Proven Sudoku
Techniques / Single-digit patterns
X-Coloring
Also called X-Colouring, Enhanced Coloring.
New to this shorthand? How to read a sudoku grid explains r4c7, houses, candidates and the rest.
What it means
Colouring with an extra step. As well as swapping colours, you look at squares that would be left with nowhere to put the digit. Those give you more colours to add, and more chances to find a clash.
The exact rule, for stronger players
The rule, stated exactly: Simple Coloring extended with a forcing step: if assuming a color false leads, through house-level counting, to a cell being forced, that inference is added to the coloring before applying trap and wrap.
What it removes: As for Simple Coloring, after the extra inferences are added.
Why it works: The added inference is a local forcing argument. Its soundness comes from the same one-digit-per-house rule, applied to the hypothetical.
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
- 2-String KitePick a digit.
- 3D MedusaColouring spread across every digit at once, not just one.
- 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.
How often does it come up?
Our rough estimate: rare in modern practice. Its deductions are reachable by AIC.