[Q14] PQ-Trees: Introduction

With respect of what set a pruned pertinent subtree can be formed from the tree below, and satisfies the definition of a proper PQ-Tree?

1. {0, 1, 2, 5, 6}
2. {7, 8, 9, 10}
3. {1, 2, 3, 4, 5, 6}
4. {7, 8, 10, 11}
5. None of the above.

Original idea by: Juan Felipe Hernández Albarracín.