Theorem inf5

Description: The statement "there exists a set that is a proper subset of its union" is equivalent to the Axiom of Infinity (see Theorem infeq5 ). This provides us with a very compact way to express the Axiom of Infinity using only elementary symbols. (Contributed by NM, 3-Jun-2005)

	Ref	Expression
Assertion	inf5	|- E. x x C. U. x

Proof

Step	Hyp	Ref	Expression
1		omex	|- _om e. _V
2		infeq5i	|- ( _om e. _V -> E. x x C. U. x )
3	1 2	ax-mp	|- E. x x C. U. x