The Kakuro book said “Expert.” You believed it for the first ten minutes, while the corners filled in nicely. Now you’re looking at a block in the middle of the grid where every clue has five ways to be right, your pencil marks are three deep, and the eraser has worn a soft gray …

You’ve hit a wall in an expert Kakuro. Every magic block on the page is filled in, every easy crossing is done, and a fat block of empty cells is sitting in the middle of the grid. Each clue around it has five or six workable combinations. You pencil a few, erase them, and pencil them again. …

A fresh Kakuro grid sits in front of you, every white cell empty. Your eye lands on a 27 running across five cells, so you start there. 9, 8, 6, 3, 1? 9, 7, 5, 4, 2? 8, 7, 6, 4, 2? All valid. There are eleven different digit sets that add to 27 in five cells, and nothing yet tells you which one is …