Locked Candidates Type 2 (Claiming)
intermediateWhen candidates in a line are locked to one box
Claiming occurs when all instances of a candidate in a row or column are within the same box.
Understanding the Concept
Also called "Line/Box Reduction" or "Box Claiming".
If a candidate appears only in one box within a row (or column), it must be placed in that box.
Therefore, the candidate can be eliminated from other cells in that box not on that line.
This is the reverse of pointing pairs - here the line claims the candidates for one box.
The digit must appear in the row/column, and it's constrained to one box.
Like pointing pairs, this can involve 2 or 3 candidates.
Examples
Claiming Pair in Row 2
In row 2, candidate 9 only appears in box 1 (at R2C3 and R2C4). Since 9 must be somewhere in row 2 and it can only go in box 1, we eliminate 9 from all other cells in box 1 that are not in row 2.
Pro Tips
- •Check each candidate in each row and column
- •Look for candidates confined to a single box within the line
- •The elimination happens within the box, off the line
- •Often found together with pointing pairs
