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Hidden One

The Hidden One method is the second of the two basic methods. It is as simple as the Naked One and very easy to see with a little practice.

Each field belongs to three logical units: row, column and block.
As we know, each number must occur exactly once in each logical unit. If a number appears as a candidate in only one field of a logical unit, then this number must be entered there, of course, because it would otherwise be "lost" in this logical unit.

The 9 in the yellow box cannot be a candidate anywhere else in the column.
Blocked by z2/s2 and z9/s1.

The 3 in the green field cannot be a candidate anywhere else in the block.
Blocked by z2/s6.

The 7 in the pink box cannot be a candidate anywhere else in the line.
Blocked by z4/s8.
It is also a candidate in only one field in the block.
Blocked by z4/s8 and z6/s2.

In the picture, there are many more Hidden Ones.

The Hidden One is a special case of the Hidden groups.

Sudoku example hidden One

see also: Generalization : Hidden groups



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