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 X-Wing An X-Wing is a advanced technique which can eliminate certain candidates from squares. Its name comes from the pattern formed by the numbers. We are looking for two rows (or columns) that contain exactly two of a particular number. Using 'Show squares with a...' and selecting <4>, we can see that both R3 & R7 contain two lots of <4>. So the <4> might be in R3C2 & R7C8 or R3C8 & R7C2. Although we don't know which way around <4> goes, we do know that all other <4> from C2 can be removed because the <4> is in either R3C2 or R7C2. Similarly, all other <4> from C8 can be removed. Using 'Show squares with a...' and selecting <1>, we can see that both C3 & C7 contain two lots of <1>. So the <1> might be in R3C3 & R9C7 or R3C7 & R9C3. Although we don't know which way around <1> goes, we do know that all other <1> from R3 can be removed because the <1> is in either R3C3 or R3C7. Similarly, all other <1> from R9 can be removed.