Indirect Hidden Single

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An indirect hidden single also requires candidates to be filled in on the grid first. Then you inspect the candidates within a house (row, column, or box). If one candidate appears only once in that house, then the cell containing it must be filled with that digit.

For example, look at candidate 4 in row 5 of the grid below. It appears only once in that row, so R5C1 must be 4. Also, this cannot be seen by cross-hatching alone, because the candidate 4 in R5C9 was actually removed by another technique, namely the naked pair of {1,4} in R1C9 and R2C9.

An indirect hidden single can also appear in a column or a box. For example, in column 3 of the grid below, candidate 8 appears only in R3C3, so R3C3 must be 8. Likewise, this can only be seen after candidates have been filled in, because the candidate 8 in R2C3 was removed by another technique.

As another example, in box 7 of the grid below, candidate 2 appears only once in R8C2, so R8C2 must be 2.