Proven Sudoku
Techniques / Almost locked sets
ALS-XY-Wing
Also called ALS XY Wing, Triple ALS.
New to this shorthand? How to read a sudoku grid explains r4c7, houses, candidates and the rest.
What it means
Three almost full groups arranged like a wing. The middle one connects the two outer ones. Whichever way it falls, one of the outer groups is squeezed, and something gets ruled out.
The exact rule, for stronger players
The rule, stated exactly: Three almost locked sets where a hinge set shares a restricted common candidate with each of two others. A digit common to the two outer sets is eliminated from cells seeing all its positions in both.
What it removes: Remove the shared digit from cells seeing every instance in both outer sets.
Why it works: The hinge cannot supply both restricted candidates, so at least one outer set is locked, confining the shared digit inside the pair.
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
- ALS-XZTwo of those almost full groups share numbers.
Related almost-locked sets
- Death BlossomOne square is the stem.
- Subset ExclusionThe same idea for any size of group.
- Sue de CoqLook where a row or column crosses a box.
- Sue de Coq (extended)The same counting trick with more squares involved.
- Aligned Pair ExclusionLook at two squares together and list every pair of digits they could hold.
How often does it come up?
Our rough estimate: uncommon. It is the three-set case of an ALS chain.