Forcing Chains
Extreme
Reference only
Follows the consequences of both options in a bivalue cell until they force the same outcome somewhere else on the board.
The solver does not attempt this technique, so Smart Hint will never suggest it. It is documented because you may still want to spot it yourself.
- First colour in the chain
- Second colour in the chain
- Cells that establish the pattern
- Where the conclusion lands
- Candidate ruled out
How it works
- A1 has only two candidates, 3 and 7 — so the whole puzzle splits into exactly two possible worlds.
- Follow the chain if A1 is 3: it forces E1 to be 3, which (through further links not all shown here) rules out 9 at E5.
- Follow the chain if A1 is 7 instead: it forces A5 to be 7, which also ends up ruling out 9 at E5. Since both worlds agree, 9 can be eliminated from E5 regardless of which is true.