Sudoku Assistant - The Sudoku Trainer and Solver

Hidden Subset Technique

This technique is somewhat similar to the 'N'-Possible approach, but as we will see, the contributory subset of values that go to make up the set are 'hidden' amongst other candidate values in the region (row, column or subgrid).

The following table shows the candidate values for a possible scenario, with three values in the hidden-subset, in three cells. The values in the subset are {1,3,6}. It may not be immediately obvious, but the three green cells are the only cells in this subgrid that can take those values... it doesn't matter that some of them seem to be able to take other values, or that not all the values are possible in all three cells ({3} is not possible in cell [3,2] for example).

Nevertheless, these three values could only exist on the highlighted cells, so no other values could possibly be on them... so we can remove {8} from cell [1,2] and {4} from cell [3,2].

136 2 7            
1368 5 146            
89 489 489            
                 
                 
                 
                 
                 
                 

You may find a hidden subset for 2, 3 or 4 value sets, and possibly more.

If you are unsure of any of the terminology we use, you may find it helpful to refer to our Glossary.

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