✓ SET: shape and fill are the same on all, color and count all differ
✗ Not a SET: color matches on only two cards (two red, one purple)
Each of the 4 features (shape, color, fill, count) must be either the same on all three cards or different on all three.
How to hunt for a SET
1. Pick any two cards — they always start a SET. Work out which third card completes them (same features → the same, different → the third option) and look for it.
2. If any feature matches on exactly two of the three cards — it is never a SET.
3. Start with what is rare: few squares or striped cards on the board — test triples with them first.