|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 2196 and was replaced with this
shorter ax-c11n 2197 ("n" for "new") in May
2008. The old axiom is proved
from this one as theorem axc11 2011. Conversely, this axiom is proved from
ax-c11 2196 as theorem axc11nfromc11 2234.
This axiom was proved redundant in July 2015. See theorem axc11n 2006.
This axiom is obsolete and should no longer be used. It is proved above
as theorem axc11n 2006. (Contributed by NM, 16-May-2008.)
(New usage is discouraged.)