Use an ordinary proof (not conditional or indirect proof): 1. G ⊃ (H ⊃ K) 2. (H ∨ ∼M) ⊃ ∼K 3. H / ∼G 4. H ∨ ∼M 3, addition 5. ~K 2,4 modus ponens 6. (G ∙ H) ⊃ K 1, importation 7. ~(G ∙ H) 6,5, modus tollens 8. ~G ∨ ~H 7, deMorgan's law 9. ~H ∨ ~G 8, commutation 10. ~~H ∨ ~G 3, double negation 11. ~G 9,10, disjunctive syllogism Edwin