Theorem eliminable-velab

Description: A theorem used to prove the base case of the Eliminability Theorem (see section comment): variable belongs to abstraction. (Contributed by BJ, 30-Apr-2024) (Proof modification is discouraged.) (New usage is discouraged.)

	Ref	Expression
Assertion	eliminable-velab	|- ( y e. { x | ph } <-> [ y / x ] ph )

Proof

Step	Hyp	Ref	Expression
1		df-clab	|- ( y e. { x | ph } <-> [ y / x ] ph )