Armstrong's inference rules
Armstrong's rules (provable directly from the definitions):
- IR1. Reflexive rule: if X?Y, then X?Y
- IR2. Augmentation rule: if X?Y then XZ?YZ
- IR3. Transitive rule: if X?Y and Y?Z then X?Z
If you understand the idea of FD, these should make sense, even if you can't prove them formally.