1. (O ⊃ C ) ● (∼S ⊃ ∼D) 2. (E ⊃ D) ● (∼E ⊃ ∼C ) / O ⊃ S 3. O ⊃ C 1, Simplification 4. (∼S ⊃ ∼D) ● (O ⊃ C ) 1, Commutation 5. ∼S ⊃ ∼D 4, Simplification 6. ~~D ⊃ ~~S 5, Transposition 7. D ⊃ S 6, Double negation 8. E ⊃ D 2, Simplification 9. (∼E ⊃ ∼C) ● (E ⊃ D ) 2, Commutation 10. ∼E ⊃ ∼C 9, Simplification 11. ~~C ⊃ ~~E 10, Transposition 13. C ⊃ E 11, Double negation 14. O ⊃ E 3,13, Hypothetical syllogism 15. O ⊃ D 14,8, Hypothetical syllogism 16. O ⊃ S 16,7, Hypothetical syllogism Edwin