Theorem nfsab1

Description: Bound-variable hypothesis builder for a class abstraction. (Contributed by Mario Carneiro, 11-Aug-2016) Remove use of ax-12 . (Revised by SN, 20-Sep-2023)

	Ref	Expression
Assertion	nfsab1	|- F/ x y e. { x | ph }

Proof

Step	Hyp	Ref	Expression
1		df-clab	|- ( y e. { x | ph } <-> [ y / x ] ph )
2		nfs1v	|- F/ x [ y / x ] ph
3	1 2	nfxfr	|- F/ x y e. { x | ph }