1. (P . Q) -> (R v S) :. (P -> R) v (Q -> S) --------------------------------- 2. ~(P . Q) v (R v S) 1 Material Implication 3. (~P v ~Q) v (R v S) 2 De Morgan's Law 4. ~P v (~Q v R) v S 3 Association 5. ~P v (R v ~Q) v S 4 Commutation 6. (~P v R) v (~Q v S) 5 Association 7. (P -> R) v (Q -> S) 6 Material Implication