The case notes
Count matching digits in the corners and centre ring
There is a surprising match on a nine-by-nine Sudoku. The four corner blocks and the ring around the centre hold the same collection of digits. Watch a worked example, then try the idea in a puzzle.
Put it into practice
Corners ↔ centre ring
There is a surprising match on a nine-by-nine Sudoku. The four corner blocks and the ring around the centre hold the same collection of digits.
Eight groups on each side
Why do they match? Count the two outer rows and columns on each side, then count the eight outer boxes. Each count uses eight complete Sudoku groups. The cells they share cancel, leaving the corners balanced against the ring.
Corners contain one 3
Look only at threes. One three is given in a corner. The other corner cells all see a three already, so the corners contain exactly one.
Only r3c6 can hold 3
The ring must therefore contain one three as well. Existing threes block every ring cell but this one: row three, column six.
r3c6 = 3
Place three there. Matching digit counts turned a distant corner clue into a move beside the centre.
Read the transcript
There is a surprising match on a nine-by-nine Sudoku. The four corner blocks and the ring around the centre hold the same collection of digits. Why do they match? Count the two outer rows and columns on each side, then count the eight outer boxes. Each count uses eight complete Sudoku groups. The cells they share cancel, leaving the corners balanced against the ring. Look only at threes. One three is given in a corner. The other corner cells all see a three already, so the corners contain exactly one. The ring must therefore contain one three as well. Existing threes block every ring cell but this one: row three, column six. Place three there. Matching digit counts turned a distant corner clue into a move beside the centre.
