, Stanford University, Stanford, CA 94305, USA. brudno@cs.stanford.edu|Department of Computer Science, Stanford University, Stanford, CA 94305, USA. brudno@cs.stanford.edu|Department of Computer Science, Stanford University, Stanford, CA 94305, USA. brudno@cs.stanford.edu