Department of Computer Science, Columbia University, New York, New York, United States of America.|Department of Computer Science, Columbia University, New York, New York, United States of America.|Department of Computer Science, Columbia University, New York, New York, United States of America.|Department of Computer Science, Columbia University, New York, New York, United States of America.|Department of Computer Science, Columbia University, New York, New York, United States of America.|Department of Computer Science, Columbia University, New York, New York, United States of America.|Department of Computer Science, Columbia University, New York, New York, United States of America.