Decabit Software
Naked Subset

If there are N cells in one unit that contain N candidates between them, then the candidates can be removed from all the other cells in the unit.

Consider the sudoku below.

3
4
5 9
6
7
6
7
2 1 8

In the center block, the cells r4c6 and r5c6 have exactly two candidates, 6 and 7, between them. So we can remove the candidates 6 and 7 from all other cells in the center block. Notice that we could also apply this rule to column 6.

Common names for values of N:
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Last Updated: 8/5/2017 12:27:29 PM CST