Simple Colouring
Two-colour a single digit’s conjugate chain to force eliminations.
Learn Simple Colouring (single-digit chains): colour one digit’s strong links, then eliminate it where two same-colour cells clash or a cell sees both colours.
How to use it
- Build the conjugate chain. Pick a digit and find units where it has exactly two candidate cells (a strong link). Chain those links together.
- Colour the chain in two shades. Alternate two colours along every strong link. One colour is true and the other false — they cannot both be right.
- Apply the two colouring rules. If two cells of the same colour share a unit, that colour is false — clear it everywhere. Otherwise remove the digit from any cell that sees both colours.