Answer
2. If a bird is in this aviary, then it belongs to me.
4. If a bird belongs to me, then it is at least 9 feet high.
1. If a bird is at least 9 feet high, then it is an ostrich.
3. If a bird lives on mince pies, then it is not an ostrich.
Contrapositive: If a bird is an ostrich, then it does not live on mince pies.
∴ If a bird is in this aviary, then it does not live on mince pies; that is, no bird in this aviary lives on mince pies.
Work Step by Step
Universal transitivity:
∀x,P(x)→Q(x).
∀x,Q(x)→R(x).
∴∀x,P(x)→R(x).
