Impossible?In Nonplussed!, popular math writer Julian Havil delighted readers with a mind boggling array of implausible yet true mathematical paradoxes. Now Havil is back with Impossible?, another marvellous medley of the utterly confusing, profound, and unbelievableand all of it mathematically irrefutable. Whenever Forty second Street in New York is temporarily closed, traffic doesn't gridlock but flows more smoothlywhy is that? Or consider that cities that