Theorem bj-issettru

Description: Weak version of isset without ax-ext . (Contributed by BJ, 24-Apr-2024) (Proof modification is discouraged.)

	Ref	Expression
Assertion	bj-issettru	|- ( E. x x = A <-> A e. { y | T. } )

Proof

Step	Hyp	Ref	Expression
1		bj-denotes	|- ( E. x x = A <-> E. z z = A )
2		bj-denoteslem	|- ( E. z z = A <-> A e. { y | T. } )
3	1 2	bitri	|- ( E. x x = A <-> A e. { y | T. } )