Trial and Error
Extreme
Used by Smart Hint
When no other technique applies, suppose a candidate and follow it through — if that leads to an impossible board, the candidate is ruled out for good.
- Second colour in the chain
- Where the conclusion lands
How it works
- A1 has two candidates, 4 and 7, and no other technique can decide between them.
- Suppose 4 and push the easy consequences through. If that ends with some cell holding zero legal candidates — like D1 here — then 4 was impossible.
- So strike 4 from A1 and carry on. This is a real deduction, not a guess you keep: the refuted digit is gone for good, and only the surviving candidate had to be true. It stays the last resort — every technique above exists to avoid needing it.