Simple coloring: alternate one digit through strong links
Simple coloring follows one digit through units where it has exactly two positions, assigning alternating colors to each conjugate pair.
Key idea
One color is true and the other false throughout the chain. An uncolored candidate that sees both colors can never be true.
See the move, step by step
Color a short chain of 7s inside the top-left of the grid.
Step 1 of 4
Choose one digit and one component
Start from a conjugate pair for candidate 7 and extend only through connected strong links.
Step 2 of 4
Alternate the two colors
The 7s at R1C1, R1C2, R2C2, and R2C3 alternate gold and blue through three strong links.
Step 3 of 4
Find a cell that sees both colors
R3C1 sees a gold 7 and a blue 7 in box 1, so it cannot be true under either coloring.
Step 4 of 4
Keep the colors, remove the trap
The chain remains unresolved while R3C1 loses candidate 7.
Try it on today's puzzle
Build one connected coloring component at a time. Never merge unrelated conjugate-pair networks under the same two colors.
Play today