 The puzzle was solved on May 15, 2000, before the first deadline, by two Cambridge mathematicians, Alex Selby and Oliver Riordan.Key to their success was the mathematical rigour with which they approached the problem of determining the tileability of individual pieces and of empty regions within the board.These provided measures of the probability that a given piece could help to fill or 'tile' a given region, and the probability that a given region could be tiled by some combination of pieces.