Proven Sudoku
Techniques / Single-digit patterns
3D Medusa
Also called Medusa, 3D Colouring, Multi-digit coloring.
New to this shorthand? How to read a sudoku grid explains r4c7, houses, candidates and the rest.
What it means
Colouring spread across every digit at once, not just one. You mark squares and digits that must go together, then look for two marks of the same colour that clash. When they do, that whole colour is wrong.
The exact rule, for stronger players
The rule, stated exactly: Extend coloring across digits. Vertices are candidates (cell, digit) pairs; edges are strong links, either two cells conjugate on a digit or two digits in a bivalue cell. Two-color the component and apply the coloring rules across the whole structure.
What it removes: Remove candidates seeing both colors; if a color contradicts, the other color is placed wholesale.
Why it works: Bivalue cells provide strong links between different digits in the same cell, so the alternation extends into a three-dimensional structure. Exactly one color is true, and the same trap and wrap arguments apply.
Worked examples
None yet. This pattern does not turn up in our daily boards, so there is no real example to show. We would rather wait than draw a fake one.
Learn these first
- Simple ColoringPick a digit.
Related single-digit patterns
- Empty RectangleIn one box, all the homes for a digit sit in one row and one column.
- Multi-ColoringColouring marks a digit's spots in two shades.
- SkyscraperPick a digit.
- Turbot FishPick one digit.
- X-ColoringColouring with an extra step.
How often does it come up?
Our rough estimate: uncommon but powerful when it appears, often resolving a large part of the grid at once.