The case notes
How disjoint groups work
Cells in the same position inside each three-by-three box hold different digits. Watch a worked example, then try the idea in a puzzle.
Put it into practice
Same spot in every box
Disjoint groups add nine hidden groups to an ordinary Sudoku. Start with the upper-left cell of each box.
Nine cells, no repeats
These nine matching positions must contain different digits. They work like another row or box, even though they are spread out.
No 5 in this matching spot
There is a five in the first of them. The matching cell in the centre box cannot be five.
One group per box position
Those two cells share no row, column or box. Their matching position is the new link. Every other position gets its own group.
Read the transcript
Disjoint groups add nine hidden groups to an ordinary Sudoku. Start with the upper-left cell of each box. These nine matching positions must contain different digits. They work like another row or box, even though they are spread out. There is a five in the first of them. The matching cell in the centre box cannot be five. Those two cells share no row, column or box. Their matching position is the new link. Every other position gets its own group.
