1. (O ⊃ C) • (∼S ⊃ ∼D) 2. (E ⊃ D) • (∼E ⊃ ∼C) / O ⊃ S 3. O ⊃ C 1, Simplification 4. (∼E ⊃ ∼C) • (E ⊃ D) 2, Commutation 5. ∼E ⊃ ∼C 4, Simplification 6. ∼∼C ⊃ ∼∼E 5, Transposition 7. C ⊃ E 6, Double Negation 8. O ⊃ E 3,7, Hypothetical Syllogism 9. E ⊃ D 2, Simplification 10. O ⊃ D 8,9, Hypothetical Syllogism 11. (∼S ⊃ ∼D) • (O ⊃ C) 1, Commutation 12. ∼S ⊃ ∼D 11, Simplification 13. ∼∼D ⊃ ∼∼S 12, Transposition 14. D ⊃ S 13, Double Negation 15. O ⊃ S 10,14, Hypothetical Syllogism Edwin