Forcing Chain Variants (Digit, Cell, Unit, Quad)
Extreme
Reference only
Named by what's exhaustively tested — every candidate of one digit, every candidate of one cell, every cell of one unit, or every cell across four related units — each variant follows every branch to see if they all agree on some outcome.
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
- Where the conclusion lands
- Candidate ruled out
How it works
- A Cell Forcing Chain tests every candidate of one cell (say A1's {2, 6}) and follows each one's consequences forward independently.
- If both branches — A1=2 and A1=6 — end up agreeing that E5 can't be 8, that elimination holds regardless of which branch is actually true. Digit/Unit/Quad Forcing Chains apply the identical exhaustive-branch idea, just starting from a digit's every occurrence, a unit's every cell, or four related units at once instead of one cell's candidates.