Theorem nfsn

Description: Bound-variable hypothesis builder for singletons. (Contributed by NM, 14-Nov-1995)

	Ref	Expression
Hypothesis	nfsn.1	|- F/_ x A
Assertion	nfsn	|- F/_ x { A }

Proof

Step	Hyp	Ref	Expression
1		nfsn.1	|- F/_ x A
2		dfsn2	|- { A } = { A , A }
3	1 1	nfpr	|- F/_ x { A , A }
4	2 3	nfcxfr	|- F/_ x { A }