Theorem vtoclOLD

Description: Obsolete version of vtocl as of 20-Jun-2025. (Contributed by NM, 30-Aug-1993) Remove dependency on ax-10 . (Revised by BJ, 29-Nov-2020) (Proof shortened by SN, 20-Apr-2024) (Proof modification is discouraged.) (New usage is discouraged.)

	Ref	Expression
Hypotheses	vtocl.1	⊢ 𝐴 ∈ V
	vtocl.2	⊢ ( 𝑥 = 𝐴 → ( 𝜑 ↔ 𝜓 ) )
	vtocl.3	⊢ 𝜑
Assertion	vtoclOLD	⊢ 𝜓

Proof

Step	Hyp	Ref	Expression
1		vtocl.1	⊢ 𝐴 ∈ V
2		vtocl.2	⊢ ( 𝑥 = 𝐴 → ( 𝜑 ↔ 𝜓 ) )
3		vtocl.3	⊢ 𝜑
4	3 2	mpbii	⊢ ( 𝑥 = 𝐴 → 𝜓 )
5	1	isseti	⊢ ∃ 𝑥 𝑥 = 𝐴
6	4 5	exlimiiv	⊢ 𝜓