Techniques · Expert

XY-wing

An XY-wing is three cells, each with exactly two candidates. One cell, the pivot, sees the other two, the wings. The pivot's two digits are split across the wings: one wing shares the first digit, the other wing shares the second, and the wings share a third digit with each other.

Whatever the pivot is, one of the wings is that third digit. A cell that can see both wings therefore can't be the third digit, and it loses it. The wings do not have to see each other.

When it shows up

XY-wings are Expert. A puzzle that needs one is past pairs, triples, and quads.

XY-wings do not appear in the 1,483 NYT puzzles. That set never goes beyond triples.

See it on a real puzzle

The marks are the candidates left when this is the next step in the solve. Step through it: the pattern, what leaves, and what that forces.

See the pattern

Look at these three cells.

6
2
8
5
7
9
1
5
3
8
1
7
2
6
7
1
8
5
7
1
5
4
2
6
3
3
8
6
2
5
7
1
9
4
2
4
9
6
3
1
5
7
8
8
4
7
5
1
2
1
2
5
7
5
6
7
1
8
9

Play a puzzle that needs this

Related

XY-chainNaked pair