Proven Sudoku
AIC with ALS Nodes
Also called ALS-AIC, AIC with almost locked sets.
New to this shorthand? How to read a sudoku grid explains r4c7, houses, candidates and the rest.
What it means
A chain that can step through a small set of squares holding one more number than it has room for. Those sets act like a single link. It makes chains much more powerful.
The exact rule, for stronger players
The rule, stated exactly: An AIC in which a node is an almost locked set, entered on one digit and exited on another. Entering means the entry digit is false in the ALS, which locks it.
What it removes: As for AIC.
Why it works: An ALS with one digit removed becomes a locked set, forcing its remaining digits. That gives a strong inference from the entry digit being false to any other digit being confined inside the set.
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
- Alternating Inference ChainA chain that switches between two kinds of step.
- Almost Locked SetA small group of squares holding exactly one number more than there are squares.
Related chains
- Bowman's BingoPick a digit, assume it, and write out everything that follows until you either finish or hit a contradiction.
- Cell Forcing ChainTake one square and try each number it could hold.
- Continuous Nice LoopA loop where the reasoning closes back on itself with no weak spot.
- Digit Forcing ChainTake one number in one square.
- Discontinuous Nice LoopA loop that almost closes but has one weak spot.
How often does it come up?
Our rough estimate: common in hard solving, and it subsumes ALS-XZ and ALS chains.