Simple Coloring
Advanced Logic27 / 32Paint a digit's strong links in two colors and watch one fail.
Wherever a unit holds a digit in exactly two cells, those cells form a strong link: exactly one of them is true. Chain the links together and alternate two colors — all cells of one color are true together, and the other color entirely false.
Two ways to profit: if one color appears twice in a unit, that whole color is false. And any uncolored candidate that sees both colors is false no matter which color wins.
See it in action
Step 1 of 4
The setup
Pick a digit rich in strong links (units with exactly two candidates). Color one cell, propagate along the links, and inspect: same color twice in a unit? Uncolored cells seeing both colors? Step through this real position to see it happen.
Practice
Color the strong-link chain and remove the digit from every candidate the coloring convicts.
Drill 1 of 29Tap a cell, then the candidate digit you want to remove.