Using the definitions of the quantifiers, it is straightforward to argue that, if Q does not contain
the variable x and the universe is non-empty, then the following equivalences hold:
(1) ?xP(x) ? Q ? ?x(P(x) ? Q) (2) ?xP(x) ? Q ? ?x(P(x) ? Q)
Explain how these equivalences can be used to demonstrate the following:
(a) ?xP(x) ? ?xQ(x) ? ?x?y(P(x) ? Q(y))
(b) ?xP(x) ? ?xQ(x) ? ?x?y(P(x) ? Q(y))
(c) ?xP(x) ? ?xQ(x) ? ?x?y(P(x) ? Q(y))
Clearly, similar equivalences can be shown to hold when ? is replaced with ?