LG-013

Constraint puzzle: A code uses 3 colors. You know:
1) yellow is used.
2) If blue is used, then purple is not used.
3) green is not used.
Which set of colors is possible?

We must include yellow and exclude green.

If we include blue, we must exclude purple.

The only option that satisfies all constraints is: yellow, blue, red.

• Picking the first pattern you see without checking it against all rows/columns.
• Ignoring the simplest rule (counts, rotations, alternations) and jumping to a complex story.
• Not testing your rule on the middle row/column (where many puzzles “break” bad rules).