Locked Candidates
The umbrella term for pointing and claiming: a candidate locked to the intersection of a box and a line can be removed from the rest of whichever region it doesn't need.
Candidate 2 in this box only fits the top row — three possible cells.
How to spot it
- 1Identify a candidate confined to a box-line intersection.
- 2Decide which region it's locked within.
- 3Eliminate it from the non-intersecting cells of the other region.
When to use
As a mindset — treat every box and line intersection as a potential lock.
Common mistake
Missing locks because you check boxes but not the lines running through them.
Worked Example
Locked candidates is the umbrella term for pointing and claiming pairs — really, for any candidate trapped at the intersection of a box and a line. Whenever a candidate inside a box only fits cells along one row or column, or a line only allows a candidate inside one box, that candidate is locked.
Once you spot the lock, the direction tells you where to eliminate: clear the rest of the line if it's box → line, or the rest of the box if it's line → box. Treating every box-and-line intersection as a potential lock, rather than searching for pointing and claiming pairs separately, is what turns this from two tricks into one reliable habit.