Techniques › Hidden Quad › Practice
Practise the Hidden Quad
Four digits confined to four cells. The rarest subset in practical play.
8 real positions, each taken from an actual puzzle at the moment this was the cheapest move available. Two steps: find the cells that form the pattern, then find the candidate it rules out. A near miss tells you how many you had right, so getting it wrong is worth something.
| 8 | 9 | 3 | 6 | 5 | 1 | 2 | 7 | 4 |
| 2 | 6 | 7 | 4 | 3 | 9 | 5 | 1 | 8 |
| 1 | 4 | 5 | 2 | 7 | 8 | 3 | 6 | 9 |
| 37 | 12 | 8 | 9 | 46 | 5 | 47 | 23 | 1236 |
| 79 | 5 | 6 | 138 | 2 | 34 | 79 | 348 | 13 |
| 39 | 12 | 4 | 13 | 68 | 7 | 89 | 235 | 12356 |
| 5 | 8 | 9 | 7 | 1 | 234 | 6 | 234 | 23 |
| 6 | 7 | 1 | 35 | 48 | 23 | 48 | 9 | 235 |
| 4 | 3 | 2 | 58 | 9 | 6 | 1 | 58 | 7 |
How to spot it
Honestly: do not hunt for these. Find them by exhausting everything else in a stubborn house and noticing that four digits have run out of room.
Full explanation on the Hidden Quad reference page.
Practise something else
- Hidden Triple Three digits restricted to the same three cells clear everything else out of them.
- Naked Quad Four cells sharing four candidates between them. Rare, and usually preempted.