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 chain of 7s through row 1, column 5, and row 4.
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, R1C5, R4C5, and R4C2 alternate gold and blue through three strong links.
Step 3 of 4
Find a cell that sees both colors
R5C1 sees the gold 7 at R1C1 in column 1 and the blue 7 at R4C2 in box 4, so it cannot contain 7 under either coloring.
Step 4 of 4
Keep the colors, remove the trap
The chain remains unresolved while R5C1 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