ExpertUsefulness: Medium
Coloring
For one candidate, colour the ends of conjugate pairs alternately and propagate. Contradictions in the colouring drive eliminations.
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Alternating colours ripple along conjugate pairs; a clash exposes a false colour.
patterneliminatesolved
How to spot it
- 1Find conjugate pairs for a digit and colour their ends opposite colours.
- 2Propagate the colours along connected pairs.
- 3Two same-colour cells in one house make that colour false; a cell seeing both colours loses the digit.
When to use
As a visual entry point to chain logic.
Common mistake
Colouring across a non-conjugate link, which breaks the logic.