Candidate skills
Pointing vs Claiming Sudoku: The Two Locked-Candidate Directions
The same box-line relationship works in two directions; naming both prevents half the pattern from disappearing from view.
Locked candidates connect a 3×3 box with a row or column. Pointing starts in the box; claiming starts in the line.
The elimination is simple once you know which unit owns the candidate and which unit receives the restriction.
Pointing: box to line
If every possible position for a digit inside a box lies on one row, that digit is locked into the row within the box. Remove it from the rest of that row outside the box.
Claiming: line to box
If every possible position for a digit in a row lies inside one box, the digit is claimed by that box. Remove it from the other cells of the box outside that row.
Use missing positions first
Write the digit’s possible cells in the starting unit and look for a single line or box. This is clearer than scanning candidate marks randomly.
Do not remove within the source set
The elimination affects peers outside the box or line. The cells that established the lock keep the candidate because they are the reason the relationship exists.
Follow the result
Locked candidates often create a single in the receiving unit. Re-scan that row, column or box before moving on to another pattern.
A small checklist
- Point from box to line
- Claim from line to box
- Map one digit at a time
- Eliminate only outside the lock
- Rescan the receiving unit
Put it into practice
Open today’s calm challenge
Use one idea from this article on a verified puzzle. There is no need to finish quickly.
Play today’s Sudoku