Theorem nfnd

Description: Deduction associated with nfnt . (Contributed by Mario Carneiro, 24-Sep-2016)

	Ref	Expression
Hypothesis	nfnd.1	$$⊢\phi \to Ⅎx\psi$$
Assertion	nfnd	$$⊢\phi \to Ⅎx\neg \psi$$

Proof

Step	Hyp	Ref	Expression
1		nfnd.1	$$⊢\phi \to Ⅎx\psi$$
2		nfnt	$$⊢Ⅎx\psi \to Ⅎx\neg \psi$$
3	1 2	syl	$$⊢\phi \to Ⅎx\neg \psi$$