Exercise

1. Write a natural-deduction

₁

(p^q^r) → (PV¬qV¬r)

This is a more general version of de Morgan's law (4).

2. Write a natural-deduction proof of the most general de Morgan's law (4):

42 = (P₁ ^^ Pn) → (P₁ VV-pn)

where n > 2.

proof of the following WFF: