Proven Sudoku
Techniques / Almost locked sets
Almost Locked Candidates
Also called ALC, Almost Locked Candidate.
New to this shorthand? How to read a sudoku grid explains r4c7, houses, candidates and the rest.
What it means
Two areas cross. Between them they nearly trap a set of numbers. Just one spare spot stops it. Check that one spot and you learn what has to go.
The exact rule, for stronger players
The rule, stated exactly: A locked candidates pattern that fails by one cell. Combined with a chain or a second almost pattern, it yields eliminations.
What it removes: Depends on the combining structure.
Why it works: The locked candidates argument holds unless the escaping cell takes the digit, so the conclusion holds conditionally on that cell, which is a chain node.
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
- Locked Candidates (general form)Sometimes all the spots for a digit inside one group also sit inside a second group.
- Almost Locked SetA small group of squares holding exactly one number more than there are squares.
Related almost-locked sets
- ALS ChainA row of almost full groups linked one to the next.
- ALS-XY-WingThree almost full groups arranged like a wing.
- ALS-XZTwo of those almost full groups share numbers.
- Death BlossomOne square is the stem.
- Subset ExclusionThe same idea for any size of group.
How often does it come up?
Our rough estimate: uncommon as a named pattern.