No-show is a problem

Grigory Perelman, the Russian academic credited with solving one of the toughest problems in mathematics, has declined the maths equivalent of the Nobel Prize. Professor Perelman, who claimed to have solved the century-old Poincaré problem in 2002, was to have collected a Fields Medal in Madrid this week, but chose not to accept it.

Three other winners accepted their prizes: Andrei Okounkov of the University of California, Berkeley; Terence Tao of the University of California, Los Angeles; and Wendelin Werner of the University of Paris-Sud.