Mirrored from Sudopedia, the Free Sudoku Reference Guide

Naked Subset

A Naked Subset is formed by N cells in a house with candidates for exactly N digits.

N is the size of the subset, which must lie between 2 and the number of unsolved cells in the house minus 2. Since every Naked Subset is complemented by a Hidden Subset, the smallest of both sets will be no larger than 4 in a standard sized Sudoku.

An alternative name for Naked Subset is Number Chain, but this term is not used very often.

Names for Different Sizes

Naked Pair
Size 2
Naked Triple
Size 3
Naked Quad
Size 4

Recognition

To recognize a Naked Subset, you probably need pencilmarks, unless you have a very good memory. A naked pair is easy to locate because you only need to spot two cells with candidates for the same two digits. A naked triple is more difficult to recognize, because not all three cells need to contain candidates for all three digits. Subsequently, a naked quad is even more difficult to spot.

When all cells are located in an intersection, spotting the subset is much easier. Because there are only 3 cells in an intersection, it is not possible to find Naked Quads in an intersection. The subset can cause eliminations in both intersecting houses. A size 2 is called a Locked Pair and size 3 is a Locked Triple.

See Also

This page was last modified 12:13, 13 June 2007.