LG-009

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

We must include blue and exclude red.

If we include green, we must exclude purple.

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

• 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).