Three cells in a unit share candidates that are subsets of the same three digits.
When three cells in a unit have candidates that together span exactly three digits (each cell holds a subset of those three), those three digits can be eliminated from all other cells in the unit.
Example: {2,5}, {2,8}, {5,8} → All are subsets of {2,5,8} → Eliminate 2, 5, 8 from other cells.
| 2 | 4 | 8 | 9 | 3 | 15 | 15 | 7 | 6 |
| 1 | 3 | 5 | 6 | 7 | 8 | 2 | 4 | 9 |
| 6 | 7 | 9 | 12 | 124 | 145 | 3 | 58 | 18 |
| 3 | 5 | 1 | 7 | 8 | 2 | 9 | 6 | 4 |
| 9 | 8 | 4 | 13 | 6 | 13 | 7 | 2 | 5 |
| 7 | 2 | 6 | 4 | 5 | 9 | 8 | 1 | 3 |
45 | 6 | 2 | 138 | 14 | 1347 | 15 | 9 | 178 |
45 | 9 | 3 | 128 | 124 | 147 | 6 | 58 | 178 |
| 8 | 1 | 7 | 5 | 9 | 6 | 4 | 3 | 2 |
This 9×9 puzzle is solver-verified to require this technique on its solution path.