If you’ve ever shuffled a deck of playing cards, you’ve most likely created a unique deck. That is, you’re probably the only person who has ever arranged the cards in precisely that order. Although this claim sounds incredible, it’s a great illustration of how quickly large numbers can creep into everyday situations—with occasionally challenging consequences, as the developers of an online poker game painfully discovered in the late 1990s.The mathematics of card shuffling is quite easy to explai...