Give reasons for the steps, given premises 1, 2 and 3:
1. X ⊃ (Y ⊃ Z)
2. X ⊃ (A ⊃ B)
3. X • (Y ∨ A) /∴ ∼B ⊃ X
4. X 3, Simplification
5. A ⊃ B 2,4, Modus Ponens
6. Y ⊃ Z 1,4, Modus Ponens
7. (Y ∨ A) • X 3, Commutation
8. Y ∨ A 7, Simplification
9. ∼(∼Y) ∨ A 8, Double Negation
10. ∼Y ⊃ A 10, Material Implication
11. ∼Y ⊃ B 10,5, Hypothetical Syllogism
12. ∼B ⊃ ∼(∼Y) 11, Transposition
13. ∼B ⊃ Y 12, Double Negation
14. X ∨ ∼Y 4, Addition
15. ∼Y ∨ X 14, Commutation
16. Y ⊃ X 15, Material Implication
17. ∼B ⊃ X 13,16, Hypothetical syllogism
Edwin