Swordfish

Swordfish is another advanced technique which can eliminate certain candidates from squares. We are looking for three rows (or columns) that contain up to three of a particular number in the same relative position. Although Swordfish are an extension of X-Wings, not all of the squares have to contain the number in question.

Using 'Show squares with a...' and selecting <8>, we can see that R3, R5 & R7 contain up to three lots of <8> in the same relative position. So the <8> might be in R3C7, R5C8 & R7C3 or R3C8, R5C3 & R7C7 or some other combination. Although we don't know which way around <8> goes, we do know that all other <8> from C3 can be removed because the <8> is in either R5C3 or R7C3. Similarly, all other <8> from C7 and C8 can be removed.