sudokUI › Sudoku techniques › Twinned XY-Chains
Twinned XY-Chains in sudoku
Six cells where two rows cross three columns, or the reverse, holding exactly six different digits as candidates between them, with each digit's pattern cells all seeing each other.
Why it works
Each digit can fill at most one pattern cell, yet six cells need six digits, so every digit is used exactly once. Any of the six digits, X, is removed from every cell outside the pattern that sees all pattern cells containing X.
How to spot it
Find three bivalue cells in one row or column that share a digit, then test a parallel row or column for the other three cells.
Not implemented in sudokUI: the chain engines already find everything it can.
In a puzzle's rating
Each time the solver needs Twinned XY-Chains, the puzzle's difficulty rating grows by 300. Its class is Unfair. How the rating works.
More chains and loops
Remote Pair · Chute Remote Pair · X-Chain · X-Cycles (loops) · Grouped X-Cycles · XY-Chain · Nice Loop · Grouped Nice Loop · Alternating Inference Chain · AIC with Groups · AIC with ALSs