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Theorem hbe1 2143
 Description: The setvar 𝑥 is not free in ∃𝑥𝜑. Corresponds to the axiom (5) of modal logic (see also modal5 2155). (Contributed by NM, 24-Jan-1993.)
Assertion
Ref Expression
hbe1 (∃𝑥𝜑 → ∀𝑥𝑥𝜑)

Proof of Theorem hbe1
StepHypRef Expression
1 df-ex 1777 . 2 (∃𝑥𝜑 ↔ ¬ ∀𝑥 ¬ 𝜑)
2 hbn1 2142 . 2 (¬ ∀𝑥 ¬ 𝜑 → ∀𝑥 ¬ ∀𝑥 ¬ 𝜑)
31, 2hbxfrbi 1821 1 (∃𝑥𝜑 → ∀𝑥𝑥𝜑)
 Colors of variables: wff setvar class Syntax hints:  ¬ wn 3   → wi 4  ∀wal 1531  ∃wex 1776 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1792  ax-4 1806  ax-10 2141 This theorem depends on definitions:  df-bi 209  df-ex 1777 This theorem is referenced by:  nfe1  2150  equs5eALT  2381  nfeqf2  2391  equs5e  2477  axie1  2785  bj-wnf2  34052  bj-nnfe1  34089  ac6s6  35449  exlimexi  40858  vk15.4j  40862  vk15.4jVD  41248
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