|Description: Axiom of Quantifier
Substitution. One of the equality and substitution
axioms of predicate calculus with equality. Appears as Lemma L12 in
[Megill] p. 445 (p. 12 of the preprint).
The original version of this axiom was ax-c11 2218 and was replaced with this
shorter ax-c11n 2219 ("n" for "new") in May
2008. The old axiom is proved
from this one as theorem axc11 2054. Conversely, this axiom is proved from
ax-c11 2218 as theorem axc11nfromc11 2256.
This axiom was proved redundant in July 2015. See theorem axc11n 2049.
This axiom is obsolete and should no longer be used. It is proved above
as theorem axc11n 2049. (Contributed by NM, 16-May-2008.)
(New usage is discouraged.)