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.
| 7 | 5 | 14 | 8 | 6 | 2 | 3 | 9 | 1 |
| 3 | 6 | 24 | 9 | 1 | 7 | 8 | 5 | 2 |
| 8 | 9 | 134 | 5 | 3 | 4 | 6 | 2 | 7 |
| 6 | 1 | 69 | 3 | 2 | 8 | 5 | 7 | 4 |
| 2 | 7 | 49 | 6 | 5 | 3 | 1 | 8 | 9 |
| 5 | 4 | 159 | 7 | 9 | 1 | 2 | 6 | 3 |
| 4 | 3 | 479 | 1 | 8 | 6 | 7 | 2 | 5 |
| 9 | 2 | 19 | 4 | 7 | 5 | 6 | 3 | 8 |
| 1 | 8 | 148 | 2 | 4 | 9 | 9 | 1 | 6 |
Column 3: R1C3={1,4}, R5C3={1,9}, R7C3={4,9} → Union {1,4,9} → Eliminate 1, 4, 9 from other cells in column 3.
This 9×9 puzzle is solver-verified to require this technique on its solution path.