Originally Posted by Bob

When is a proof a proof?
A Russian mathematician named Perelman recently solved a problem in topology called Poincare's conjecture which was over a hundred years old. The proof is very sophisticated and is published in a 473 page book, so reviewing it for correctness is not trivial. An organization called the Clay Institute will award Dr Perelman its lucrative millenium prize after the proof has been public for two years without successful challenge.