Theorem cbviotav

Description: Change bound variables in a description binder. Usage of this theorem is discouraged because it depends on ax-13 . Use the weaker cbviotavw when possible. (Contributed by Andrew Salmon, 1-Aug-2011) (New usage is discouraged.)

	Ref	Expression
Hypothesis	cbviotav.1	$$⊢x=y\to \left(\phi \leftrightarrow \psi \right)$$
Assertion	cbviotav	$$⊢\left(\iota x|\phi \right)=\left(\iota y|\psi \right)$$

Proof

Step	Hyp	Ref	Expression
1		cbviotav.1	$$⊢x=y\to \left(\phi \leftrightarrow \psi \right)$$
2		nfv	$$⊢Ⅎy\phi$$
3		nfv	$$⊢Ⅎx\psi$$
4	1 2 3	cbviota	$$⊢\left(\iota x|\phi \right)=\left(\iota y|\psi \right)$$