Department of Mathematics, MIT, Cambridge, Massachusetts, United States of America, Computer Science and Artificial Intelligence Laboratory, MIT, Cambridge, Massachusetts, United States of America, Department of Mathematics, UC Berkeley, Berkeley, California, United States of America.|Computer Science and Artificial Intelligence Laboratory, MIT, Cambridge, Massachusetts, United States of America.|Department of Mathematics, MIT, Cambridge, Massachusetts, United States of America, Computer Science and Artificial Intelligence Laboratory, MIT, Cambridge, Massachusetts, United States of America.|Department of Mathematics, MIT, Cambridge, Massachusetts, United States of America, Computer Science and Artificial Intelligence Laboratory, MIT, Cambridge, Massachusetts, United States of America.