1. (P . Q) -> (R v S) :. (P -> R) v (Q -> S)
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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