Exposed Pair Logic

Sometimes called “Naked Pair,” this is a form of what graph theorists refer to as Chain Exclusion. If, for any given row, column or box, you have a pair of cells with only two matching numbers, you can eliminate any other occurrences of those numbers in the same row, column or box.

Say, for example, that numbers 2 and 4 are the only candidates in the third and sixth cells of a given row. Because there aren’t any other options in either of the two cells, the 2 and 4 couldn’t be candidates elsewhere in that row. See the partial puzzle below.

You can see in the graphic above that because 2 and 4 are the only residents of the third and sixth cells, they don’t belong anywhere else in that row, and “extras” can be safely erased. See the resulting row below.