The world of mathematics is in uproar over rumours that its most prestigious prize will be turned down next week by one of its brightest stars. The Fields Medal, the equivalent of a Nobel Prize in mathematics, is awarded every four years to young mathematicians who have made the biggest impact in their fields. It is due to be presented by the King of Spain in a ceremony in Madrid on Tuesday 22 August. But Gregori Perelman, who has been widely tipped to receive it, has resigned his post at the Steklov Institute of Mathematics in St Petersburg, Russia, and...