Locked Candidates

A solving technique that uses the intersections between lines and boxes.

Aliases include: Intersection Removal, Line-Box Interaction. The terms Pointing and Claiming / Box-Line Reduction are often used to distinguish the 2 types.

This is a basic solving technique. When all candidates for a digit in a house are located inside the intersection with another house, we can eliminate the remaining candidates from the second house outside the intersection.

Type 1 (Pointing)

All the candidates for digit X in a box are confined to a single line (row or column). The surplus candidates are eliminated from the part of the line that does not intersect with this box.

Locked Candidates , How to solve sudoku puzzles - Solving sudoku strategy

Legend:
X : cell which may contain a candidate for digit X
- : cell which does not contain a candidate for digit X
* : cell from which we may eliminate the candidates for digit X

Depending on the number of available candidates in the intersection, this technique is also known as a Pointing Pair or Pointing Triple.

Type 2 (Claiming or Box-Line Reduction)

All the candidates for digit X in a line are confined to a single box. The surplus candidates are eliminated from the part of the box that does not intersect with this line.

Locked Candidates , Sudoku solving technique

Example

Locked Candidates, Sudoku solving technique

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