Theorem nfv

Description: If x is not present in ph , then x is not free in ph . (Contributed by Mario Carneiro, 11-Aug-2016) Definition change. (Revised by Wolf Lammen, 12-Sep-2021)

	Ref	Expression
Assertion	nfv	⊢ Ⅎ 𝑥 𝜑

Proof

Step	Hyp	Ref	Expression
1		ax5ea	⊢ ( ∃ 𝑥 𝜑 → ∀ 𝑥 𝜑 )
2	1	nfi	⊢ Ⅎ 𝑥 𝜑