Proven Sudoku
Dynamic Forcing Chain with Contradiction
Also called Dynamic Contradiction Chain, Contradiction Forcing Chain.
New to this shorthand? How to read a sudoku grid explains r4c7, houses, candidates and the rest.
What it means
Assume a digit is right. Follow what that forces. Then follow what those results force, and keep going. If you end up somewhere impossible, your first guess was wrong.
The exact rule, for stronger players
The rule, stated exactly: Assume a candidate true, propagate using every available simple technique on the modified grid, and derive a contradiction. The candidate is then false.
What it removes: Eliminate the assumed candidate.
Why it works: Reductio. If the assumption produces an impossible grid state, the assumption was wrong.
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
- 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.
- NishioAssume a number goes in a square, then check whether the rest of that number can still fit everywhere it needs to.
- Nishio Forcing NetThe same check as Nishio.
How often does it come up?
Our rough estimate: this is where logical solving shades into guided trial and error, and the page should be honest that many solvers do not accept it as a solving technique.