Theorem bj-19.9htbi 34579

Description: Strengthening 19.9ht 2319 by replacing its succedent with a biconditional (19.9t 2202 does have a biconditional succedent). This propagates. (Contributed by BJ, 20-Oct-2019.)

Assertion

Ref	Expression
bj-19.9htbi	⊢ (∀𝑥(𝜑 → ∀𝑥𝜑) → (∃𝑥𝜑 ↔ 𝜑))

Proof of Theorem bj-19.9htbi

Step	Hyp	Ref	Expression
1		19.9ht 2319	. 2 ⊢ (∀𝑥(𝜑 → ∀𝑥𝜑) → (∃𝑥𝜑 → 𝜑))
2		19.8a 2178	. 2 ⊢ (𝜑 → ∃𝑥𝜑)
3	1, 2	impbid1 228	1 ⊢ (∀𝑥(𝜑 → ∀𝑥𝜑) → (∃𝑥𝜑 ↔ 𝜑))

Syntax hints:   → wi 4   ↔ wb 209  ∀wal 1541  ∃wex 1787

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1803  ax-4 1817  ax-5 1918  ax-6 1976  ax-7 2016  ax-10 2141  ax-12 2175

This theorem depends on definitions:  df-bi 210  df-ex 1788  df-nf 1792

This theorem is referenced by:  bj-hbntbi  34580