Sudoku Solving Techniques - Hidden Single

This technique is also known as "unique candidate."

If a cell is the only one in a row, column or block that can take a particular value, then it must have that value. This is because all rows, columns and blocks, must contain each of the digits 1 to 9.

For example, in the partial puzzle below, the marked cell is the only one in block five that can hold a 2, and so it must hold a 2.

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