Proven Sudoku
Digit Forcing Chain
Also called Digit Forcing Chains.
New to this shorthand? How to read a sudoku grid explains r4c7, houses, candidates and the rest.
What it means
Take one number in one square. Try it being true, then try it being false. If both roads reach the same place, that place is true.
The exact rule, for stronger players
The rule, stated exactly: Take a single candidate true and false as the two branches. If both force the same conclusion, it holds.
What it removes: Apply the common conclusion.
Why it works: A candidate is either true or false, so the two branches are exhaustive.
Worked examples
None yet. This pattern does not turn up in our daily boards, so there is no real example to show. We would rather wait than draw a fake one.
Learn these first
- Forcing Chain (general form)Pick something and assume it.
Related chains
- Discontinuous Nice LoopA loop that almost closes but has one weak spot.
- Dynamic Forcing Chain with ContradictionAssume a digit is right.
- Dynamic Forcing Chain with Double ImplicationTry both options for a square and follow each one out fully.
- Grouped AICA chain where a step can use a whole group of squares at once instead of a single square.
- KrakenTake a pattern that nearly works.
How often does it come up?
Our rough estimate: common. The two-branch form is the cheapest forcing split.