LG-006

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

We must include green and exclude yellow.

If we include blue, we must exclude red.

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

• 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).