Sudoku with an extra layer of clues. Between some neighbouring squares are dots: a white dot means the two numbers are consecutive (like 4 and 5), and a black dot means one is double the other (like 3 and 6). Every dot is shown — so where there is no dot, the two numbers are neither.
The dots let you place numbers with very few givens. A black dot can only join pairs like 1–2, 2–4, 3–6 and 4–8, so a square next to a black dot can never be 5, 7 or 9. A 1 next to a white dot must have a 2 beside it.
Once you get the feel of the dots, even an almost empty grid gives way to logic.
A sudoku where white dots join consecutive numbers, black dots join a number and its double, and no dot means neither.
The full guide, with a worked example and common mistakes: How to play Dot Sudoku.
They are consecutive and double, so either a white or a black dot may join them.
Yes — so two neighbours without a dot are neither consecutive nor double.
Yes — every puzzle is checked so that logic reaches the unique answer.