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Theorem bj-hbntbi 34623
Description: Strengthening hbnt 2295 by replacing its succedent with a biconditional. See also hbntg 33500 and hbntal 41846. (Contributed by BJ, 20-Oct-2019.) Proved from bj-19.9htbi 34622. (Proof modification is discouraged.)
Assertion
Ref Expression
bj-hbntbi (∀𝑥(𝜑 → ∀𝑥𝜑) → (¬ 𝜑 ↔ ∀𝑥 ¬ 𝜑))

Proof of Theorem bj-hbntbi
StepHypRef Expression
1 bj-19.9htbi 34622 . . . 4 (∀𝑥(𝜑 → ∀𝑥𝜑) → (∃𝑥𝜑𝜑))
21bicomd 226 . . 3 (∀𝑥(𝜑 → ∀𝑥𝜑) → (𝜑 ↔ ∃𝑥𝜑))
32notbid 321 . 2 (∀𝑥(𝜑 → ∀𝑥𝜑) → (¬ 𝜑 ↔ ¬ ∃𝑥𝜑))
4 alnex 1789 . 2 (∀𝑥 ¬ 𝜑 ↔ ¬ ∃𝑥𝜑)
53, 4bitr4di 292 1 (∀𝑥(𝜑 → ∀𝑥𝜑) → (¬ 𝜑 ↔ ∀𝑥 ¬ 𝜑))
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  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: (None)
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