Theorem nfn

Description: Inference associated with nfnt . (Contributed by Mario Carneiro, 11-Aug-2016) df-nf changed. (Revised by Wolf Lammen, 18-Sep-2021)

	Ref	Expression
Hypothesis	nfn.1	$$⊢Ⅎx\phi$$
Assertion	nfn	$$⊢Ⅎx\neg \phi$$

Proof

Step	Hyp	Ref	Expression
1		nfn.1	$$⊢Ⅎx\phi$$
2		nfnt	$$⊢Ⅎx\phi \to Ⅎx\neg \phi$$
3	1 2	ax-mp	$$⊢Ⅎx\neg \phi$$