Proven Sudoku
Discontinuous Nice Loop
Also called Discontinuous Loop, Nice Loop (discontinuous).
New to this shorthand? How to read a sudoku grid explains r4c7, houses, candidates and the rest.
What it means
A loop that almost closes but has one weak spot. That weak spot is where the answer is. Because everything else in the loop holds, the odd one out must be true or must be false.
The exact rule, for stronger players
The rule, stated exactly: A loop where the alternation breaks at exactly one node. Two break types exist: two strong links meeting at a node, which places that candidate, and two weak links meeting at a node, which eliminates it.
What it removes: Weak-weak break eliminates the candidate at the break node. Strong-strong break places it.
Why it works: A break of two weak links means the node would have to be false to satisfy both, since assuming it true contradicts around the loop. A break of two strong links means it must be true.
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
- Continuous Nice LoopA loop where the reasoning closes back on itself with no weak spot.
Related chains
- 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.
- Forcing Chain (general form)Pick something and assume it.
- 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: more common than the continuous form, and the source of most single-elimination chain results.