1. (O ⊃ R) ⊃ S 2. (P ⊃ R) ⊃ ~S/ ~R 3. ~~S ⊃ ~(P ⊃ R) 2, transposition 4. S ⊃ ~(P ⊃ R) 3, double negation 5. (O ⊃ R) ⊃ ~(P ⊃ R) 1,4, hypothetical syllogism 6. (~O v R) ⊃ ~(P ⊃ R) 5, material implication 7. (~O v R) ⊃ ~(~P v R) 6, material implication 8. (~O v R) ⊃ (~~P • ~R) 7, deMorgan's law 9. (~O v R) ⊃ (P • ~R) 8, material implication 10. ~(~O v R) v (P • ~R) 9, material implication 11. (~~O • ~R) v (P • ~R) 10, deMorgan's law 12. (O • ~R) v (P • ~R) 11, double negation 13. (O v P) • ~R 12, distribution 14. ~R • (O v P) 13, commutation 15. ~R 14, simplification Edwin