1. {A, B, C, D}
2. {A, B, C}
3. {A, B, D}
4. {A, B}
5. {A, C, D}
6. {A, C}
7. {A, D}
8. {A}
9. {B, C, D}
10. {B, C}
11. {B, D}
12. {B}
13. {C, D}
14. {C}
15. {D}
16. { }

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