LG-011

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

We must include green and exclude red.

If we include yellow, we must exclude purple.

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

• 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).