1. B ≡ (A • D) 2. ~A ⊃ (~B ⊃ C) / A ∨ C |3. ~(A ∨ C) Assumption for Indirect Proof |4. ~A • ~C 3, DeMorgan's Law |5. ~A 4, simplification |6. ~B ⊃ C 2,5, Modus Ponens |7. ~C ⊃ ~~B 6, transposition |8. ~C ⊃ B 7, double negation |9. ~C • ~A 4, transposition |10. ~C 9, simplification |11. B 8, Mudus Ponens |12. [B ⊃ (A • D)] • [(A • D) ⊃ B] 1, Material Equivalence |13. B ⊃ (A • D) 12, simplification |14. A • D 13,11 |15. A 14, simplification |16. A • ~A 15,5, conjunction 17. A ∨ C lines 3--16 Indirect Proof Edwin