1. (G • S) → D 2. (S → D) → P 3. G /P | 4. ~P Assumption for indirect proof | 5. ~(S → D) 2,4, Modus tollens | 6. ~(~S v D) 5, Material implication | 7. ~~S • ~D 6, deMorgan's law | 8. S • ~D 7, double negation | 9. ~D • S 8, commutation |10. ~D 9, simplification |11. ~(G • S) 1,10, Modus tollens |12. ~G v ~S 11, deMorgan's law |13. S • ~D 9, commutation |14. S 13, simplification |15. ~S v ~G 12, commutation |16. ~~S 14, double negation |17. ~G 15,16 disjunctive syllogism |18. G • ~G 2,17 conjunction 19. P Lines 4-18 for indirect proof Edwin