Platon Sudoku · Sudoku Study
Locked Pair · Step-by-step example
Two cells in the intersection of a row and box, or column and box, each contain only the same two candidates. Remove both digits from all other cells in both shared regions.
This course is adapted from Platon Sudoku App. Read the complete example here, then continue learning and practising in the app.
View on Google PlayRecognize the pattern
Two cells in the intersection of a row and box, or column and box, each contain only the same two candidates.
How to find it
Find a naked pair, then check whether both cells also share a box as well as their row or column.
What it allows
Remove both digits from all other cells in both shared regions.
Avoid the mix-up
A pair sharing only one region is a naked pair. Both cells must have exactly the two candidates; an extra candidate breaks the lock.
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 · Find the pair
The two highlighted cells contain only 1 and 7. They form a pair: one must be 1, the other 7.
Step 2 · See the shared regions
The pair lies in both row 1 and box 1. These two cells reserve 1 and 7, so no other cell in either region can use them.
Step 3 · Remove the targets
Remove the marked 1, 7 candidates from the other cells in row 1 and box 1.
What it allows
Remove the marked 1, 7 candidates from the other cells in row 1 and box 1.
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 · Find the pair
The two highlighted cells contain only 5 and 8. They form a pair: one must be 5, the other 8.
Step 2 · See the shared regions
The pair lies in both column 8 and box 6. These two cells reserve 5 and 8, so no other cell in either region can use them.
Step 3 · Remove the targets
Remove the marked 5, 8 candidates from the other cells in column 8 and box 6.
What it allows
Remove the marked 5, 8 candidates from the other cells in column 8 and box 6.
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