Exercises 46–49 establish rules for null quantification that
we can use when a quantified variable does not appear in part
of a statement.
46. Establish these logical equivalences, where x does not
occur as a free variable in A. Assume that the domain is
a) (∀xP (x)) ∨ A ≡ ∀x(P (x) ∨ A)
b) (∃xP (x)) ∨ A ≡ ∃x(P (x) ∨ A)
my doubt is what is exactly “A” in in this logical expressions