Computer Science Department, Princeton University, 35 Olden Street, Princeton, NJ 08544, USA. mhibbs@cs.princeton.edu|Computer Science Department, Princeton University, 35 Olden Street, Princeton, NJ 08544, USA. mhibbs@cs.princeton.edu|Computer Science Department, Princeton University, 35 Olden Street, Princeton, NJ 08544, USA. mhibbs@cs.princeton.edu|Computer Science Department, Princeton University, 35 Olden Street, Princeton, NJ 08544, USA. mhibbs@cs.princeton.edu