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Platon Sudoku · Sudoku Study

Locked candidates · Core Concepts

Pointing starts with all positions in a box on one line and removes that digit on the line outside the box. Claiming starts with all positions on a line inside one box and removes the digit elsewhere in that 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

Definition

Pointing starts with all positions in a box on one line and removes that digit on the line outside the box. Claiming starts with all positions on a line inside one box and removes the digit elsewhere in that box.

How to find it

Choose the source box or line, count every position for the digit, then check whether they all lie in its intersection with the other region.

Common mistake

A source position outside that intersection prevents the claimed elimination.

Pointing · Row

Teaching board · local candidate diagram

Observe candidates

Pointing starts with all positions in a box on one line and removes that digit on the line outside the box. Claiming starts with all positions on a line inside one box and removes the digit elsewhere in that box.

All 2s in box 1 lie in its intersection with row 2; 2 at r2c6 can be excluded.
All 2s in box 1 lie in its intersection with row 2; 2 at r2c6 can be excluded.
Verify the condition

Choose the source box or line, count every position for the digit, then check whether they all lie in its intersection with the other region.

All 2s in box 1 lie in its intersection with row 2; 2 at r2c6 can be excluded.
All 2s in box 1 lie in its intersection with row 2; 2 at r2c6 can be excluded.
Draw the conclusion

All source candidates lie in the box-line intersection, so the target in the other part of the affected region can be removed.

All 2s in box 1 lie in its intersection with row 2; 2 at r2c6 can be excluded.
All 2s in box 1 lie in its intersection with row 2; 2 at r2c6 can be excluded.

Pointing · Column

Teaching board · local candidate diagram

Observe candidates

Pointing starts with all positions in a box on one line and removes that digit on the line outside the box. Claiming starts with all positions on a line inside one box and removes the digit elsewhere in that box.

All 2s in box 1 lie in its intersection with column 2; 2 at r6c2 can be excluded.
All 2s in box 1 lie in its intersection with column 2; 2 at r6c2 can be excluded.
Verify the condition

Choose the source box or line, count every position for the digit, then check whether they all lie in its intersection with the other region.

All 2s in box 1 lie in its intersection with column 2; 2 at r6c2 can be excluded.
All 2s in box 1 lie in its intersection with column 2; 2 at r6c2 can be excluded.
Draw the conclusion

All source candidates lie in the box-line intersection, so the target in the other part of the affected region can be removed.

All 2s in box 1 lie in its intersection with column 2; 2 at r6c2 can be excluded.
All 2s in box 1 lie in its intersection with column 2; 2 at r6c2 can be excluded.

Claiming · Row

Teaching board · local candidate diagram

Observe candidates

Pointing starts with all positions in a box on one line and removes that digit on the line outside the box. Claiming starts with all positions on a line inside one box and removes the digit elsewhere in that box.

All 2s in row 2 lie in its intersection with box 1; 2 at r1c3 can be excluded.
All 2s in row 2 lie in its intersection with box 1; 2 at r1c3 can be excluded.
Verify the condition

Choose the source box or line, count every position for the digit, then check whether they all lie in its intersection with the other region.

All 2s in row 2 lie in its intersection with box 1; 2 at r1c3 can be excluded.
All 2s in row 2 lie in its intersection with box 1; 2 at r1c3 can be excluded.
Draw the conclusion

All source candidates lie in the box-line intersection, so the target in the other part of the affected region can be removed.

All 2s in row 2 lie in its intersection with box 1; 2 at r1c3 can be excluded.
All 2s in row 2 lie in its intersection with box 1; 2 at r1c3 can be excluded.

Claiming · Column

Teaching board · local candidate diagram

Observe candidates

Pointing starts with all positions in a box on one line and removes that digit on the line outside the box. Claiming starts with all positions on a line inside one box and removes the digit elsewhere in that box.

All 2s in column 2 lie in its intersection with box 1; 2 at r3c1 can be excluded.
All 2s in column 2 lie in its intersection with box 1; 2 at r3c1 can be excluded.
Verify the condition

Choose the source box or line, count every position for the digit, then check whether they all lie in its intersection with the other region.

All 2s in column 2 lie in its intersection with box 1; 2 at r3c1 can be excluded.
All 2s in column 2 lie in its intersection with box 1; 2 at r3c1 can be excluded.
Draw the conclusion

All source candidates lie in the box-line intersection, so the target in the other part of the affected region can be removed.

All 2s in column 2 lie in its intersection with box 1; 2 at r3c1 can be excluded.
All 2s in column 2 lie in its intersection with box 1; 2 at r3c1 can be excluded.

Recognition practice

Teaching board · local candidate diagram

Recognition practice 1

Do the marked candidates satisfy this locked-candidate relation?

Teaching board · local candidate diagram
Teaching board · local candidate diagram
Draw the conclusion

Yes

Recognition practice 2

Do the marked candidates satisfy this locked-candidate relation?

Teaching board · local candidate diagram
Teaching board · local candidate diagram
Draw the conclusion

No

Recognition practice 3

Do the marked candidates satisfy this locked-candidate relation?

Teaching board · local candidate diagram
Teaching board · local candidate diagram
Draw the conclusion

Yes

Recognition practice 4

Do the marked candidates satisfy this locked-candidate relation?

Teaching board · local candidate diagram
Teaching board · local candidate diagram
Draw the conclusion

No

Recognition practice 5

Do the marked candidates satisfy this locked-candidate relation?

Teaching board · local candidate diagram
Teaching board · local candidate diagram
Draw the conclusion

Yes

Recognition practice 6

Do the marked candidates satisfy this locked-candidate relation?

Teaching board · local candidate diagram
Teaching board · local candidate diagram
Draw the conclusion

No

Recognition practice 7

Do the marked candidates satisfy this locked-candidate relation?

Teaching board · local candidate diagram
Teaching board · local candidate diagram
Draw the conclusion

Yes

Recognition practice 8

Do the marked candidates satisfy this locked-candidate relation?

Teaching board · local candidate diagram
Teaching board · local candidate diagram
Draw the conclusion

No

Recognition practice 9

Do the marked candidates satisfy this locked-candidate relation?

Teaching board · local candidate diagram
Teaching board · local candidate diagram
Draw the conclusion

Yes

Recognition practice 10

Do the marked candidates satisfy this locked-candidate relation?

Teaching board · local candidate diagram
Teaching board · local candidate diagram
Draw the conclusion

No

Recognition practice 11

Do the marked candidates satisfy this locked-candidate relation?

Teaching board · local candidate diagram
Teaching board · local candidate diagram
Draw the conclusion

Yes

Recognition practice 12

Do the marked candidates satisfy this locked-candidate relation?

Teaching board · local candidate diagram
Teaching board · local candidate diagram
Draw the conclusion

No

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