XY-Chain
Advanced Logic30 / 32A domino run through bivalue cells.
String together cells that each hold exactly two candidates, where every link passes a shared digit to the next cell. If both chain ends contain the same digit Z, denying Z at one end starts a domino run that forces Z at the other.
So Z is guaranteed at one end or the other — and any cell that sees both ends can cross Z off. The chain can wander across the whole board.
See it in action
Step 1 of 4
The setup
Bivalue-heavy boards are XY-Chain country. Start at a bivalue cell, follow shared candidates from cell to cell, and watch for another cell that closes the loop on your starting digit. Step through this real position to see it happen.
Practice
Trace the XY-Chain and remove the shared end digit from cells seeing both chain ends.
Drill 1 of 29Tap a cell, then the candidate digit you want to remove.