Theorem cbvex2v

Description: Rule used to change bound variables, using implicit substitution. Version of cbvex2 with a disjoint variable condition, which does not require ax-13 . (Contributed by NM, 14-Sep-2003) (Revised by BJ, 16-Jun-2019)

	Ref	Expression
Hypotheses	cbval2v.1	$$⊢Ⅎz\phi$$
	cbval2v.2	$$⊢Ⅎw\phi$$
	cbval2v.3	$$⊢Ⅎx\psi$$
	cbval2v.4	$$⊢Ⅎy\psi$$
	cbval2v.5	$$⊢\left(x=z\wedge y=w\right)\to \left(\phi \leftrightarrow \psi \right)$$
Assertion	cbvex2v	$$⊢\exists x\exists y\phi \leftrightarrow \exists z\exists w\psi$$

Proof

Step	Hyp	Ref	Expression
1		cbval2v.1	$$⊢Ⅎz\phi$$
2		cbval2v.2	$$⊢Ⅎw\phi$$
3		cbval2v.3	$$⊢Ⅎx\psi$$
4		cbval2v.4	$$⊢Ⅎy\psi$$
5		cbval2v.5	$$⊢\left(x=z\wedge y=w\right)\to \left(\phi \leftrightarrow \psi \right)$$
6	1	nfn	$$⊢Ⅎz\neg \phi$$
7	2	nfn	$$⊢Ⅎw\neg \phi$$
8	3	nfn	$$⊢Ⅎx\neg \psi$$
9	4	nfn	$$⊢Ⅎy\neg \psi$$
10	5	notbid	$$⊢\left(x=z\wedge y=w\right)\to \left(\neg \phi \leftrightarrow \neg \psi \right)$$
11	6 7 8 9 10	cbval2v	$$⊢\forall x\forall y\neg \phi \leftrightarrow \forall z\forall w\neg \psi$$
12	11	notbii	$$⊢\neg \forall x\forall y\neg \phi \leftrightarrow \neg \forall z\forall w\neg \psi$$
13		2exnaln	$$⊢\exists x\exists y\phi \leftrightarrow \neg \forall x\forall y\neg \phi$$
14		2exnaln	$$⊢\exists z\exists w\psi \leftrightarrow \neg \forall z\forall w\neg \psi$$
15	12 13 14	3bitr4i	$$⊢\exists x\exists y\phi \leftrightarrow \exists z\exists w\psi$$