Theorem nfaba1OLD

Description: Obsolete version of nfaba1 as of 14-May-2025. (Contributed by Mario Carneiro, 14-Oct-2016) (Revised by Gino Giotto, 20-Jan-2024) (Proof modification is discouraged.) (New usage is discouraged.)

	Ref	Expression
Assertion	nfaba1OLD	|- F/_ x { y | A. x ph }

Proof

Step	Hyp	Ref	Expression
1		nfa1	|- F/ x A. x ph
2	1	nfab	|- F/_ x { y | A. x ph }