Theorem sbc2ieOLD

Description: Obsolete version of sbc2ie as of 12-Oct-2024. (Contributed by NM, 16-Dec-2008) (Revised by Mario Carneiro, 19-Dec-2013) (Proof modification is discouraged.) (New usage is discouraged.)

	Ref	Expression
Hypotheses	sbc2ieOLD.1	$$⊢A\in \mathrm{V}$$
	sbc2ieOLD.2	$$⊢B\in \mathrm{V}$$
	sbc2ieOLD.3	$$⊢\left(x=A\wedge y=B\right)\to \left(\phi \leftrightarrow \psi \right)$$
Assertion	sbc2ieOLD	$$⊢\underset{\dot{}}{[}A/x\underset{\dot{}}{]}\underset{\dot{}}{[}B/y\underset{\dot{}}{]}\phi \leftrightarrow \psi$$

Proof

Step	Hyp	Ref	Expression
1		sbc2ieOLD.1	$$⊢A\in \mathrm{V}$$
2		sbc2ieOLD.2	$$⊢B\in \mathrm{V}$$
3		sbc2ieOLD.3	$$⊢\left(x=A\wedge y=B\right)\to \left(\phi \leftrightarrow \psi \right)$$
4		nfv	$$⊢Ⅎx\psi$$
5		nfv	$$⊢Ⅎy\psi$$
6	2	nfth	$$⊢ℲxB\in \mathrm{V}$$
7	4 5 6 3	sbc2iegf	$$⊢\left(A\in \mathrm{V}\wedge B\in \mathrm{V}\right)\to \left(\underset{\dot{}}{[}A/x\underset{\dot{}}{]}\underset{\dot{}}{[}B/y\underset{\dot{}}{]}\phi \leftrightarrow \psi \right)$$
8	1 2 7	mp2an	$$⊢\underset{\dot{}}{[}A/x\underset{\dot{}}{]}\underset{\dot{}}{[}B/y\underset{\dot{}}{]}\phi \leftrightarrow \psi$$