1. M v (D · L) 2. B ⊃ ~(M v L) /~B 3. M v (L · D) 1, Commutation 4. M v L 4, Simplification 5. ~~(M v L) ⊃ ~B 2, Transposition 6. (M v L) ⊃ ~B 5, Double negation 7. ~B 6,4, Modus ponens Edwin