How it works

Look at the two or three empty cells where a row (or column) meets a box. Together they must hold at least two more digits than they have cells. Now find a set of cells elsewhere in the line, and another elsewhere in the box, each using only digits from the crossing and not sharing any with each other.

If the crossing, the line cells and the box cells together have exactly as many cells as there are digits in the crossing, they must between them hold every one of those digits. So the line cells’ digits are confined to the line cells and the crossing, and can leave the rest of the line. The box cells’ digits can leave the rest of the box. Any digit that only the crossing can hold leaves both.

How to spot it

Pick a spot where a row and a box meet with two or three empty cells and many notes between them. Look for a two-note cell in the line and one in the box whose digits split the crossing’s notes between them.

A worked example

This is a step from a real puzzle, a moment where the next move needs a Sue de Coq.

P are the cells where the line crosses the box; A are the cells in the line, B the cells in the box. Struck-through digits are the ones that can be removed.

R1C6, R3C6 (where column 6 crosses box 2) hold 5 digits (1, 2, 5, 7, 8) in just 2 cells. R9C6 in the line hold only 1, 8 and R2C5, R3C4 in the box hold only 2, 5, 7. That makes 5 cells for exactly 5 digits, so between them they hold every one of 1, 2, 5, 7, 8. The 1, 8 must be in the line cells or the crossing, the 2, 5, 7 in the box cells or the crossing. Remove them from the rest of the line and box respectively.

Where it fits in Rocksled Sudoku

Puzzles that need a Sue de Coq are never rated below Expert. Each step of this kind adds 80 points to a puzzle’s difficulty score. When you ask for a hint that needs it, the game names the technique and shows the cells involved. See how to play for the rest of the controls.

Play Sudoku