Computer Science Department, Stanford University, Stanford 94305, USA. eran@cs.stanford.edu|Computer Science Department, Stanford University, Stanford 94305, USA. eran@cs.stanford.edu|Computer Science Department, Stanford University, Stanford 94305, USA. eran@cs.stanford.edu|Computer Science Department, Stanford University, Stanford 94305, USA. eran@cs.stanford.edu|Computer Science Department, Stanford University, Stanford 94305, USA. eran@cs.stanford.edu