Theorem cbvex2vv

Description: Rule used to change bound variables, using implicit substitution. Usage of this theorem is discouraged because it depends on ax-13 . Use the weaker cbvex2vw if possible. (Contributed by NM, 26-Jul-1995) Remove dependency on ax-10 . (Revised by Wolf Lammen, 18-Jul-2021) (New usage is discouraged.)

	Ref	Expression
Hypothesis	cbval2vv.1	⊢ ( ( 𝑥 = 𝑧 ∧ 𝑦 = 𝑤 ) → ( 𝜑 ↔ 𝜓 ) )
Assertion	cbvex2vv	⊢ ( ∃ 𝑥 ∃ 𝑦 𝜑 ↔ ∃ 𝑧 ∃ 𝑤 𝜓 )

Proof

Step	Hyp	Ref	Expression
1		cbval2vv.1	⊢ ( ( 𝑥 = 𝑧 ∧ 𝑦 = 𝑤 ) → ( 𝜑 ↔ 𝜓 ) )
2	1	cbvexdva	⊢ ( 𝑥 = 𝑧 → ( ∃ 𝑦 𝜑 ↔ ∃ 𝑤 𝜓 ) )
3	2	cbvexv	⊢ ( ∃ 𝑥 ∃ 𝑦 𝜑 ↔ ∃ 𝑧 ∃ 𝑤 𝜓 )