Theorem eliminable1

Description: A theorem used to prove the base case of the Eliminability Theorem (see section comment). (Contributed by BJ, 19-Oct-2019) (Proof modification is discouraged.) (New usage is discouraged.)

	Ref	Expression
Assertion	eliminable1	|- ( y e. { x | ph } <-> [ y / x ] ph )

Proof

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