Naked Pairs

What is a naked pair?

A naked pair is two cells in the same row, column, or box that contain exactly the same two candidates, and nothing else. One of the cells will hold the first digit and the other cell the second digit. You do not know which way round yet, but you do know that no other cell in that unit can contain either digit.

How to use a naked pair

1. Fill in candidates for the empty cells of a row, column, or box.
2. Look for two cells with the same two candidates, such as {4, 7} and {4, 7}.
3. Eliminate. Remove those two digits from every other cell of the same unit. If the pair is also inside one box, remove them from that box as well.

In the example, the cell in column 3 drops from {1, 4, 7, 9} to {1, 9}, column 6 becomes {1, 3}, and column 8 becomes {3, 9}. Those smaller lists often create new singles right away.

Naked triples

The same idea works with three cells whose candidates, taken together, include only three digits, for example {2, 5}, {5, 8}, and {2, 8}. Each cell does not need all three digits. Those three digits are locked into the three cells, so you can remove them from the rest of the unit.