Theorem sbciegOLD

Description: Obsolete version of sbcieg as of 12-Oct-2024. (Contributed by NM, 10-Nov-2005) (Proof modification is discouraged.) (New usage is discouraged.)

	Ref	Expression
Hypothesis	sbciegOLD.1	$$⊢x=A\to \left(\phi \leftrightarrow \psi \right)$$
Assertion	sbciegOLD	$$⊢A\in V\to \left(\underset{\dot{}}{[}A/x\underset{\dot{}}{]}\phi \leftrightarrow \psi \right)$$

Proof

Step	Hyp	Ref	Expression
1		sbciegOLD.1	$$⊢x=A\to \left(\phi \leftrightarrow \psi \right)$$
2		nfv	$$⊢Ⅎx\psi$$
3	2 1	sbciegf	$$⊢A\in V\to \left(\underset{\dot{}}{[}A/x\underset{\dot{}}{]}\phi \leftrightarrow \psi \right)$$