|Description: Axiom of Existence. One
of the equality and substitution axioms of
predicate calculus with equality. This axiom tells us is that at least
one thing exists. In this form (not requiring that 𝑥 and 𝑦 be
distinct) it was used in an axiom system of Tarski (see Axiom B7' in
footnote 1 of [KalishMontague] p.
81.) It is equivalent to axiom scheme
C10' in [Megill] p. 448 (p. 16 of the
preprint); the equivalence is
established by axc10 2143 and ax6fromc10 32701. A more convenient form of this
axiom is ax6e 2141, which has additional remarks.
Raph Levien proved the independence of this axiom from the other logical
axioms on 12-Apr-2005. See item 16 at
ax-6 1836 can be proved from the weaker version ax6v 1837
requiring that the
variables be distinct; see theorem ax6 2142.
ax-6 1836 can also be proved from the Axiom of
Separation (in the form that
we use that axiom, where free variables are not universally quantified).
See theorem ax6vsep 4562.
Except by ax6v 1837, this axiom should not be referenced
use theorem ax6 2142. (Contributed by NM, 10-Jan-1993.)
(New usage is discouraged.)