Microsoft Research, Redmond, Washington, United States of America. jennl@microsoft.com|Microsoft Research, Redmond, Washington, United States of America. jennl@microsoft.com|Microsoft Research, Redmond, Washington, United States of America. jennl@microsoft.com|Microsoft Research, Redmond, Washington, United States of America. jennl@microsoft.com|Microsoft Research, Redmond, Washington, United States of America. jennl@microsoft.com|Microsoft Research, Redmond, Washington, United States of America. jennl@microsoft.com|Microsoft Research, Redmond, Washington, United States of America. jennl@microsoft.com|Microsoft Research, Redmond, Washington, United States of America. jennl@microsoft.com