Mo, Tara and Dior

Mo went first, because Mo's step was the simplest and the most foundational of them all: run the rule forward.

Mo held up a rule everyone agreed on. "If it rains, the ground gets wet." Then Mo held up a fact. "It is raining." And then Mo took the one honest step forward, and it landed on solid stone. "Therefore — the ground is wet."

That was it. That was the whole move. "People think it's too simple to matter," Mo said. "But watch how sturdy it is. If the rule really holds — if it rains, the ground gets wet — and the start is really true — it is raining — then the ending cannot be false. It's forced. The ground must be wet. I'm not guessing. I'm just walking the rule forward one honest step, and the ground catches me every time."

Then Tara stepped up, and did the same rule the other direction — the move that surprises people.

"Same rule," said Tara. "If it rains, the ground gets wet." But this time Tara didn't start at the beginning. Tara started at the end, with a fact about the ending: "The ground is not wet." And then Tara walked the rule backward. "If rain always makes the ground wet — then a dry ground means it cannot have rained. Therefore — it did not rain."

"This one feels like magic the first time," Tara admitted, "but it isn't. It's just the same rule, read backward. If the rule promises that P leads to Q, then no Q means there was no P — because if there had been, Q would have happened. The dry ground proves it didn't rain. I don't need to have seen the sky. The rule and the ending tell me for certain."

And then came Dior, whose step worked when you didn't have a rule at all — just a list, and a way to shrink it.

"The vase got knocked over," said Dior, laying out the puzzle. "Either the cat did it, or the dog did it." Two possibilities. Then Dior found one honest fact: "The cat was shut outside all afternoon. It was not the cat." And Dior crossed it off — and with the cat gone, only one branch remained, and it had to be true. "Therefore — it was the dog."

"Cross off what it isn't," said Dior, "and whatever's left standing has to be it. That's my whole move. I don't have to catch the dog in the act. I just have to be sure of the list — either the cat or the dog — and sure of one thing it isn't. Take away the false one, and the true one is all that's left. The answer was hiding in the list the whole time. I just cleared away everything it couldn't be."