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Box-Line Reduction (Claiming)

The inverse of a pointing pair. When a digit can only appear in the part of a row or column that intersects a single 3x3 box, the digit is locked inside that box - eliminate it from the rest of the box.

Intermediate

How to read the grids

  • Given - clues from the starting puzzle
  • Subject - cells the technique focuses on
  • Eliminated - candidates this technique removes
  • Candidate - pencil marks shown for reference

How to spot it

Sweep each row and each column for a digit. If all candidate cells for that digit fall inside a single box, the digit must be placed there. Strip it from the rest of the box.

The row claims 6 inside one box - rest of the box loses 6.

Worked example

In this row, the digit 6 can only be placed in cells that all belong to the left-center box. 6 can now be removed from every other cell of that box.

Time to practice

Reading is half the work. Try a puzzle now and look for the techniques you just learned.