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Platon Sudoku · Sudoku Study

Locked Candidates · Pointing · Step-by-step example

Within a box, every possible place for one digit lies on the same row or column. Remove that digit from the rest of the row or column outside the box.

This course is adapted from Platon Sudoku App. Read the complete example here, then continue learning and practising in the app.

View on Google Play

Recognize the pattern

Within a box, every possible place for one digit lies on the same row or column.

How to find it

Scan one digit at a time inside a box. Look for its remaining positions lining up on one row or column.

What it allows

Remove that digit from the rest of the row or column outside the box.

Avoid the mix-up

The digit need not be fixed to one cell. Every possible place inside the box must share the line. Claiming starts from a row or column and removes candidates elsewhere in a box.

Step-by-step example · Row

This example starts from a saved intermediate position. Its candidates include earlier logical eliminations; they are not fresh automatic notes.

Blue: evidence. Green: conclusion. Crossed-out digits: eliminated candidates. R1C1 means row 1, column 1.

Step 1 · Where to look

In box 5, 6 can go only in R5C4, R5C6. The digit must appear once in this region.

In box 5, 6 can go only in R5C4, R5C6. The digit must appear once in this region.
In box 5, 6 can go only in R5C4, R5C6. The digit must appear once in this region.
Step 2 · Lock the digit into the intersection

All positions in box 5 lie in row 5. Since box 5 must contain 6, the intersection supplies it. Other cells in row 5 cannot contain 6.

All positions in box 5 lie in row 5. Since box 5 must contain 6, the intersection supplies it. Other cells in row 5 cannot contain 6.
All positions in box 5 lie in row 5. Since box 5 must contain 6, the intersection supplies it. Other cells in row 5 cannot contain 6.
Step 3 · Conclusion

The 6 in box 5 must lie in row 5. Therefore the targets in row 5 but outside box 5 cannot be 6: R5C1=6, R5C2=6.

The 6 in box 5 must lie in row 5. Therefore the targets in row 5 but outside box 5 cannot be 6: R5C1=6, R5C2=6.
The 6 in box 5 must lie in row 5. Therefore the targets in row 5 but outside box 5 cannot be 6: R5C1=6, R5C2=6.

What it allows

The 6 in box 5 must lie in row 5. Therefore the targets in row 5 but outside box 5 cannot be 6: R5C1=6, R5C2=6.

Locked Candidates · Pointing · Remove that digit from the rest of the row or column outside the box.
Locked Candidates · Pointing · Remove that digit from the rest of the row or column outside the box.

Step-by-step example · Column

This example starts from a saved intermediate position. Its candidates include earlier logical eliminations; they are not fresh automatic notes.

Blue: evidence. Green: conclusion. Crossed-out digits: eliminated candidates. R1C1 means row 1, column 1.

Step 1 · Where to look

In box 4, 4 can go only in R4C3, R6C3. The digit must appear once in this region.

In box 4, 4 can go only in R4C3, R6C3. The digit must appear once in this region.
In box 4, 4 can go only in R4C3, R6C3. The digit must appear once in this region.
Step 2 · Lock the digit into the intersection

All positions in box 4 lie in column 3. Since box 4 must contain 4, the intersection supplies it. Other cells in column 3 cannot contain 4.

All positions in box 4 lie in column 3. Since box 4 must contain 4, the intersection supplies it. Other cells in column 3 cannot contain 4.
All positions in box 4 lie in column 3. Since box 4 must contain 4, the intersection supplies it. Other cells in column 3 cannot contain 4.
Step 3 · Conclusion

The 4 in box 4 must lie in column 3. Therefore the targets in column 3 but outside box 4 cannot be 4: R1C3=4, R2C3=4.

The 4 in box 4 must lie in column 3. Therefore the targets in column 3 but outside box 4 cannot be 4: R1C3=4, R2C3=4.
The 4 in box 4 must lie in column 3. Therefore the targets in column 3 but outside box 4 cannot be 4: R1C3=4, R2C3=4.

What it allows

The 4 in box 4 must lie in column 3. Therefore the targets in column 3 but outside box 4 cannot be 4: R1C3=4, R2C3=4.

Locked Candidates · Pointing · Remove that digit from the rest of the row or column outside the box.
Locked Candidates · Pointing · Remove that digit from the rest of the row or column outside the box.

Practice

This course is adapted from Platon Sudoku App. Read the complete example here, then continue learning and practising in the app.

View on Google Play