Theorem cbvralsvwOLD

Description: Obsolete version of cbvralsvw as of 21-Aug-2025. (Contributed by NM, 20-Nov-2005) Avoid ax-13 . (Revised by GG, 10-Jan-2024) (Proof shortened by Wolf Lammen, 8-Mar-2025) (Proof modification is discouraged.) (New usage is discouraged.)

	Ref	Expression
Assertion	cbvralsvwOLD	$$⊢\forall x\in A\phi \leftrightarrow \forall y\in A\left[y/x\right]\phi$$

Proof

Step	Hyp	Ref	Expression
1		nfv	$$⊢Ⅎy\phi$$
2		nfs1v	$$⊢Ⅎx\left[y/x\right]\phi$$
3		sbequ12	$$⊢x=y\to \left(\phi \leftrightarrow \left[y/x\right]\phi \right)$$
4	1 2 3	cbvralw	$$⊢\forall x\in A\phi \leftrightarrow \forall y\in A\left[y/x\right]\phi$$