Theorem nfa2

Description: Lemma 24 of Monk2 p. 114. (Contributed by Mario Carneiro, 24-Sep-2016) Remove dependency on ax-12 . (Revised by Wolf Lammen, 18-Oct-2021)

	Ref	Expression
Assertion	nfa2	$$⊢Ⅎx\forall y\forall x\phi$$

Proof

Step	Hyp	Ref	Expression
1		alcom	$$⊢\forall y\forall x\phi \leftrightarrow \forall x\forall y\phi$$
2		nfa1	$$⊢Ⅎx\forall x\forall y\phi$$
3	1 2	nfxfr	$$⊢Ⅎx\forall y\forall x\phi$$