Sudoku FlowSudoku technique lessons / XY-Chain
Lesson 25
XY-Chain
The rule
In an XY-chain, the links force at least one of its two ends to hold their shared candidate, so any cell that sees both ends loses it.
Step by step
- These 4 cells each hold just two candidates, and both end cells hold 3. Suppose the first end is not 3: then it is 5. Each link hands the next cell its other candidate (7, 2), so the last end is 3. Either way, one of the two ends is 3.
- At least one end must be 3, so we can remove the candidate 3 from any other cell that sees both ends.
Try it on more boards
Each board is a real puzzle from our app, at a moment where XY-Chain applies. Find the step yourself, or tap Hint and the app's own hint walks you through it.
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