Theorem bj-cbvalvv 36875

Description: Universally quantifying over a non-occurring variable is independent of that variable, over ax-1 6-- ax-5 1912 and the existence axiom extru 1977. See bj-cbvaw 36877 for a strengthening. (Contributed by BJ, 8-Mar-2026.) (Proof modification is discouraged.)

Assertion

Ref	Expression
bj-cbvalvv	⊢ (∃𝑥𝜑 → (∀𝑥𝜓 → ∀𝑦𝜓))

Distinct variable groups:   𝜓,𝑥   𝜓,𝑦

Allowed substitution hints:   𝜑(𝑥,𝑦)

Proof of Theorem bj-cbvalvv

Step	Hyp	Ref	Expression
1		bj-spvw 36871	. . 3 ⊢ (∃𝑥𝜑 → (𝜓 ↔ ∀𝑥𝜓))
2	1	biimprd 248	. 2 ⊢ (∃𝑥𝜑 → (∀𝑥𝜓 → 𝜓))
3		ax-5 1912	. 2 ⊢ (𝜓 → ∀𝑦𝜓)
4	2, 3	syl6 35	1 ⊢ (∃𝑥𝜑 → (∀𝑥𝜓 → ∀𝑦𝜓))

Syntax hints:   → wi 4  ∀wal 1540  ∃wex 1781

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1797  ax-4 1811  ax-5 1912

This theorem depends on definitions:  df-bi 207  df-ex 1782

This theorem is referenced by:  bj-cbvaw  36877  bj-cbveaw  36879