The case notes
How the anti-knight rule works
Cells a chess knight's move apart cannot hold the same digit. Watch a worked example, then try the idea in a puzzle.
Put it into practice
The knight cannot repeat
In an anti-knight Sudoku, equal digits cannot sit a chess knight move apart. Here is a five at the centre.
Two away, one across
A knight travels two cells one way, then one across. This cell up and left is one such destination.
No 5 here
This cell shares no row, column or box with the five. Ordinary Sudoku allows five here, but anti-knight rules it out.
Eight affected cells
The same applies to all eight knight destinations around this five. Each of these cells loses five as a possibility.
One extra rule to check
Keep the normal Sudoku rules. Add one more check: equal digits cannot be a knight move apart.
Read the transcript
In an anti-knight Sudoku, equal digits cannot sit a chess knight move apart. Here is a five at the centre. A knight travels two cells one way, then one across. This cell up and left is one such destination. This cell shares no row, column or box with the five. Ordinary Sudoku allows five here, but anti-knight rules it out. The same applies to all eight knight destinations around this five. Each of these cells loses five as a possibility. Keep the normal Sudoku rules. Add one more check: equal digits cannot be a knight move apart.
