Actually, it's probably easy ... I'd just have to reverse time.

Backstory: About 60 years ago, I was chatting with a visiting Indian Guru, when he handed me a deck of cards. He instructed me to deal out the cards in various permutations and patterns, often with intervening cuts or selecting one of several stacks. After a dozen or so of these seemingly random actions, he had me deal out four stacks, each of which turned out to be Ace to King by suits. Then came the lesson: He explained that it had started with a "stacked" deck. He had taken the final dealing, and working the permutations backwards in time, and had so arranged the cards in the deck he had originally handed me. The concept he presented was that rather than strive to understand a problem from a starting condition, assume a theoretical answer and work backwards to the starting point. -Phil