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Intersection Reduction

This technique is exactly the same in Killer as in regular Sudoku. Because this technique is covered in some detail in the Sudoku Solving Techniques section, this is just a brief explanation. You can read about it in the context of regular Sudoku here. The rule for intersection reduction is: if the only place a candidate value can occur in a group is on the intersection with another group, then it can be eliminated from the rest of the intersecting group. Here is an example:

In this example, we can eliminate the candidate "4" from the cells highlighted in red. The digit "4" cannot appear anywhere in the cells highlighted in blue. This means that it must appear in one of the cells highlighted in orange, which are all on the same row. Because there must be a "4" somewhere in these cells, there cannot be a "4" anywhere else on the row, so the red cells cannot contain a "4".

For more examples, and further explanation, refer to Intersection Reduction, in the Sudoku Solving Techniques section.

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