X-Wing
xWing
LevelNot seen in a hint yet
How it works
If, on two rows, a digit can only go in the same two columns, those four cells form a rectangle. The digit needs one cell on each row and has only two columns available, so it ends up on one diagonal of the rectangle.
Which diagonal is unknown, but that the two columns are used up is certain, so the digit is removed from the rest of those columns. The four linked cells look like an X, hence the name (wing = the arms), and it works identically with rows and columns swapped.
Worked example
9
1
4
2
5
7
3
4
3
7
5
1
5
3
1
8
4
9
2
4
8
3
5
1
6
3
6
1
4
8
5
2
1
5
6
8
3
4
5
6
1
8
3
1
8
3
2
9
5
8
3
9
5
6
1
● evidence✕ eliminated★ confirmed
In column 2, column 4, 7 can only go in row 6, row 7 — the four cells R6C2, R7C2, R6C4, R7C4 (marked ●).
Two of those four cells take 7, so it is removed from the other 3 cells of row 6, row 7 (✕).
Examples I encountered
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