Contradiction
Extreme
Used by Smart Hint
Placing this digit here forces some run into an impossible position — so it can be ruled out.
- Cells that establish the pattern
- Where the conclusion lands
- Digit ruled out
How it works
- The same run as Agreement, one step earlier: three cells making 17, with the middle capped to {8, 9} and the last to {7, 9} by their down runs.
- Suppose the first cell were 3. The other two would have to make 17 − 3 = 14.
- The smallest they can manage together is 8 + 7 = 15. There's no way to finish the run.
- The supposition breaks the board, so it was wrong: strike 3. This is the last resort — reach for it only once every other rung is exhausted, because it costs a full trial per candidate.