Kropki Sudoku rules and puzzles

The case notes

Use a black dot to protect a box’s last one

This black dot sits inside the top-left box. Let’s use the box to test a candidate on the dot. Watch a worked example, then try the idea in a puzzle.

Put it into practice

A dot inside a Sudoku box

This black dot sits inside the top-left box. Let’s use the box to test a candidate on the dot.

The box’s 1 is on the dotted pair

The box needs a one. These ones in rows two and three exclude it from both lower rows here, while three occupies the other top-row cell. So one must be on the dotted pair.

Try 4 → partner 2 or 8

Try four in the left dot cell. A black dot doubles or halves it, so the partner would be two or eight. Neither cell could hold the box’s one.

Remove 4 from r1c1

That would leave the box without one. Four is impossible in the left dot cell. The dot has pointed beyond its pair to the whole box.

Read the transcript

This black dot sits inside the top-left box. Let’s use the box to test a candidate on the dot. The box needs a one. These ones in rows two and three exclude it from both lower rows here, while three occupies the other top-row cell. So one must be on the dotted pair. Try four in the left dot cell. A black dot doubles or halves it, so the partner would be two or eight. Neither cell could hold the box’s one. That would leave the box without one. Four is impossible in the left dot cell. The dot has pointed beyond its pair to the whole box.

Keep following the clues