LG-005

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

We must include red and exclude yellow.

If we include green, we must exclude blue.

The only option that satisfies all constraints is: red, green, 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).