sudokUI › Sudoku techniques › XY-Wing
XY-Wing in sudoku
Y-Wing · bent triple · 3-cell XY-Chain · how it fits
A bivalue pivot cell with candidates X and Y sees two bivalue pincer cells, one with candidates X and Z, the other with candidates Y and Z.
Why it works
If the pivot is X, the pincer with X becomes Z; if the pivot is Y, the pincer with Y becomes Z. At least one pincer is therefore Z, so Z is eliminated from every other cell that sees both pincers.
How to spot it
From a bivalue cell, scan the bivalue cells it sees for two that split its digits between them and share one new digit.
Worked example
XY-Wing: pivot r7c7 (79) with pincers r7c6 (76) and r8c9 (96); one pincer must be 6, so 6 is removed from cells seeing both. So 6 is removed from r7c8, r8c6.
Practise it on a real puzzle. sudokUI generates a puzzle that needs XY-Wing 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 XY-Wing, the puzzle's difficulty rating grows by 160. Its class is Hard. It is needed in 1 in 16 puzzles that sudokUI generates. How the rating works.