Theorem issettru

Description: Weak version of isset . (Contributed by BJ, 24-Apr-2024)

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

Proof

Step	Hyp	Ref	Expression
1		vextru	|- x e. { y | T. }
2	1	biantru	|- ( x = A <-> ( x = A /\ x e. { y | T. } ) )
3	2	exbii	|- ( E. x x = A <-> E. x ( x = A /\ x e. { y | T. } ) )
4		dfclel	|- ( A e. { y | T. } <-> E. x ( x = A /\ x e. { y | T. } ) )
5	3 4	bitr4i	|- ( E. x x = A <-> A e. { y | T. } )