Sword-Fish

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Sword-Fish
The Sword-Fish technique is based on the same principles as the X-Wing technique. The difference is that while the X-Wing is formed by two by two cells, the Sword-Fish is formed by three by three cells. In the puzzle below, we have an example of the Sword-Fish technique.

A Sword-Fish pattern is formed by:
  • three rows each containing no more than three cells with a specific candidate value sharing the same column.
  • three columns each containing no more than three cells with a specific candidate value sharing the same row.
These cells form a grid of nine cells which are the only possible locations for the candidates in these three rows and columns. In the example, the yellow cells indicate a Sword-Fish. We do not know which cells from the Sword-Fish are a 1, but we do know that cells outside the Sword-Fish that share the same columns cannot be a 1. In the example below, we can exclude the candidate value 1 from the blue cells.
Sword-Fish
In the example below three columns have candidate 5 in no more than three cells. Therefore candidate 5 can be excluded from all other cells in the row. These are the blue cells.
Sword-Fish