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INTERMEDIATE TECHNIQUE

Box-Line Reduction

If a row can only place a digit inside one box, the rest of that box cannot have it.

What is box-line reduction?

Box-line reduction, also called claiming, is the reverse of a pointing pair. Look at a row or a column: if every candidate for a digit in that line falls inside the same box, the line "claims" the digit for that box. The digit must be in the line's cells inside the box, so it can be removed from the box's other cells.

In row 4, 7 can only go in columns 1 or 3, both inside the middle-left box. So 7 cannot be anywhere else in that box: it is removed from rows 5 and 6.

How to use it

  1. Pick a row or column and a digit missing from it.
  2. Find its candidates along the line.
  3. Check if they share a box. If all of them fall inside the same 3×3 box, you have a claim.
  4. Eliminate the digit from the other cells of that box (those not on the line).

When a row has only two or three empty cells left, check it for claims first: the remaining digits are often confined to a single box.

Practice box-line reductionTry the technique on a fresh Hard puzzle.
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GOOD TO KNOW

A little clarity
before you play.

The details, without the distractions.

Is claiming the same as box-line reduction?

Yes. Both names describe the same technique.

When is box-line reduction useful?

Mostly on Hard and Expert puzzles, after the easy singles are gone and candidate notes are filled in.

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