## Eternity puzzle
Early on, Selby and Riordan made a surprising discovery. As the number of pieces in an Eternity-like puzzle increased, so did the difficulty – but only up to a point. The critical size is about 70 pieces, which would be almost impossible to solve. For larger puzzles, however, the number of possible correct solutions increases. In the case of Eternity itself, with its 209 pieces, there are thought to be at least 10 ^{95} solutions
– far more than the number of subatomic particles in the universe
but far, far less than the number of non-solutions. The puzzle itself is
much too large to solve by an exhaustive search but not, as it turns out,
by more savvy methods that take into account what shaped regions are easiest
to tile and what shaped pieces are easiest to fit. By steadily refining
their search algorithm, Selby and Riordan were able to prune out the vast
majority of non-solutions and, with a bit of good fortune, to hit upon a
correct solution and claim the prize. ## Related categories• GAMES AND PUZZLES• TILINGS | |||||||

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