Description: Axiom of Specialization.
A quantified wff implies the wff without a
quantifier (i.e. an instance, or special case, of the generalized wff).
In other words if something is true for all , it is true for any
specific (that would typically occur
as a free variable in the wff
substituted for ). (A free variable
is one that does not occur in
the scope of a quantifier: and are both free in ,
but only is free in .) Axiom scheme C5' in [Megill]
p. 448 (p. 16 of the preprint). Also appears as Axiom B5 of [Tarski]
p. 67 (under his system S2, defined in the last paragraph on p. 77).
Note that the converse of this axiom does not hold in general, but a
weaker inference form of the converse holds and is expressed as rule
ax-gen1618. Conditional forms of the converse are given
ax-c142222, ax-c162223, and ax-51704.
Unlike the more general textbook Axiom of Specialization, we cannot choose
a variable different from for the special case. For
requires the assistance of equality axioms, and we deal with it later
after we introduce the definition of proper substitution - see stdpc42094.