Theorem nfvd

Description: nfv with antecedent. Useful in proofs of deduction versions of bound-variable hypothesis builders such as nfimd . (Contributed by Mario Carneiro, 6-Oct-2016)

	Ref	Expression
Assertion	nfvd	$$⊢\phi \to Ⅎx\psi$$

Proof

Step	Hyp	Ref	Expression
1		nfv	$$⊢Ⅎx\psi$$
2	1	a1i	$$⊢\phi \to Ⅎx\psi$$