sudokUI › Sudoku techniques › Remote Pair
Remote Pair in sudoku
XY-Chain of one pair · how it fits
A chain of at least four bivalue cells that all hold the same two candidates X and Y, each cell seeing the next.
Why it works
Neighbouring chain cells must differ, so the chain alternates between X and Y. A cell outside the chain that sees two chain cells an odd number of steps apart sees one X and one Y, so X and Y are both removed from it.
How to spot it
Find four or more bivalue cells holding the same two candidates, link those that see each other, and colour the chain alternately.
Worked example
Remote Pair: the cells r2c3, r2c5, r3c4, r5c5, r6c4 form a chain of 35 pairs; cells seeing both "colors" of the chain lose 3 and 5. So 3 is removed from r6c3.
Practise it on a real puzzle. sudokUI generates a puzzle that needs Remote Pair and takes you straight to the position where it applies. Hints draw the pattern on the board and explain the step.
In a puzzle's rating
Each time the solver needs Remote Pair, the puzzle's difficulty rating grows by 110. Its class is Hard. It is needed in 1 in 46 puzzles that sudokUI generates. How the rating works.
More chains and loops
Chute Remote Pair · X-Chain · X-Cycles (loops) · Grouped X-Cycles · XY-Chain · Twinned XY-Chains · Nice Loop · Grouped Nice Loop · Alternating Inference Chain · AIC with Groups · AIC with ALSs