You’re down to the last four squares of an expert Kakuro. You try one fill and every clue checks out. You erase it, try the other, and every clue checks out again. Your pencil hovers. One of them has to be wrong, and the puzzle has stopped giving you hints.

So you pick one. If you’re …

Your first Kakuro grid looks like a crossword someone forgot to finish. Black squares are slashed with diagonal lines, small numbers sit in their corners, and rows of empty white boxes wait for you. You pick the first clue you see, a 15 across three cells, and start trying combinations. 9, 5, 1? 8, …

You found the 3 in the corner of your Kakuro grid. Two cells, so it’s a 1 and a 2. You penciled both digits into both cells and felt good about it. Now you’re staring at those two cells, pencil hovering, and the question is simple: which one gets the 1?

You could flip a coin. Half the …