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Pointing Pairs, Pointing Triples, Intersection Removal Strategy

Intersection removal is a strategy where you can eliminiate one candidate from a cell or cells. There are two types of intersection removal: pointing pairs and box/line reduction. This page will deal with the first of those two.

Pointing Pairs and Triples

A pointing pair occurs when a candidate appears twice in a block, and that candidate is also aligned on the same row or column. This means that you know that the candidate MUST occur in one of the two squares in the block, and because of that, you can eliminate that candidate from any other cells in the row or column that the candidate is aligned on.

In the above example, the 2s in red occur twice in the block. Those 2s are also aligned in the same row. Since we know that the 2s must occur in that block, they can't appear elsewhere in that row, so we can cross out any other 2s in that row.

Interactive Example

There is a pointing pair in the following example puzzle. Can you find it?

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Pointing Triples

If a candidate appears only three times in a block, and that candidate is also aligned in the same row or column, it is a pointing triple. You know that the candidate MUST occur in one of those three cells in that block, and because of that, you can eliminate that candidate from any other cells in the row or column that the candidate is aligned on.


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