Box/Line Reduction in Sudoku (Claiming)
This is the pointing pair turned around. There, a box decided something about a row. Here a row or column decides something about a box. Cells are named by row and column: r1c5 is row 1, column 5.
Step 1 of 4
The row claims the box
Row 1 still needs an 8, and only two of its cells can take it: the ringed cells, r1c5 and r1c6. Both are in box 2, the top-middle box. So row 1's 8 is box 2's 8 as well, and no other cell of box 2 can hold an 8.
This is box/line reduction, also called claiming: when a row's or column's candidates for a digit all fall in one box, clear that digit from the rest of the box. Here r2c5 and r3c6 lose their 8s.
Use the claim
Two cells of box 2 lose an 8. Look at what each one has left: one of them is down to a single candidate.
Your move
Clear the 8 from box 2 outside row 1, then place the digit it unlocks.
Which cells lose the 8?
Row 1's 8 is in r1c5 or r1c6, both in box 2. Which cells lose their 8?
Find the claim
Every empty cell has its candidates pencilled in, and none has just one. Look line by line for a digit whose candidates all fall in one box.
Your move
Find the claim that unlocks a digit, then place it.
What you learned
- If a row's or column's candidates for a digit all fall in one box, the box's digit is on that line.
- Clear the digit from the rest of the box, off the line.
- Pointing and claiming are the same overlap read both ways: box to line, and line to box.
In this course
Unit 1The rules
Unit 2Solving techniques
Take it to the table.
Put what you just read into practice. No sign-up needed.